Updated: Jun 22
I have just spent a week on a geology field trip in Iceland and thought I would post some photos that may be of interest to some Chimp Investor subscribers and visitors.
An exposed section of a cinder cone. You can make out the regular layers of pyrorclastic material (ash) that built up on the sides of the cone. It is possible that the entire chunk of rock slipped down the slope as material underneath it was eroded - other chunks that slipped down may have broken up and been eroded away and others still remain in place (you can see some exposures near the top of the ridge).
Almost all rocks in Iceland are basaltic meaning that the lava or magma from which they were formed came from the mantle rather than the crust. Because basalt comes directly from the mantle it does not contain gases that inhabit the crust which when incorporated in crust-derived magma cause eruptions to be explosive (analogy = taking the top off a shaken fizzy drink bottle). Thus basaltic eruptions tend to be effusive rather than explosive, unless they occur under ice as did the 2010 eruption that sent ash high into the atmosphere causing air traffic mayhem.
Lava that has been turned red by reaction with water, a process known as rubefaction.
When basalt lava erupts into water at the bottom of a sea or lake it forms pillow shaped structures called pillow basalts. The surface of a molten "pillow" is cooled quickly by the water and forms a fine-grained red/brown shell. The molten interior of the pillow cools more slowly and does not react with the water. As a result it contains radial fractures and is not red/brown.
The North American tectonic plate is on the right, Eurasian to the left. The plates are being rifted apart as ocean crust thousands of miles away around the Pacific is pulled back into the earth. Normally, these gullies (faults) are parts of huge, long mountain ranges at the bottom of oceans called mid-ocean ridges, but a mantle plume (a cylinder of partially molten material welling up from deep in the mantle) has pushed up/kept a small part of the mid Atlantic ridge above sea level that we call...Iceland.
Another gully (fault), this time in the graben (an extensional valley) in the Pingvellir area, but one in which one can snorkel/dive.
View to the west along the Reykjanes Penninsular. Turn around and you see...
...this. The cone is one of several (you can see others in the distance) that make up the Fagradalsfjall volcano which started erupting on 19 March last year and which was active for six months. The Icelandics quickly built levees to divert the flows, fearing the eruption might produce as much lava as the 1783-4 Laki eruption and destroy roads and other property. The Laki eruption certainly produced lava flows that were directly destructive but its far more serious impact was in relation to food supplies, both locally and across Europe, that were impacted by volcano-induced acid rain and falling temperatures. A quarter of Iceland's human population died and crop failure is believed to have played a role in triggering the French Revolution.
Closer up. The yellow areas are sulphur from hydrothermal activity percolating up through the flow. The lava has a ropey texture and is called pahoehoe. When it is more viscous it has a rubbly texture and is called aa. Both Hawaiian words.
Downstream. The cone in the two previous photos is above the flow in the top left of the photo. In total the flow is several kilometeres in length.
The remains of the side of a lava channel formed when Búrfell volcano south east of Reykjavik erupted around 8,000 years ago. The layers on the outside of the channel wall (to the right) are formed when lava overflows the top of the wall. Layers are progressively built up as the height of the lava flow and thus the channel walls rise.
There is so much else in Iceland of geological interest and of interest in other areas, natural and otherwise. It is well worth the generally high prices.
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