Monday, 8 September 2014

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

Wednesday, 3 September 2014

Clarence-Moreton Basin Geology Video

The NSW Office of Water have posted an excellent video summary of the geology of the Clarence-Moreton Basin. It provides an excellent overview.






Monday, 1 September 2014

Geological libraries

Sometimes it is important to get your geological references in the right order. Here is a cartoon by Chris Slane illustrating just how important it is to get an accurate geological library.




Monday, 25 August 2014

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.

Thursday, 21 August 2014

Facebook, night times and Iceland volcanoes

The Northern Rivers Geology blog has nearly a hundred thousand page views! I’m very excited about how much of a success this blog has been. I do want to continue to reach out to a large audience so I’ve taken a reluctant step into social media. I have set up a Facebook Page for the blog which contains links to the latest blog updates as well as other interesting geologically related matters. Let's see how it goes. If you are a Facebook user please follow me. Followers on Facebook can post their own interesting information or even ask questions. Of course readers can continue to comment as usual on this blog.

A picture of sandstone with rock hammer marks at night: doesn't really work.
On another matter, I was travelling into Queensland earlier this week via the Mount Lindesay Highway. It is a scenic but winding road (I was going to use the adjective ‘windy’ but since the weather that day was windy it could have got confusing - crazy English language). I noticed many interesting road cuttings including what appeared to be a coal seam. But, I could not stop because time was against me. I returned back the same way that night so I thought I’d try and do something I’ve never done night-time geology. It was not very successful. Trying to identify the larger scale features in a cutting by torch and car light is not an easy task. Even trying to look at sand grains was beyond me. My assessment of night time geology, don’t bother!

On yet another matter, I want to draw readers attention to this weeks volcanic activity in Iceland. Some interesting things are occurring under glacial cover. The only way that geologists can have an idea of what is going on is by measuring earthquakes. The number of earthquakes around two important concealed volcanoes has been in the many thousands this week. This has made processing the data time-consuming but presently the seismic records indicate some strange "goings on". In particular it appears that magma from the volcano Bardarbunga has made its way into fissures that are part of another volcano, Grimsvotn. This is quite unusual and with the added background these volcanoes have a very turbulent history and have taken many lives, all the more complicated. Volcano café has a good summary of the situation.

Friday, 8 August 2014

Crystals or No Crystals?

The landscapes of the mountains surrounding the Tweed Valley are very spectacular. I have discussed some of the facets of the Tweed Volcano and Mount Warning area in previous posts. However, I have not covered much on the main rock type that is mainly responsible for the rugged steep cliffs and valleys of the Nightcap National Park World Heritage Area. This rock is the Nimbin Rhyolite, a quartz rich lava that was dominant in the final phases of the Tweed Volcano. Because of its resistance to weathering it results in inspiring cliffs and rugged ranges.

Rhyolite is a volcanic rock that contains a high volume of silica (quartz) in it. Because of the silica content rhyolite lavas tend to be “sticky” and slow moving. This also causes gases to be trapped in the lava or magma chamber feeding the lava flows. The release of trapped gases can cause explosive eruptions. Therefore, accompanying the lava flows there are also deposits of volcanic ash and glass caused by the rapid cooling of lava during explosive eruptions. All of these features are present in the Nightcap Ranges and surrounding areas.

In a future post I will show a picture of a Nimbin Rhyolite lava which exhibits flow banding. There are many examples of flow banding in lava near Minyon Falls. It is a tricky lava to look at in hand specimen because it is very fine grained. You can only see occasional tiny specks that are crystals but most of the time it is just a grey mass. In outcrop you might see some flow structures like the one pictured, but generally it is a boring looking rock! The same rock is in the Mount Matheson area. Smith and Houston (1995) referred to this rhyolite as crystal-poor rhyolite. It compares very differently to the crystal-rich rhyolite identified elsewhere in the area.

As for the crystal rich rhyolite, I was lucky enough to go for a walk in a property that has just been purchased by the NSW National Parks and Wildlife Service. It is located in the valley between the Goonengerry and Nightcap National Parks. While inspecting the excellent work done to remove exotic weeds from this property and celebrate the inclusion of an important vegetative link between National Parks. I came across some good examples of the crystal-rich rhyolite. In these samples the rock contains large quartz crystals which are very evident (see the picture below). The more crystalline form of rhyolite occurs in about a third of the total area mapped as rhyolite. This includes the area from the Koonyum and Goonengerry ranges in the east to Whian Whian in the west.

Quartz crystals in Nimbin Rhyolite - upper Coopers Creek area
Smith and Houston (1995) observe the crystal abundance is related to the vent (or group of vents) from which the lava was erupted. Only occasionally do crystal rich and crystal poor varieties occur on top or under each other indicating a high degree of lava mixing. The relationship between specific vents and crystal richness shows the vents must have been tapping different magma sources (different magma chambers). Alternatively the vents may have erupted magma from a single, somewhat heterogeneous magma chamber.

However, it is worth noting there is a third major form of rhyolite in the area and is known as the volcanic glass, obsidian. This volcanic glass occurs around the bases of the major lava flows and is often referred to as perlite. The glass is rarely a massive unit but tends to appear brecciated and as an agglomerate. I will discuss this obsidian further in a future post as many interesting features and textures are preserved showing the way that rhyolite lavas move across the lands surface. In the mean time, it is worth remembering that lavas ain’t just lavas. There can be many differences which provide a window into how the landscape was formed.