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This is to prove to myself that I retained some of what I heard on my vacation and that it did not all go in one ear and out the other.... I am going strictly on memory here, so I may get details wrongs.
Andesite is a volcanic rock that is formed when molten rock at the edge of subduction zones (where one plate dives under another, which causes the rock to melt) forces its way to the surface. Andesitic volcanoes (I'm not sure if that is the right word for them -- just how I think of them) tend to explode violently, a la Mt. St. Helens. Andesite is from lava which is exposed to the air and which therefore cools rapidly, resulting in a small, more irregular crystal structure. The name "Andesite" comes from the Andes mountains.
Granite is likewise formed at the edge of subduction zones. Unlike andesite, however, granite never breaks through to the air (it just sort of creates a "bubble" under the surface of the earth). As the subduction zone moves away, the granite cools. Because it cools more slowly than andesite, it has a larger, more regular crystal structure. Granite is exposed by weathering (such as by glaciers). Half-dome is basically a big honking piece of granite that was cut in half as glaciers moved down the Yosemite Valley.
Basalt is volcanic rock that is formed by lava welling up from the mantle (much deeper than andesite or granite). It is denser than andesite or granite. Basaltic volcanoes (again, I'm not sure what the technical term for them is) have lava flows rather than explosive eruptions.
Columnar basalt is formed under very specific conditions. There must be a pool of molten basalt to some depth. The pool must be in contact with the air and in contact with cooler bedrock. As the basalt cools, surface tension creates cracks in the rock. When a crack reaches about 10", it branches at a 120 degree angle. As the cracks propogate, they join up, forming polygonal patterns. Then cracks start to propogate vertically, joining the polygons at the top and bottom of the formation. The result are basically big polygonal columns. Examples of columnar basalt are Devil's Postpile in California and Devil's Tower in Wyoming.
Tufa, as is found at Mono Lake, is caused when calcium rich springs bubble up through carbonate rich lake water. The resulting calium carbonate is deposited in tower formations. In the case of Mono Lake, the tufa was under the lake surface, until predations by the Los Angeles DWP on the streams that feed the lake caused the level to fall precipitously over several decades and exposed the tufa towers.![[livejournal.com profile]](https://www.dreamwidth.org/img/external/lj-userinfo.gif)
joedecker has taken some stunningly beautiful pictures of the Mono Lake Tufa.
So,brian1789, do I pass?
Andesite is a volcanic rock that is formed when molten rock at the edge of subduction zones (where one plate dives under another, which causes the rock to melt) forces its way to the surface. Andesitic volcanoes (I'm not sure if that is the right word for them -- just how I think of them) tend to explode violently, a la Mt. St. Helens. Andesite is from lava which is exposed to the air and which therefore cools rapidly, resulting in a small, more irregular crystal structure. The name "Andesite" comes from the Andes mountains.
Granite is likewise formed at the edge of subduction zones. Unlike andesite, however, granite never breaks through to the air (it just sort of creates a "bubble" under the surface of the earth). As the subduction zone moves away, the granite cools. Because it cools more slowly than andesite, it has a larger, more regular crystal structure. Granite is exposed by weathering (such as by glaciers). Half-dome is basically a big honking piece of granite that was cut in half as glaciers moved down the Yosemite Valley.
Basalt is volcanic rock that is formed by lava welling up from the mantle (much deeper than andesite or granite). It is denser than andesite or granite. Basaltic volcanoes (again, I'm not sure what the technical term for them is) have lava flows rather than explosive eruptions.
Columnar basalt is formed under very specific conditions. There must be a pool of molten basalt to some depth. The pool must be in contact with the air and in contact with cooler bedrock. As the basalt cools, surface tension creates cracks in the rock. When a crack reaches about 10", it branches at a 120 degree angle. As the cracks propogate, they join up, forming polygonal patterns. Then cracks start to propogate vertically, joining the polygons at the top and bottom of the formation. The result are basically big polygonal columns. Examples of columnar basalt are Devil's Postpile in California and Devil's Tower in Wyoming.
Tufa, as is found at Mono Lake, is caused when calcium rich springs bubble up through carbonate rich lake water. The resulting calium carbonate is deposited in tower formations. In the case of Mono Lake, the tufa was under the lake surface, until predations by the Los Angeles DWP on the streams that feed the lake caused the level to fall precipitously over several decades and exposed the tufa towers.
joedecker has taken some stunningly beautiful pictures of the Mono Lake Tufa.So,
brian1789, do I pass?![[identity profile]](https://www.dreamwidth.org/img/silk/identity/openid.png){kind=small}
From:
Re: Cool stuff
From:
Re: Cool stuff