Every week I go through hundreds of images of volcanoes, and almost to a fault they are bombastic images of majestic strato volcanoes in dramatic light, or images of smoke and lava pouring out of equally majestic volcanoes, only problem is that I am bone tired of them since they are really bad if I want to make a certain point about volcanoes.
There have been two articles that I have wanted to write for more than a year, but have not been able to do since I could not find any photographic material at all to show what I wanted. A few days ago Vitton Georges posted a couple of pictures on his Facebook page that where so fabulous that I almost started to play lip-banjo out of sheer joy. So here are finally the two articles in one picture rich article.
But, by all means, let us start at the beginning.
All the images in this post are from the large volcano of Gorely. The volcano is a truly massive shield volcano that has gone through several phases. The bottom of the volcano is more than 25 kilometers across and it contains a massive circular caldera that is more than 12 kilometers across.
The shield volcano is in turn covered by no less than five strato volcanoes and numerous tuff cones; this makes it into a highly complex volcano. And herein lies the explanation to the oddity of the Gorely shield volcano, it is one of the few shield volcanoes on the planet that has suffered a super-eruption creating a huge ignimbrite area from its more than 100 cubic kilometer caldera forming VEI-7 eruption.
Last time Gorely had an eruption was 21st of August 2013.
In a volcano you have two typical reasons for earthquakes. Most of us jump when we see an earthquake in a volcano and quietly hope that it is due to magma infusion into the magmatic system of the volcano. But more often the earthquakes are caused by magma cooling, and as magma cools down it shrinks in size. This not only causes deflation of the volcano, it also causes something that is called blocking, and that is when the roof over the magma “chamber” slowly collapses. I have noticed that it is hard to encompass this function of a volcano since we can’t see the effects of the process in images, but thanks to Vitton Georges we can now do that in these spectacular images of cooled down magma in a lavatube.
Sometimes as the eruption stops magma is trapped in the tubes and stay in situ as it cools down. As that happen the magma will after a while have shrunk sufficiently to separate from the tube walls and as is shrinks it forms these beautiful “baguettes” of solidified magma.
Another process that happens to the poor trapped magma that has been trapped in the tube is that it is at shallow enough depth to degas. This causes further shrinkage, the amount is a factor of the amount of gas contained in the magma.
In the case of our magmatic baguettes a guesstimate would be that half of the shrinkage is due to cooling and half due to degassing. Only way to be certain would be to take a sample and put it under a good microscope and check for vesicles.
Geological fun in a tube
If you take a closer look at the both the tube walls and the magma baguettes you will notice a few things. First of all the baguettes show a coating of rust, second of all you will notice that the walls look sparkly and like they are covered with a semi-crystalline layer. To get a good grip on this we will have to travel to the coldest city on the planet.
In Norilsk you find the focal point of the Siberian Trap Formation. As enormous amounts of lava came to the surface lavatubes quickly formed, and as magma travelled through them for years or decades minerals was emplaced on the tube walls as the magma crystallized. In the case of Norilsk the magma had a core/mantle boundary origin and contained large amounts of nickel. The huge Norilsk lavatubes have walls covered with several meter thick layers of nickel ore. I can’t be certain, but judging from the rusty surface of the baguettes and the look of the walls on the photographs by Vitton Georges I would not be surprised if we are looking at another nickel deposit, albeit on a much smaller scale. If so it would be fun since the magmatic origin is believed to be quite different than in Norilsk.
Why do I call the baguettes magmatic and talk about magma instead of lava? Well, technically the material has never erupted, and as such it is still magma and not lava. You should though keep in mind that some ultra-purists would argue that it has degassed and as such can’t be magma.
VITTON GEORGES, PHOTOGRAPHY