Climate Change, Cloud-seeding, Floods, and Volcanic Mayhem

The Earth’s dynamics are complex and interrelated. For example, the chemical composition of magma below volcanoes in Indonesia has historically been linked to crop failures in Europe! This example from the eruption of Mount Tambora in 1815, where it is thought that temperatures caused the “the Year without a summer”. Meronen et al (2012) demonstrated that the gasses (such as sulphur dioxide) released from volcanic eruptions will have severe impacts on weather systems. These weather impacts include temperature but are also likely to cause other impacts either directly or indirectly, particularly precipitation resulting in major floods, particularly in Europe (Fagan 2000); though elsewhere there were flooding events that are apparently correlated. These floods often caused catastrophic damage.

Recently, of course, many many people have been affected in some way by, in some places, the worst floods recorded since, well, records have been documented in Australia. I've seen a few explanations of the "why" including the following three main ones:

• On social media I’ve seen the flooding attributed to the practice of “cloud seeding”, 

• I’ve also seen in the broader media the flooding attributed solely to anthropogenic climate change.

• The Bureau of Meterology lies the blame squarely on La Nina.

I’ll address all of the above and raise a hypothesis which is different, but in some way related to all of them.

Cloud seeding (introducing chemicals or particles into the atmosphere to encourage water droplets to form or increase in size) is sometimes recognised a as mechanism to increase the chance of rainfall. It is worth noting though, that statistically it is very difficult to prove that cloud seeding does much at all. The technique (if it can be called that), is applied mainly at dry times on the ground but when there is moderate atmospheric water content. Cloud seeding was tested in South East Queensland during the desperately bad drought from 2006 (Tessendorf et al 2012), though it was not possible to determine if clouds were formed due to the seeding material, or simply due to natural updrafts of air (one of the ways that clouds are formed naturally). I can find no record that cloud seeding took place in eastern Australia preceding the weather event, but it is worth noting that the volume/mass of seeding material needed would rule out seeding as causing the huge scale of rainfall.

The second reason I outlined above, is anthropogenic climate change. It is unfortunate that this has been attributed as a cause by many public figures and organisations, because it is impossible to attribute a single weather event to a climatic situation. Climate is a statistical representation of longer-term weather patterns and so one weather event does not demonstrate the climate, or a climate change. I will also note that if climate change was a factor in this weather event it is different from observed extreme weather events in Australia, where over the last several decades the incidence and frequency of storms and floods has decreased. Even models of storm frequency shows a decrease in frequency and a higher rate of break up of storms before impacting on the Australian landmass due to anthropogenic climate change (e.g. Abbs 2012). So, I have trouble pinning this flood event on anthropogenic climate change, or even natural climate change.

The third reason outlined seems to be the most likely of the three listed, and indeed I cannot argue with it much, except to potentially add a geological factor. Yes, you guessed it, volcanic eruptions. On the 15th of January this year, there was an extreme eruption of the Hunga Tonga –Hunga Ha'apai volcano. On facebook I re-posted a video, that demonstrated the scale of the eruption. The immediate particulates and aerosols (including sulphur dioxide) generated by the eruption past through the atmosphere across northern Queensland in the next several days. This material continued to circulate in various levels in the atmosphere over the subsequent weeks. So, a hypothesis is that if you combine the increased air moisture as a result of Coral Sea water temperature during this El Nina weather pattern we are in, combined with the blocking high pressure system in southern Australia (a common Australian summer climatic feature), with the natural effect of a huge volume of natural “cloud seeding” sourced from the volcanic eruption, this may have resulted in the extreme rainfall in eastern Australia. This would reflect the historical impacts on weather and floods resulting from volcanic events elsewhere in the world over recorded history, and reasonable enough that I think it worth considering.

Of course, speculation as to the “why” does not help those who have been so adversely affected (even killed) during the floods, but having some idea as to “why” can help us plan for future weather events. As a former Lismore resident, my thoughts go out to those in Lismore as well as those further up and down the coastal strip who are still living through the damage of the floods.

For some old posts on how volcanic eruptions from the Tonga area can affect the beaches of our coastline click here: 

Pacific Islands on Holiday to the North Coast

Tonga Comes to Visit Again

References/bibliography:

*Abbs, D. (2012). The impact of climate change on the climatology of tropical cyclones in the Australia region. CSIRO Climate Adaptation Flagship Working paper No.11.

*Fagan, B (2000) The little Ice Age: How Climate Made History, 1300-1850, Basic Books, New York.

*Meronen, H. et al (2012) Climate effects of northern hemisphere volcanic eruptions in an Earth System Model, Atmospheric Research, pp107-118.

*Tessendorf, S.A. et al (2012) The Queensland Cloud Seeding Research Program, American Meteorological Society, vol 93: issue 1.

Volcanic shockwave

A post a little off topic again today. This post is motivated by several related stories in the media. The first is a follow up from an earlier blog post where I criticised the Australian ABC for reporting an eruption in Iceland that was not even confirmed. A day or two later a large eruption occurred in our closest neighbour Papua New Guinea. The eruption was very large and was not even reported by the ABC – though it was picked up by ABC America! It occurred at Tavurvur Volcano near the mostly abandoned city of Rabaul.

On the 11th of September it will be the 100 year anniversary of Australia’s first military engagement in World War 1. Australian soldiers and sailors attacked German positions in the then German Colony of New Guinea. This first engagement, in which both Australian, German and ‘native’ soldiers were killed occurred near Rabaul. The occupation by Australian Soldiers led to Australian administration over Papua New Guinea until 1975. A short account of the battle can be read on the Australian War Memorial Website.

Finally, on the weekend a tourist recorded the moment when Tavurvur volcano erupted again. Though not as large an eruption as the initial one, the power of the volcano is clearly visible. The Youtube video shows massive lava bombs (probably bigger than cars) falling after the eruption and spectacularly a shockwave travelling through the air and hitting the camera. It is worth watching.

Too often we, in Australia forget that we have neighbours. Our news seems to be from the USA, UK a few European countries and ‘home’. But we always seem to forget our near neighbours, Papua New Guinea, Indonesia, East Timor and New Zealand. Let’s not forget the Solomon Islands and even France too (New Caledonia). I’ve previously posted on Indonesia and now I’ve mentioned in passing Papua New Guinea. These are important countries to know about and are so interesting in many ways, one of which is geology. It is beyond the scope of this blog to look in detail at these countries but we should as they affect us, even the geology of those places

ABC reporters cause a volcano to erupt

"Bararbunga Erupts" was the headline on the Australian Broadcasting Corporation (ABC) Television Bulletins on Saturday night. I've been following events in Iceland so I was interested when the ABC said that it had erupted. At first I was impressed the ABC was able to report an eruption on the other side of the world so quickly (much quicker than any sources I'd seen)... but sadly there was very little detail in the report that actually confirmed an eruption. Yesterday ABC online reported "Lava erupting from a massive volcano under an Icelandic glacier has prompted authorities to issue a red alert to the aviation industry amid fears of significant ash emissions." Sadly, science related reporting by the ABC has been on the decline for years. At the time of writing this post 24 hours after the above ABC news story there has been no definite evidence of an eruption.

VolcanoCafe summarises the current situation:

"...there are so far no other signs of volcanic activity. There is no gas measurements (if they are taken) indicating an eruption being close, neither are there gas or particles in the glacial run off indicating melting ice from an eruption."

VolcanoCafe goes on to say that one outcome may be: 

"the seismic activity decreases and the intrusion lose momentum and no eruption happens at this time. For every day this scenario becomes less likely."

How can the ABC report an eruption has occurred when there is little evidence to suggest it has? Is this a symptom of the ABC losing its ability to report on scientific matters and instead focusing on exciting or political headlines? Even the ABCs flagship science program Catalyst now dismisses research that is carried out by certain groups as evidence that the results are wrong. Catalyst seems to fail to explain why research is flawed in a scientific way. This is a big concern for me because I feel it is degrading science. So much so it is degrading science into politics. Scientific outcomes are questioned on the basis of who did it rather than how it was done.

Now we have the ABC not even knowing when a volcano erupts. It is now more important than ever to question popular science reports.

Update: Another day passes (four days since the ABC report). Still no confirmed evidence an eruption at Bardarbunga had occurred and the Iceland Met Office had reduced its flight path warning a day after the ABC news... Yet no more news on the ABC. Apparently the lack of bad news from Iceland is not news at all. Closer to home - According to the Smithsonian Institute a large explosive eruption occurred at Tarvurvur crater, Rabaul, Papua New Guinea,  on 28th August 2014. Ash emissions reached an altitude of 60,000 ft.

Update: The Iceland Met Office reported that a surveillance flight on the night of the 27th "discovered a row of 10-15 m deep cauldrons south of the Bárðarbunga caldera. They form a 6-4 km long line. The cauldrons have been formed as a result of melting, possibly a sub-glacial eruption, uncertain when."

Update: almost a week after the story of the "eruption" Bardarbunga finally erupts! Iceland Met Office aviation code still Orange. VolcanoCafe has the details.

References/bibliography:

*ABC Newsonline, Iceland volcanic Eruption Closes Airspace, http://www.abc.net.au/news/2014-08-24/iceland-volcanic-eruption-closes-air-space/5692296 accessed 2014-08-25

*VolcanoCafé, Bárðarbunga – Nature of the beast, http://volcanocafe.wordpress.com/2014/08/24/bardarbunga-nature-of-the-beast/ accessed 2014-08-25.

Are our volcanoes extinct?

Firstly, I've been a bit quiet on the blogging front for a couple of weeks. There has been a lot going on personally which has meant very little time for research or blog posts. I usually have a few scheduled posts up my sleeve for those times when I simply don't have the time... but as a measure of how busy I've been, even these have run out.

Having said all that, I must point out another interesting post by New England self-government advocate Jim Belshaw. It is interesting because it takes us back over a hundred years and shows us that we can sometimes have a little laugh about silly geological ideas from back then. But, it is important to know that miss-understandings of geology continue to this day, including a belief by some that Mount Warning (for example) might erupt again or that we are due for a magnitude 7.0 earthquake etc.

Pacific Islands on holiday to the North Coast

I often find some stories in newspapers touch too lightly on the subject of geology. These articles are often quite limited in scope and generally indicate quite simplistic notions of natural processes. This morning when reading a local newspaper The Tweed Daily News, I came across one such article. A link can to the article can be found here. This article is interesting because it covers some surprising points, but as Dr Malcom Clark an Environmental Geochemist from Southern Cross University implies in the article, there is more to the story than just a once-off beaching of pumice on Kingscliff Beach.

Pumice is a highly vesicular (aerated) volcanic glass. It is created when super-hot, highly pressurized rock is violently ejected from a volcano, especially those found in volcanic island arcs which are near active subduction zones. The unusual foamy feel of pumice occurs because of simultaneous rapid cooling and rapid depressurization. During the eruption the air bubbles are frozen in the rock. The amount of air trapped means that pumice usually has the unusual property of a rock being able to float on water.

If we work backward in time from the Tweed Daily News article a story starts to emerge on how the pumice on the beach got there. The first thing to note is that there are no active volcanoes on the Australian mainland or close to the eastern Australian coast. So, the pumice must have been brought in from somewhere else. Pumice has been common on Byron Bay beaches for the last few weeks ever since winter storms gave a good battering the coast in June. But a large amount of Pumice was also observed on the Queensland sunshine coast in April following late summer storms and the tail ends of cyclones. The storms force floating materials like rubbish and pumice onshore. This gives a clue about movement. It has taken a month or two to travel down the east coast on prevailing currents such as the south moving Eastern Australian Current. But there are no active volcanoes in Queenland either.

Bryan et al (2004) published an interesting article in Earth and Planetary Science Letters on pumice that was washed ashore all down the east coast of Australia in 2002. Here lies more of the answer. Bryan et al (2004) demonstrated that the pumice rafts were transported a vast distance across the Coral Sea and South Pacific Ocean, taking about almost a year to complete its trip on the prevailing currents and winds (the pumice was even blown backwards at one stage by a tropical cyclone). Surprisingly the 2002 Pumice landfall came from the Tonga area (North of an island and seamount chain that stretches to New Zealand called the Kermadec Islands), which is a long way away! Between the Kermadec Islands and Australia lies the Solomon Islands, Vanuatu and Fiji which all have active volcanic systems.  However, The pumice that washed ashore in 2002 was erupted in a submarine volcano (underwater) un-excitingly named Volcano 0403-091 from the Kermadec Islands and swept past all the other islands.

As for the current pumice landfall, in the last year there has been several eruptions of island arc volcanoes the Vanuatu islands, but significantly in July 2012 there was a major eruption of pumice from the vicinity of the Havre Seamount in the Karmadec Islands (Smithsonian Institute 2012). The time between eruption and East Australian landfall is interesting because it is similar to that for the 2001-2002 event discussed by Bryan et al (2004). More recently in 2012 an article was published (Bryan et al 2012) that demonstrated that rapid and long distance movement can be a frequent occurrence. So, maybe the pumice on our beach today this is just a little bit of history repeating – a bit of a pacific volcano on a holiday to the north coast of New South Wales.

Postscript:

Scott Bryan sent me this email yesterday. Being so informative I thought I should post it here.

Hi Rodney,

...I was actually at point lookout (nth Stradbroke) today collecting the pumice. The pumice is indeed from the Havre submarine eruption in the Kermadecs last year. There is a good summary of the eruption and discovery of the pumice rafts at the global volcanism program of the smithsonian institution (USA) at www.volcano.si.edu. 

This pumice is distinctive in being white when fresh; there is also a lot of grey/dark grey pumice at north stradbroke which is from tonga and the previous eruptions I have published on. It has been eroded out of the beach dunes.

The main influx along our shores began in mid-late march, continuing up to early May. There has been a bit of a break, but with the windy and wild weather this last weekend, some more pumice has come in, as well as probably reworked material (abraded and cleaned of attached biota) which seems to be what has washed up at Kingscliff. Newly washed up pumice will be covered in a black or dark green slime (Cyanobacteria) and be loaded with lots and large goose barnacles. You will also find on closer inspection, some molluscs, bristle worms (feeding on the barnacles), bryozoans, hydroids, anemones. Look up Denis Riek and his web page www.roboastra.com - he has taken some fantastic close ups of the pumice and biota found on it at Brunswick Heads.

This pumice has travelled about 3000 km in 8-12 months. We have observed it as far north as Heron Island.

Let me know if you need more info.

I would appreciate further reports of any new strandings as I have a Masters student beginning her research on this pumice and the attached biota. New strandings give us a temporal perspective as the biota mature and diversify with time and also begin recruiting species locally.

References/bibliography:

*Bryan, Scott Edward, S., Cook, Alex, Evans, Jason, Hebden, Kerry, Hurrey, Lucy, Colls, Peter, Jell, John S., Weatherley, Dion, & Firn, Jennifer (2012) Rapid, long-distance dispersal by pumice rafting. PLoS ONE, V7.
*Byran, S.E., Cook, A., Evans, J.P., Colls, P.W., Wells, M.G., Lawrence, M.G., Jell, J.S., Greig, A. & Leslie, R. 2004. Pumice Rafting and faunal dispersion during 2001-2002 in the Southwest Pacific: record of a dacitic submarine explosive eruption from Tonga. Earth and Planetary Science Letters V227.
*Smithsonian Institute 2012. Havre Seamount. Bulletin of the Global Volcanism Network. Smithsonian Institute. September 2012.

Ahh Ahh

Readers of this blog will probably notice I have an intense interest in volcanology. Volcanology has a wide variety of aspects some of which I’m comfortable, some less so. These aspects can be the chemistry of molten materials, the physics of earthquakes or the dynamic processes of pyroclastic flows. Volcanology and igneous rocks more generally seem to have their own weird language that can stop you and make you turn to a dictionary.

One of my favourite words in the ‘language’ of geology is the name of a large scale structure of lava flows. It is called aa. So, turning to a dictionary (this time the Omnificent English Dictionary in Limerick Form) you get the following possible definitions:

No consonants! Does this seem ominous? 
It's with rough-surfaced lava synonymous.
Yet the thought it conveys
With two capital A's 
Is, of course, Alcoholics Anonymous. 
By Chris J. Strolin


I'm ascending a gentle volcano; 
The climb's not the cause of my strain. 
No, This lava is stressed, 
Pretty jagged at best. 
Cut my feet on sharp aa — the pain, Oh! 
By Aliza


On Hawaii the lava's aflame 
As observers, in awe, cry its name. 
When that molten rock's oozing 
Down paths of its choosing, 
It's "A'a!" that tourists exclaim. 
By David

Probably one of the more interesting dictionary definitions I’ve seen. I Hope that helps with understanding? If these are a little bit obscure you can always visit my Glossary.

A Volcanic Sedimentary Rock

My Wife and I have been in South Brisbane for a few weeks while my daughter has received treatment in a hospital there so I have not compiled any posts on the geology of the Northern Rivers during this time. However, I thought it might be worthwhile to tell you about an interesting rock I found in Brisbane that is of a type that can occasionally be found in the Northern Rivers especially in the New England Tablelands.

One morning while walking to the hospital, down the driveway of the apartment I was staying at I caught a glimpse of a rock fragment that was different to what I had previously seen in this area. The driveway was cut into weathered old Paleozoic aged rock called the Bunya Phyllite. But the rock fragment that I saw of interest because it was quite different from the phyllite as it had a large quartz cobble in it. Later when walking back to the apartment I had a closer glimpse. It appeared that this rock had fallen down the slope and there were other rocks inconsistent with the phyllite. I picked the piece up that first got my attention and washed it clean. It was a conglomerate, with large rounded clasts of quartzite and basalt and an angular clast of the aforementioned phyllite. The clasts were cemented together with a grey material with small angular crystal fragments. All of this was a surprise until I remembered that I was close to Kangaroo Point which is a cliff line made from a volcanic rock called the Brisbane Tuff part of a Triassic aged volcanic terrain.

It was apparent that what I had was conglomerate formed in the throws of the volcanic eruptions that created the Brisbane Tuff. The Roach (1997) and earlier authors interpreted the Brisbane Tuff as series of pyroclastic flows, surges and air falls that were deposited in pre-existing valleys formed during the Triassic. The valleys probably have had rocky streams evident from the rounded nature of the clasts in the conglomerate. After or during an eruption of the volcano combined with a lots of rain or the failure of a natural dam or lake a mud flow probably ran down the valley mixing all the rock, debris, mud and what ever got in its way stopping after the energy had been spent. The conglomerate would then have been covered and preserved by material from subsequent eruptions.

The sort of volcanic related mud flow described above is called a lahar. They are actually quite common in modern volcanic terrains but are often quickly eroded away so tend to be a little less common than would be expected in older volcanic terrains. Lahars are part of a larger group of volcanic-sedimentary rocks called volcaniclastic rocks. Volcaniclastic rocks are found in the Northern Rivers areas, particularly in the areas of the escarpment and tablelands where the Permian (pre-Brisbane Tuff) Wandsworth Vocanic Group is present (Barnes et at 1991), (The Wandsworth Volcanic Group includes such diverse units as the Annalee Pyroclasics near Armidale to the Drake Volcanics near Drake). The group is very extensive and deserves to be considered in several future posts. It is also worth noting that the Brisbane Tuff was deposited at the same time in a similar way as the Chillingham Volcanics which filled the bottom of the Ipswich Basin and now outcrops in the Tweed and lower Richmond River Valleys.

References/bibliography:

*Barnes, R., Brown, R.E., Brownlow, J.W. & Stroud, W.J. 1991. Late Permian Volcanics in the New England - The Wandsworth Volcanic Group. Quarterly Notes of the New South Wales Geological Survey.
NSW geosurvey quarterly notes, 84.
*Roach, A. 1997. Late Triassic Volcanism of the Ipswich Basin. Macquarie University, PhD Thesis.

Into the Parrots Nest

At least 3 lava flows are evident from the different 'steps'

I had the opportunity a few weeks back to visit a quarry near the locality called Canaiba situated mid way between Casino and Lismore. The quarry is an operating variable quality rock quarry probably excavating Miocene aged basalt lavas from the geological unit known as the Lismore Basalt or possibly the earlier Eocene aged Alstonville Basalt. It was a site I'd wanted to visit for quite a while because the quarry is located at the lower side of a long ridge with an old abandoned quarry located at the top of the ridge on the way to a locality called Parrots Nest. In my mind having two quarries could give an interesting perspective on the any variations in lava flows.  But even before I visited the old quarry, while I was driving along the road to visit the operating one I noticed an interesting feature in the shape of a spur from the main ridge. Visible were several 'steps' in the spur. These steps create what is referred to, unsurprisingly, a stepped topography.

The steps are caused by the erosion of different lava flows. The flows are up to 20 metres of so thick which according to Duggan and Mason (1978) is a bit uncharacteristic for the Lismore Basalt (thin 2-3 thick flows). Looking back along the ridge it is pretty evident that the flows are of consistent thickness through the whole area.  They are probably from the Lismore Basalt that are related to the formation of the Tweed Volcano which was centered around present day Mount Warning. I wonder if there were closer vents that could be the source of the lavas but there is little evidence of any in the immediate vicinity. Indeed authors such as Cotter (1998) feel that the pre-existing topography was such that the area through Blakebrook Quarry (another site north of the quarry I was visiting) through to places like Parrots Nest may have been a valley. The swift flowing basaltic lavas flowed down these valleys filling them and creating thick sequences of rock.

The red layer overlain by another basalt lava flow
indicates the presence of a fossil soil horizon

The operating quarry cuts several of the lava flows that make up the ridge, the boundaries of the lava flows were very easy to make out because of the weathered zones especially the presence of palaeosols, that is, fossil soil horizons. The palaeosol gives an idea of the nature of the eruptions of lava too. Obviously enough time needs to have passed for the formation of a soil profile to occur on the earlier lava flow before the next lava flows over the top of it. Depending on the climatic conditions this could be many decades between flows or even thousands of years.

Anyway, a good trip even if it was just for the palaeosol or the stepped topography alone. But I'd like to do another blog on some of the macro scale igneous textures that are present in the lava including dykes, vesicles, voids and veins and I've still not got to the top abandoned quarry but when time allows I'll get there. I took some samples at the operating quarry to examine under the microscope to see if there were any microscopic textures that are of interest too, but once again, time does not seem to be on my side... though I will get to these tasks sometime!

References/bibliography:

*Cotter, S. 1998. A Geochemical, Palaeomagnetic and Geomorphological Investigation of the Tertiary Volcanic Sequence of North Eastern New South Wales. Masters Thesis, Southern Cross University.
*Duggan, P.B., Mason, D.R. 1978. Stratigraphy of the Lamington Volcanics in Far Northeastern New South Wales. Australian Journal of Earth Sciences V25.

Drake mining: managing a muddy mess

Sorry it has taken some time for me to post. I have had very little time of late because of some health problems my daughter has been having. But she is better than ever so time to get some time back into geology matters again.

Drake has a history of gold mining spanning back to 1886 when gold was dredged from Plumbago Creek. Since then the source of much of the alluvial gold was found just to the north of Drake. Many pits were created in the search for gold since the 1920s. These pits were relatively large mines in themselves and were given names such as White Rock, Carrington, Strauss, Lady Hampden and others. The mines were a source of wealth (during the good times) and a source of debt (during the bad times) with the mining operations completely ceasing in the 1990’s.


One of the old pits at Drake shortly after treatment with red mud

The formation of gold in the gold fields just north of Drake are a little difficult to put together as there seems to be more than one period of mineral formation in the rock. The parent rock is lavas and pyroclastic deposits including tuff which is of andesite to rhyolite in chemical composition. These rocks are called the Drake Volcanics which are part of the spatially significant Wandsworth Volcanic Suite. It appears that a caldera once developed in the area and fluids heated by magma transported gold and other metals and concentrated them. This is called an epithermal mineral deposit. However, Houston (1999) demonstrated that overprinting much of this epithermal stage is another chemically different period of mineralisation possibly related to different intrusive introducing mineralised fluids. And finally much of the area has been affected by supergene enrichment, which is enrichment caused by natural transport of minerals in groundwater and the percolation of rainwater.

Because financial stresses encourage people to take shortcuts to save money several things have happened at Drake that has caused elevated metal contamination to the environment of Plumbago Creek, a tributary of the Clarence River. Though sometimes people are just lazy or even ignorant of the possible impacts of incorrectly disposing of waste materials (Just like at home). Mineral deposits of the type at Drake contains minerals called sulphides, these include pyrite (iron sulphide), chalcopyrite (copper-iron sulphide) and sphalerite (zinc-iron sulphide). When exposed to air and water these minerals break down creating acids (called acid mine drainage) that cause the metals to be dissolved in any waters and therefore easily discharged into the environment. This is what has happened at the old pits near Drake and also at the waste dumps and even the access roads which were surfaced with waste rock.

But the story of the Drake mines also involve another waste material deliberately brought in from central Queensland. This material is referred to as Red Mud and is caustic (highly alkaline) waste material from aluminium refineries. But this is actually a good news story! Basic chemistry demonstrates that when you add acid and alkaline material together the material becomes neutral and metal contaminants precipitate out meaning any discharged water is decontaminated. Essentially an environmentally serious problem (disposal of aluminium refinery waste) has actually proven to be a resource. The trials and remediation of the pits was so successful that the technique was patented and a commercial product developed out of the Red Mud and given the name TerraB.

Application of the Red Mud was both as slurry pumped by ‘sprinkler’ directly into contaminated water left at the site or incorporated into waste rock or used as treatment liners. The picture shows one of the pits that I visited more than a decade ago when this technique was being trialled. It may look bad but really it is just suspended sediment that will settle out, while the acid and heavy metals have been neutralised. Some trials in waste rock have even found that Red Mud can actually reduce the uptake of heavy metals by plants, better than traditional rehabilitation techniques such as lime (Maddocks et al 2009).

The area around drake is interesting for many a geological reason, from its formation, the minerals found, the historical mining, contamination and rehabilitation. Who would have thought that adding two waste products together would fix both problems?! Two wrongs do make a right!

References/bibliography:

*Clark, M.W., Walsh, S.R. & Smith, J.V. 2001. The distribution of heavy metals in an abandoned mining area; a case study of Strauss Pit, the Drake mining area, Australia: implications for the environmental management of mine sites. Environmental Geology v40.

*Houston, M.J. 1999. The Geology and Mineralisation of the Drake Mine Area, Northern New South Wales. Papers, New England Orogen Conference, Armidale 1999.

*Maddocks, G., Lin, C. & McConchie, D. 2009. Field scale remediate of mine wastes at an abandoned gold mine, Australia II: Effects on plant growth and groundwater. Environmental Geology

Who has heard of the Belmore Volcano?

Most of us know about the two large remnants of volcanic provinces in the region, one the Tweed Volcano and the other the Ebor Volcano. Many too will know that the Tweed Volcano erupted first (23 million years old) and as the Earths crust moved over the mantle the probable hot-spot that caused this volcano migrated further south and formed the Ebor Volcano (19 million years old). Few people will have heard of the Belmore Volcano, this is a volcanic area that is located roughly midway between the Tweed and Ebor volcanic provinces and it also erupted in the interval between the other two (21 million years).

Before I go on I should point out that the term volcano is used very loosely here as it may also consist of many active cones and vents which erupted at a similar time period and are related to each other. Indeed the definition of what a volcano is defined as (such as the terms central volcano and volcanic province) has been an on-going argument for a long period of time anyway!



Trachyte makes up Dome Mountain in the Fineflower area

The area of the Belmore Volcano is away from the main travelled routes and for that reason it has probably been relatively unnoticed for a period of time. It lies to the east of the village of Baryulgil in the southern areas of the Belmore State Forest and Mount Neville Nature Reserve which is about halfway to Coaldale as you head towards Grafton. It is near the southern extents of the Richmond Range. The volcanics have produced some very interesting and rugged landforms such as Dobie Mountain, Mount Mookima, Mount Neville and Dome Mountain.

Most of the lavas have been eroded away but many eruptive sources for the volcano have been identified including plugs, pipes, dykes and possibly some sills. The lavas and intrusion preserved were erupted through the rocks of the Mesozoic aged Clarence-Moreton Basin which outcrop in the area as the Kangaroo Creek Sandstone and Walloon Coal Measures (probably including the MacLean Sandstone Member), but get older as you head west towards the edge of the Basin. The Mesozoic rocks in the area is actually quite deformed (as far as the Clarence-Moreton Basin goes) with large north-south trending folds and several faults nearby. The folds are visible as ridges and valleys (except those landforms associated with the more recent Belmore volcanics).

The Belmore Volcano is interesting because it shows the migration path of the hot-spot that formed the volcanoes that occur along the northern rivers area. There are actually four recognised volcanoes/volcanic provinces. These are all evenly spaced both in distance and time of eruption. From north to south these are the Tweed (23Ma), Belmore (21Ma), Ebor (19Ma) and Comboyne (16Ma) with the migratory trail of the hot-spot lost after this point. Sutherland et al. (2005) demonstrates that the Belmore Volcano is also curious because of the lava type erupted, whereas the other volcanoes erupted mainly more mafic volcanics (basalts and andesites) with later minor more felsic phase (rhyolite, dacite and trachyte ), the Belmore had very little basalt but lots of trachyte. But Isotope analysis by Sutherland et al (2005) has shown that the Belmore Volcanics were associated with the same mantle plume that generated the other volcanoes listed above.

Like most other recognised volcanoes in the region there is an earlier basalt type rock which occurs in the area which appears to have little to do with the most recent volcanic rocks. This is no exception in the Belmore area, where a basalt (dated at 31Ma) is present just to the north of the main eruptive area. Very little is known about this earlier volcanism and how it ties in with the geological history of the region.

References/Bibliography:

*Sutherland, F.L., Graham, I.T., Zwingmann, H., Pogson, R.E. & Barron, B.J. 2005. Belmore Volcanic Province, northeastern New South Wales, and some implications for plume variations along Cenozoic migratory trails. Australian Journal of Earth Sciences V52.

The 'older' Rhyolite in the North East

In some of my earlier posts I mentioned that there are many areas in the mountains around the Tweed Valley that are comprised of rhyolite. I mentioned that this rhyolite was formed during eruptions associated with the Tweed Volcano during the Cenozoic era. This rhyolite is called the Nimbin Rhyolite or the Binna Burra Rhyolite (depending what side of the state border you are on). However, there is actually another large distribution of rhyolite not associated with the Tweed Volcano, erupting much earlier, during part of the Mesozoic known as the Triassic. These older mainly rhyolitic rocks are called the Chillingham Volcanics with the type location unsurprisingly located at Chillingham, a village west of Murwillimbah. Those of you who have seen my earlier posts will recognise that I have briefly mentioned the Chillingham Volcanics before, but in this post I intend to go into it further.

Layers of pyroclastics and volcaniclastic of the Chillingham Volcanics
(Murwillimbah - Kyogle Road)

The Chillingham Volcanics have been studied in a fair amount of detail by Roach (1997) in his thesis. This included all of the Triassic volcanic rocks from Brisbane to Uki. So, obviously there is a relationship with the rocks of the southern Queensland, Indeed Roach (1997) indicates that the Brisbane Tuff is a deposit of volcanic rock of rhyolitic composition. The Brisbane Tuff is most well known by the Kangaroo Point Cliffs opposite the Brisbane River in Brisbane City and was erupted during the same general period of time as the Chillingham Volcanics.

The Brisbane Tuff provides a miniature version of the Chillingham Volcanics and is well known because the volcanic centre can be identified in the northern suburbs of Brisbane and the tuff was laid down in the valleys that existed in the Palaeozoic aged basement. The situation which lead to the formation of the Brisbane Tuff also developed further west and south where a larger valley now known as the Ipswich Basin was forming. The eruptions occurred in and around the basin as the crust in this area was subsiding during thermal fluctuations and as the basin filled up with volcanic rocks subsidence continued leading to a very thick unit of mostly rhyolite and reworked volcanic rocks (actually a sedimentary rock known as a volcaniclastic rock). So the Chillingham Volcanics are actually the lower most stratigraphic unit in the Ipswich Basin.

The Chillingham volcanics are mainly comprised of rhyolite in the form of lavas, pyroclastic, ash and tuff deposits as well as the above mentioned volcaniclastics. Many volcanic vents are recognised from structural characteristics of the rocks, however, only one area really shows an obvious modern geomorphological character. This area is around Uki and Clarie Hall Dam where eruptions formed a large mass due to the slow moving nature of the lava. Interestingly the northern most parts of the Chillingham Volcanics in Queensland shows us that there was not just rhyolite but also some andesite and even basalt, but in the area between Chillingham and Uki it is pretty much all rhyolite.

Outcrops of the Chillingham volcanics occur over a long distance with the eastern most side of the Ipswich Basin exposed in New South Wales meaning that a band of the Chillingham Volcanics is visible within the eroded valleys of the Tweed Volcano. The band is actually interupted by the Mount Warning Complex which appears to have intruded right along the line of the pre-existing Chillingham Volcanics. Also the volcanics are covered by the Lamington Volcanics of the Tweed Volcano too, both along the Queensland Border and between Clarie Hall Dam and Evans Head. Indeed the Chillingham Volcanics appears to change composition through this area with authors such as Smith et al 1997 and Cotter 1998 identifying andestite and basalt at Evans Head and an area near Wardell.

The Chillingham Volcanics overlie palaeozoic aged rocks of the Beenleigh Block, mainly rocks of the Neranleigh-Fernvale Group. The overlying rocks are more components of the Ipswich Basin such as the Ipswich Coal Measures and its equivalent (such as the Evans Head Coal Measures).

Although I have said that the Chillingham Volcanics contain the older rhyolitic rock in this area, there are actually still older rhyolites in the region... But I'll talk about those rocks in a future post.

References/Bibliography:

*Cotter, S. 1998. A Geochemical, Palaeomagnetic and Geomorphological Investigation of the Tertiary Volcanic Sequence of North Eastern New South Wales. Masters Thesis, Southern Cross University.
*Roach, A. 1998. Late Triassic Volcanism of the Ipswich Basin, Masters Thesis, Macquarie University.
*Smith, J.V., Miyake, J., Houston, E.C. 1998. Mesozoic age for volcanic rocks at Evans Head, Northeastern New South Wales. Australian Journal of Earth Sciences V45

Mythical geology at the mouth of the Tweed River

My knowledge of Gaelic mythology is a bit limited but it is interesting to see where geology, Gaelic mythology, Captain Cook and Tweed heads have something in common. I’ve not been to Ireland or Scotland but I’ve experienced a feature that is quite famous in these countries that is also present on the northern rivers.

Fingal Head, clearly showing the basalt columns

Just to the south of the Tweed River mouth lies Fingal Head and Cook Island. Cook Island, is of course named after then-Lieutenant Cook who sailed along the section of coast in 1770. Fingal Head, however, is named after Fingal, a mythological Gaelic hero from Scotland, who never came to this part of Australia! So why is it named so?
To understand the name of Fingal Head you need to know about the story of the Giants Causeway in Ireland and Fingal’s Cave in Scotland. I’m not a good story teller so here is a link (if this link is still not working try this one instead). My summing up of the story is that one of the two warring giants built a causeway to the other side of the Irish Sea so that he could fight the other. The other giant tore it down so that only each side of the causeway remains, one in Northern Ireland the other, Western Scotland. Local tourist information says that Fingal Head is named after the Irish hero. This is actually incorrect, the Irish hero is named Finn MacCool. The name Tweed River should hint that it is actually the Scottish hero that Fingal Head is named after. So, where does the geology come in?

The giants causeway is made from basalt. The volume and thickness of the basalt lava flows means that different parts of the lava flow usually cool at different rates (though, as pointed out by Goehring et al. 2006, the actual mechanism is completely unknown). However, the general idea is that in the case of Fingal Head the lava flow has cooled quite quickly, resulting in contraction of the rock and cooling joints being formed. The incredible thing about nature is that these cooling joints forms columns of rock that are of similar thickness and cross sectional shape, usually hexagons. This formation style is called columnar basalt. Indeed the rock that makes up the causeway has been shown to extend under the sea all the way from Ireland to Scotland. While the scale is not as great as in the British Isles, Cook Island just a short distance off the coast is part of the same lava flow at Fingal Head. This area, therefore has very similar features as the Giants Causeway and in my opinion the name Fingal Head is very appropriate.

The lava at Fingal Head is apparently derived from the Tweed Volcano (classified as Lismore or Beechmont Basalt, depending on what side you are of the Queensland border). Whether it is a lava flow erupted from the original central vent or vents on the northern flank of the volcano is not known. It is worth knowing that columnar volcanic rock is actually fairly common. Indeed, even better columnar formations can be seen elsewhere in the region. If you travel inland from Bellingen up to Ebor and visit the waterfall there (Ebor Falls) you will be able to see some spectacular formations. Columnar jointing is not restricted to basalt lavas either, some rhyolite cliffs around the Tweed Volcano also show this feature too.

References/Bibliography:

*Goehring, L, Morris, S.W. &  Lin, Z. 2006. Experimental investigation of the scaling of columnar joints. Physical Review. V64.
*Stevens, N.C., Knutson, J., Ewart, A. & Duggan, M.B. 1989. Tweed. In Johnson, R.W. (ed). Intraplate Volcanism in Eastern Australia and New Zealand. Cambridge University Press.

Rocks and Landscapes of the Gold Coast Hinterland

Since rocks tend not to follow political boundaries but our understanding of them often does it is good to know about what is north of the Northern Rivers/New England Border in southern Queensland. Last year I was going to do a post on the Focal Peak Volcano but then I remembered that the Queensland Division of the Geological Society had produced some excellent publications on the subject and recommended one in particular, so the post was essentially a recommendation for the Book the Rocks and Landscapes of the National Parks of Southern Queensland. But I deliberately omitted from the post comments on another brilliant book that had recently been fully revised so that I could deal with is separately.

The other book is called Rocks and Landscapes of the Gold Coast Hinterland by Warwick Willmott. I enjoy this book very much because it is simple to understand but goes into a good amount of detail. It also shows you exactly where to go to see a feature of interest just like a self guided tour.

However, the detailed knowledge of the northern part of the Tweed Volcano may have skewed research and our understanding of the volcano in general. For instance, although the Tweed Volcano has been assumed to be centred around the site of present day Mount Warning in New South Wales most of our understanding including the detailed research of PhD and MSc level on the volcano actually comes from the University of Queensland. The University of Queensland has been the driving institution for decades in research on these northern flanks by exceptional researchers like Professor Anthony Ewart and Dr Jan Knutson.

As I have discussed in numerous other posts on the Tweed Volcano, the model of what the volcano looked like and how it was formed has recently been questioned by authors such as Cotter (1998). In my mind this raises some questions about elaborating the northern side of the volcano to the remainder in New South Wales. While I have nothing to question the good work on the northern side of the border, including the wonderful books produced by the Australian Geological Society's Queensland Division, it appears that the model of volcanism of the Tweed Volcano has been interpreted to fit into a Queensland model. This has occurred ever since authors like Duggan & Mason (1978) and continued to Stevens et al (1989) and most recently by Howden (2009). I do not question to model of rock formation to the north of the border (it works for what is there) but according to Cotter (1998) south of the border pre-volcanic geological conditions seemed to be different and this had a significant effect on the mode of volcanism in the area. This however, does not mean that the Rocks and Landscapes of the Gold Coast Hinterland is incorrect in any way on its description of Queensland geology, it is just important to note that interpreting the geology south of the border can sometimes be problematic even if a cursory look means that it appears reasonable.

But I have digressed a great deal. Back to the Book! The Rocks and Landscapes of the Gold Coast Hinterland is formatted in a way that makes it a geological tour. If you end up traveling through the Gold Coast area, do get a copy of this book. It is only about $12 including postage and is quite large and detailed for its price. In fact I'm surprised that the cost is so low, but I think that all the time that Warwick Willmott has put into writing it has been for free. As I have said in other posts, Warwick is one of the great science educators in Australia, and the book really helps understand the Gold Coast area a lot.

References/Bibliography:

*Cotter, S. 1998. A Geochemical, Palaeomagnetic and Geomorphological Investigation of the Tertiary Volcanic Sequence of North Eastern New South Wales. Masters Thesis, Southern Cross University.
*Duggan, P.B., Mason, D.R. 1978. Stratigraphy of the Lamington Volcanics in Far Northeastern New South Wales. Australian Journal of Earth Sciences V25.
*Howden, S. 2009. An Evaluation of Mafic Extrusives Spatially Assoicated with the South-Western Aspect of the Tweed Shield Volcano, BSc(Hons.) thesis, University of New England, Armidale.
*Stevens, N.C., Knutson, J., Ewart, A. & Duggan, M.B. 1989. Tweed. In Johnson, R.W. (ed). Intraplate Volcanism in Eastern Australia and New Zealand. Cambridge University Press.

A warning about Mount Warning

Here are some common quotes about Mount Warning:

"World Heritage listed Mount Warning (Wollumbin) is the remnant central plug of an ancient volcano." 

"The Mount Warning volcano was a huge shield volcano."

"Considered the central magma plug, Mt Warning and a system of ring dykes, being extremely hard rock, have resisted erosion, and dominate the valley landscape."

"Mt Warning, Wollumbin, the cloud catcher, is the basalt plug of the world's largest and oldest extinct volcano. "

"Now, Mt. Warning is the first place that that the sun hits at sunrise… the highest point in New South Wales….almost the highest in Australia!"

These are quotes typical of tourist and even educational resources. They are quite definite and the comments makes sense, mostly. There are also some points of view that I espoused for a long time... Except aspects of each of the quotes are technically wrong and in some cases completely wrong. Like my post on the "erosion caldera" something that is technically incorrect has become general knowledge. It is a little pedantic of me, but it is one of my hobby horses... so what is technically wrong with the quotes above?

Western face of Mount Warning (composed of syenite).
One of the ring dykes is visible in the foreground
and Mount Uki and the Pacific Ocean in the background

Interestingly, Stevens et al (1989) and earlier authors noted that the rock composition of the intrusions that make up Mount Warning (the Mount Warning Complex) is different from most of the lavas (The Lamington Volcanics) that exist in the region. It is also slightly older than most of the lavas. Geologically speaking the age difference is not huge at only about 2-3 million years, but still significant enough.

It is apparent from Smith & Houston (1995) and other authors that much of the rhyolite lavas that remain of the Lamington Volcanics were not erupted from the central area now the site of Mount Warning but from vents on the flanks. Given the coverage of the mafic components (the Lismore Basalt, for example) it is more difficult to identify any vents.  

An idea has been raised by Cotter (1998) which questions the volume of lava that was erupted from the Tweed Volcano. It is known that the Palaeozoic aged meta-sedimentary rocks of the Beenleigh Block, called the Neranleigh Fernvale Beds and the Mesozoic aged Chillingham Volcanics and Clarence Moreton Basin were not domed upwards by the underlying magma except a little around the Mount Warning Complex itself. However, other areas such as the nearby slightly older Focal Peak Volcano have been lifted by the Cenozoic aged volcanism. But in the case of Mount Warning, Cotter (1998) felt that lithology, the remnants of the rhyolitic lavas, the pre-existing Chillingham and Alstonville Volcanics was the main control on the geomorphology, not as suggested by others the volcanism that formed the shield volcano itself.

The idea suggested by Cotter (1998) has significant implications for the size of the Tweed Volcano. The volcano is considered the biggest by far of its age in eastern Australia. It appears likely that the extent of the shield volcano is not as great as originally thought. The underlying Chillingham Volcanics would have been an existing mountain range and therefore reduced the thickness of the Tweed volcanic pile and the Alstonville Basalts would have reduced the southerly extent. I think that when you add to this the idea that the rhyolite units have erupted away from Mount Warning, but instead from flanks on the volcano, the volume of lavas from the Tweed Volcano may actually be more in keeping with the other intra-plate volcanoes in Eastern Australia. It was also possible that before it was eroded into the present shape (which implies a central shield type volcano) it may have looked more irregular than we imagined...

But don't get me started on the comments about the biggest volcano in the world and the highest point in New South Wales!!! What were these people thinking?!

...but does any one want to talk down something that was presumed to be huge, just to something large? Emotionally, many (including myself) have an emotional attachment to the beauty and wonder of the Tweed Volcano, sometimes it is hard to take a step back and consider it is not quite as fabulous as originally thought, but what we see is still stunning... and it is still very, very big. To put that in perspective I think that even the small volcanoes in the region are stunning. We don't need to exaggerate something for it to inspire us.

Bibliography/References:

*Cotter, S. 1998. A Geochemical, Palaeomagnetic and Geomorphological Investigation of the Tertiary Volcanic Sequence of North Eastern New South Wales. Masters Thesis, Southern Cross University. 
*Smith, J.V. , Houston, E.C. 1995. Structure of lava flows of the Nimbin Rhyolite, northeast New South Wales. Australian Journal of Earth Sciences V42(1) p69-74.
*Stevens, N.C., Knutson, J., Ewart, A. & Duggan, M.B. 1989. Tweed. In Johnson, R.W. (ed). Intraplate Volcanism in Eastern Australia and New Zealand. Cambridge University Press.

A special volcano on the edge of the Northern Rivers

I have previously mentioned several volcanoes that have existed during the Cenozoic period in and around the Northern Rivers region of the New England. But, it is worth noting that there was once a period of significant volcanism earlier in the Cenozoic which defines the landscape of the Great Dividing Range south of Glen Innes, near the villages of Glencoe (with its excellent pub: The Red Lion Inn) and Ben Lomond. This area is the headwaters of many wild rivers found flowing down the rugged New England escarpment that are tributaries of the Clarence River. On the other side of the divide eventually join the Darling and then Murray River. The Maybole volcano was apparently centred at the modern day and generally unheard of locality, Maybole. It erupted lavas over a large area in every direction including large areas to the west, east and south east.

Maybole lies just on or just outside of the headwaters of the Northern Rivers but none-the-less is worth mentioning because of the extent of volcanic rock that appears to have originated from it. The rocks that have come from the Maybole Volcano are mostly basalt type rocks which were once referred to as the Eastern division of the Central Volcanic Province (Coenraads & Ollier 1992), now referred to as the Maybole Volcanics but still part of the Central Volcanic Province according to Vickery et al (2007). The Maybole Volcanics are comprised of alkali olivine basalt to slightly less silica undersaturated basalt and andesite and reworked volcanic material (epiclastic and volcaniclastic sedimentary rocks) and was erupted around 36-39 million years ago.

Coenraads & Ollier (1992) identified that Maybole was a significant volcano by determining the thickness of basalt that occurred in the region and noticing that at Maybole the thickness was significant at several hundred metres. There are also apparently some dykes and vents that are present. Additionally, they had a close look at drainage patterns and realised that they radiated like the spokes on a bicycle, a classical indication of volcanic geomorphology.

Since Coenraads & Ollier (1992), Vickery et al (2007) has undertaken a major review of the Central Volcanic Province and delineated several constituents of the province. The most significant along this part of the Great Divide is now known as the Maybole Volcanics, obviously directly associated with the Maybole volcano. The age of the Central Volcanic Province including the Maybole Volcanics shows that these rocks are too old to be associated with the Eastern Australian hotspot which formed many of the other major volcanic centres in the region (such as the Focal Peak, Tweed and Ebor Volcanoes). Some time after the end of volcanism from the Maybole Volcano  other volcanoes between about 14-24Ma erupted their lavas over the top of the Maybole Volcanic suite rocks.

Interestingly, it appears that the Maybole Volcanics had affected exactly where the Great Divide was situated because the nature of the existing range was such that the lavas filled the valleys creating thick volcanic piles while the existing hills were only covered with thin layers. This meant redirection of streams and when the rock was eroded the more erodible hills were turned into valleys and the valleys became hills caped with basalt. This is termed an inverted topography. But more about this in another post.

Interestingly, Coenraads & Ollier (1992) have observed that the the great divide has moved over time with some of the old basalt filled valleys showing that they used to flow to the west but with the streams now flowing to the east. It actually appears that the Northern Rivers region is getting bigger!

Red Lion Inn (from Flickr)

PS. Like lots of geologists I like pubs with a good atmosphere and The Red Lion Inn at Glencoe is just such a beautiful place. It is an exceptional location to stop for a meal, especially during the middle of winter while snow is coming down. Alternatively, during autumn while the trees turn bright yellow and red, or during spring while the new leaves are coming out, or even summer! i.e. I recommend it!

References/bibliography:

*Coenraads, R. R., Ollier, C.D. 1992. Tectonics and Landforms of the New England Region in 1992 Field Conference - New England District. Geological Society of Australia Queensland Division.
*Vickery, N. M., Dawson, M.W., Sivell, W.J., Malloch, K.R., Dunlap, W.J. 2007. Cainozoic igneous rocks in the Bingara to Inverell area, northeastern New South Wales. Geological Survey of New South Wales Quarterly Notes v123.

The hiding peak at Glenugie forest

Some time ago Mark left a comment where he asked whether the basalt at Glenugie Peak (once known as Mount Elaine) was part of the Ebor Volcano. I didn't think it was likely but at that stage I did not know much about this peak, in fact I'd only glimpsed it through the trees while driving along the Pacific Highway to Grafton. Since then I've been trying to find out more about the peak, although I still have not had the chance to actually get there, staff from the New South Wales Geological Survey recently have reviewed the mapping of the area including the peak. What they observed reinforces my understanding that it is not related to the Ebor Volcano but the visit found out some very unusual things.

Glenugie Peak is hidden quite well by the forest all around as well as the lack of other hills to see it from. This means that it often goes unnoticed but if you have a look at a topographic map you will see that it is a very significant feature in the landscape. Before I learned what the rocks were here I thought it was likely to be an old flow of basalt from a period of volcanism that occurred before the chain of volcanoes from the East Australian Hot Spot. This is because there are many outliers of basalt that occur in the region that are too early for the hot spot volcanism. In addition, the old geological mapping of the area has Glenugie Peak being comprised of Tertiary aged extrusive Basalt. This contrasts with the surrounding rock which is the Grafton Formation of the Clarence Moreton basin.

I  came across Jopin (1968) who described a sample of the Glenugie Peak obtained from another authors petrographic analysis as Limbugite. I have heard of Limburgite before but I could not remember exactly what it was or the implications of such a rock type. I don't think I have ever even seen such a rock before. So, I had to look it up! Limburgite is essentially looks a like a basalt in hand specimen but contains no quartz and is so silica poor that not even feldspar is present in the rock.  Instead of feldspar (the most common rock forming mineral) other minerals called feldspathoids are present. This is termed silica under-saturation or ultramafic.

The NSW Geological Survey have now identified that the Glenugie Peak is intrusive and is a dyke, volcanic plug or similar. It has been intruded through the underlying sedimentary rocks of the Clarence Moreton Basin. Additionally, a review of mapping of the region that is being undertaken includes investigation of the rock composition at Glenugie Peak. The Investigation includes analysis of samples which identified two types of rock: Teschenite and Meltiegite. Teschenite and Meltiegite is quite consistent with the Limburgite classification by Joplin 1968. These two are also silica under-saturated rocks. The feldspathoid mineral in this rock is called nepheline.

So what, what does that mean? Well, these rocks are actually very unusual in the coastal region. Phonolite, a related but still not as silica-undersaturated (it is also higher in the elements sodium and potassium) as the rock found at Glenugie, occurs in the New England tablelands but this seems to be quite old in comparison to Glenugie Peak. These silica under-saturated rocks form where there is a significant thickness of continental crust allowing the bottom of the crust to partially melt (but not melt too much). The melted component then migrates and is emplaced either in more shallow crust or erupted to the surface. It is comparatively rare and unfortunately these rocks tend to weather easily making accurate chemical dating hard.

It seems that Glenugie Peak is made from a weird rock. I was very surprised (and excited) to see the unusual classifications that have been made. As far as I am aware this rock does not occur anywhere else nearby and even on an Australian scale is rare. When a fresh piece of rock is obtained the general appearance resembles basalt and therefore may be quickly passed over and forgotten. Luckily, the peak continues to be looked at and although nothing has been published yet it is exciting that more is being learnt about the geology of the region. Without the Geological Survey and university geology departments knowledge of our land would be so much less.

Knowing what I now do, the next time I'm spending some time in the Grafton area I'm going on a bushwalk to Glenugie Peak! Apparently it is within a flora reserve and is particularly good for bird spotting too.

Note: since writing the above post I have come across another early reference to Limbugite and Teschenite by Vallance et al (1969) who also refer to a 1919 description but unfortunately little extra information is given.

2nd note: since wrinting the above note I came accross a record from 1915 which includes analysis of apparently of one of the two types of rocks found at Mount Elaine. The geo-chemical classification of this rock (according to the TAS method) is a picro-basalt (essentiall a very low silica and very low sodium and potassium basalt).

References/bibliography:

Joplin, G. A., 1968, A Petrography of Australian Igneous Rocks, Angus and Robertson.
Valance, T.G., Wilkinson, J.F.G., Abbott, M.J., Faulks, I.G., Stewart, J.R., Bean, J.M., 1969, IX Mesozoic and Cainozoic Igneous Rocks, Journal of the Geological Society of Australia.V16.

Nimbin Rocks!?

Sadly, I don't visit Nimbin even though I live quite close. This is mainly because you do risk your health through passive (hemp) smoking, getting beaten up if you stumble across someones 'crop' while trying to find geological features in the bush, or just threatened with a knife for money so they can get their family birthday presents (or something important like that). Another thing too is the distrust that many people have in the area for geologists thinking in their ignorance of what I am trying to find may lead to a gas well in their front yard and assuming that I have to be working for a coal seam gas company.



One of the Nimbin Rocks, Cathederal Rock

 But one feature stands out near Nimbin and that is the Nimbin Rocks which tower above the surrounding valleys. 'Google' "Nimbin Rocks" and you will find lots of short snippets on these grand rock formations. Unfortunately, I've found that these descriptions are technically wrong. For instance wikipedia (and many, many travel websites) use terms to describe the Rocks as being derived from a dyke and also as being extrusive. Well, technically, a dyke is an intrusive body only and extrusive rocks are better known as lavas. So what is correct?

The Nimbin Rocks are comprised mainly of the quartz rich volcanic rock called rhyolite overlying a section of agglomerates (reworked volcanic rock) and volcanic glass known as perlite. Below the perlite lies basalts of the Kyogle Basalt. And here may lie the clue. The rocks appear to be layered because they are deposited on top of each other. First the Kyogle Basalt, then the perlite and agglomerates and then the rhyolite lavas (with some bands of perlite within it). The rhyolitic lavas are referred to as the Georgica Rhyolite Member according to Duggan and Mason (1974), or historically and more recently as Nimbin Rhyolite according to McElroy (1962) and Cotter (1998) and others.

If the Nimbin Rocks were related to a dyke they would have formed through pushing through the surrounding rocks such as those of the Kyogle Basalt or the Clarence Moreton Basin sediments, metamorphosing them and displaying different diagnostic textures than those I know about. However, it is still quite possible that the rocks may have been vents since the nearest identified vents seem to be about 8km away to the north east in the Nightcap Ranges and rhyolite lava flows tend to not move great distances, indeed rarely greater than 5km. However, the vents located further into the Nightcap Ranges are characterised by thick erosion resistant units of rhyolite which we don't see so much near Nimbin other than the Nimbin Rocks themselves. But conversely, the shape of the rock monoliths does imply a dyke.

So, what is the answer? Well the Nimbin Rocks are either one or more volcanic vents or they are the remnants of thick lava flows possibly from vents in the nightcap ranges located on the flanks of the Tweed Volcano. Which is almost not an answer at all. But one thing is obvious, it is interesting just how little we know about the landscape in which we live, work and see.

Blog Note: I like to provide photos for these sort of posts but recently where I store photos (skydrive and/or GoogleDocs) has changed its method for providing URLs to allow embedding of these files and Blogger doesn't like the new URLs. So, these next blogs might be a bit more bland looking until I figure out a better way to store and embed photos.

Since writing the above I have come across a report by Relph (1958) which says the following:

“Quartz-feldspar porphyry [granite, the intrusive equivalent of rhyolite] has intruded the sediments at Lillian Rock and the eastern portion of the Nimbin Rocks area. In the latter occurrence the porphyry forms two prominent pinnacles, with columnar jointing evident, and outcrops to the east, and in the bed of Goolmangar Creek. In neither case have the surrounding sediments been affected to any marked degree, but it is thought that it is intrusive and of dyke or plug form rather than of extrusive nature. Under the microscope this rock revealed no sign of flow structure.”

Although Relph considered two of the Nimbin Rocks intrusive he did not find any diagnostic evidence of them being either intrusive or extrusive.

References/Bibliography

*Cotter, S. 1998. A Geochemical, Palaeomagnetic and Geomorphological Investigation of the Tertiary Volcanic Sequence of North Eastern New South Wales. Masters Thesis, Southern Cross University.
*Duggan, P.B., Mason, D.R. 1978. Stratigraphy of the Lamington Volcanics in Far Northeastern New South Wales. Australian Journal of Earth Sciences V25.
*McElroy, C.T. 1969. The Clarence-Moreton Basin in New South Wales. In Packham, G.H.(ed) - The geology of New South Wales. Geological Society of Australia. Journal V16
*Relph, R.E. 1958: Geology of the Nimbin area. Technical Report. Department of Mines NSW, 3.
*Smith, J.V. , Houston, E.C. 1995. Structure of lava flows of the Nimbin Rhyolite, northeast New South Wales. Australian Journal of Earth Sciences V42(1) p69-74.

Looking out from the lookout at Point Lookout

The view of the National Park from Point Lookout

One of my favourite places is Point Lookout at the New England National Park between Ebor and Dorrigo. Point Lookout is spectacular for it scenery and feel. On most days you can see the pacific ocean while looking over rugged hills and valleys and I particularly like going there during winter where icicles hang from trees and the waterfalls below the peak are frozen. Point Lookout is nearly 1560metres high which I understand makes it the highest point in northern New South Wales. Like the beauty of the Mount Warning area and Tweed and Brunswick River region, Point lookout owes its attractiveness to the erosion of a large shield volcano.

Point lookout is located on the rim of an escarpment which formed through the erosion of the Cenozoic aged (in this case 19-18 million years) Ebor Volcano and the much older Devonian to Carboniferous (up to ~416Ma) accretionary complex rocks that make up the balance of the New England tablelands. Today, only the north western portions of the lavas (called the Ebor Volcanics) and the central weathered volcanic plug from the Ebor Volcano remain. Research by Ollier (1982) suggested that the central volcanic plug of Ebor Volcano was centred on what is called the crescent which is actually a fairly insignificant looking feature when compared with the rugged valleys today.

It is interesting to note that even though the nearby 23 Million year old Mount Warning (located near and over the Queensland border) is regarded as one of the biggest shield volcanoes in the southern hemisphere, having a height of around 2000 metres before it was eroded, the Ebor volcano was probably a similar size or bigger at its greatest too. It is a bit of a mystery why so little is left of Ebor Volcano when so much remains of the Tweed Volcano/Mount Warning.

The Crescent complex once thought to be Permian (290Ma-250Ma) as recently at the 1970's and was considered part of the intrusives that constitute the New England Batholith. In fact most of the most 'current' geological maps of the area were drawn at this time and so they are incorrect. But since investigations on the radial drainage patterns and geological features by Ollier in the late 1980s followed by dating by Gleadow and Ollier (1987) (which is difficult due to how weathered the Crescent is) and more recent work by Ashley et al (1995) now it is known to be the centre of the Ebor Volcano and aged around 19 Million Years. Ashley et al (1995) also discovered that a nearby basalt called the Doughboy Basalt was around 46 Million years old which is clearly not related to the Ebor volcano but is consistent with other locations where an older Cenozoic basalt is present before the hot spot volcanism that formed the Ebor, Mount Warning and other volcanoes existed.

When I was last at Point Lookout there were several bush walks from long and difficult to short and easy. The most difficult ones take you into the valleys where the rock has been eroded into the older accretionary complex. But even on the short one you can see some interesting 'recent' volcanic rocks. On a section of the walk around the top of the cliffs where security fences are necessary (lest you plummet away!) there is cuttings through the rock. In this rock look closely and you'll see some big crystals within a fine groundmass. This rock is a type of basalt called tholeiite (which means that it has crystalised with a certain geochemical signature) and the crystals are feldspars which is a common rock forming mineral. The feldspars here quite obvious and seem to catch the light at two angles, this feature is called twinning and is characteristic of the calcium rich variety of feldspar called plagioclase. Along the bigger walks below the point dacite can be found as well as basaltic and dacitic breccias at the stunningly beautiful during winter, weeping rock and numerous palaeosols.

The remnant of the shield volcano shows the characteristic radial drainage pattern for volcanic shields but the eroded central areas of the volcano (including the caldera if there was one) drains fairly directly to the east via the Nambucca River. The radially draining creeks and rivers are well known for their waterfalls such as Dangar Falls and Ebor Falls.

The road from Dorrigo to Armidale is not a busy route, it is often missed by many people but I always recommend people visit the New England tablelands because of its beauty and uniqueness in Australia. Point lookout is just off the Waterfall Way which name probably gives you an indication of many of the other attractions. In my opinion, the depths of winter are the best times to visit to get the mood and subtle beauty of the area. I should get back there myself... it has been too long since I was last there.

You may be interested in a self-guided geological tour. Bob and Nancy from Armidale have a wonderful site which includes an excellent (and expanding) range of geological tours including ones of the Northern Rivers Area. Their tour guide on Point Lookout can be accessed from their webpage (very much worth the look) or  directly linked from here.   

References/bibliography:

*Ashley, P.M., Duncan, R.A. & Freebrey, C.A. 1995 Ebor Volcano and the Crescent Complex, northeastern New South Wales: age and geological development. Australian Journal of Earth Sciences V42.
*Gleadow, A.J.W. & Ollier C.D. 1987 The age of gabbro at the Crescent, New South Wales. Australian Journal of Earth Sciences V34.
*Ollier, C.D. 1982 Geomorphology and tectonics of the Dorrigo Plateau, NSW. Australian Journal of Earth Sciences V29.

What is the Mount Warning erosion caldera?

It is very popular to refer to the Mount Warning area as the Mount Warning erosion caldera or Tweed Shield erosion caldera. Many sources indicate that it is the biggest erosion caldera in the world. For example Bigvolcano or good ol' wikipedia use the term. There are some very informative books by top class geologists such as Rocks and Landscapes of South East Queensland by Warwick Willmott also use the term. It is certainly an imposing volcanic influences landscape, but what is an erosion caldera anyway.

Ok. Let us start somewhere definite. A geological dictionary definition. Lets just look at caldera: A large circular crater left after the collapse or explosion of a volcanic cone. Now, lets look at erosion: The wearing away of rocks or other materials by the action of water or ice or wind.

So, Adding the term erosion to the front of the word caldera implies this: a landscape formed through the actions of wind or water or ice but also simultaneously formed through the collapse or explosion of a volcanic cone. Hopefully, you agree that this is possibly misleading. We have two different formation concepts equally applicable at the same time. What gives? How can the same feature form at the same site twice? once by erosion and once from the collapse of a magma chamber.

Mount Warning in the centre of the volcano remnant

Mount Warning was once the centre of a large volcanic cone called the Tweed Volcano. The centre of the Tweed Volcanic cone was a crater which may have collapsed or exploded as some stage to create a larger caldera. But this process is not definitely known because if this caldera actually existed it has since been eroded away to reveal the valley systems that we see today.

I think is is becoming obvious that there has been some sort of mistake in the development of the name erosion caldera. So, why use this term? A short answer is that most geologists tend not use this term, unless informally to illustrate the grand nature of some valleys that are formed in the remnants of large volcanos. That is not to say that some geologists don't mistakenly use the term anyway, I mean even geologists are human!

My suggestion, is not to use the term erosion caldera at all since it often results in confusion on the mechanism for the formation of thing it is actually used to describe.

The volcano of the Border Ranges - Focal Peak

I was going to do a blog on the Focal Peak Volcano and the Cenozoic aged volcanic rocks associated with it in the Northern Rivers/New England NSW but to get an understanding of these rocks on the southern side of the dotted line you really have to know a bit, or a lot about the geology across the border. With that in mind I was going to write this blog but then I remembered that the wonderful Queensland branch of the Geological Society of Australia have some excellent information sheets on Mount Barney and Mount Barlow that would do just the trick. So instead of starting from scratch I thought I'd just link directly to the PDF. Here it is.

The authors of this information sheet are Neville Stevens and Warwick Willmott who in my view are/were some of the best science educators in the country and happen to be geologists! I have enjoyed some of their presentations (and many others) at the Theodore Club in Brisbane when I lived there and it is one of the things I do miss about living away from that city. Alas, Neville passed away earlier this year.

While I'm talking about Queensland I should recommend a couple of books which gives an excellent account of the geology of Southern Queensland these are Rocks and Landscapes of the National Parks of Southern Queensland by Warwick Willmott and Rocks and Lanscapes of the Gold Coast Hinterland by the same author. I understand this Gold Coast one has just been revised and expanded. You can get a copy of the Southern Queensland one for less than $25 and the Gold Coast one for less than $15 including postage from the Queensland Division of the Geological Society of Australia. For details on ordering these books click here.