An earthquake, recorded…The layers in this rock are called varves, and form when rhythmic con

An earthquake, recorded…The layers in this rock are called varves, and form when rhythmic conditions control sedimentation. An example would be the bottom of a mountain lake that gets covered in ice during the winter. The coarser grained layers might be brought by streams flowing into the lake during spring thaw and through the summer, carrying the winter’s worth of erosion load after its cycles of freeze thaw and grinding ice. The finer grained darker sediments would then slowly settle out of suspension when the turbulence of the streams or wind caused waves are quashed by father frost and the lake settles into quiescence.The name comes from the Swedish word for ‘in layers’, and while it technically means annual sedimentary rhythms, the use has widened somewhat to include any rocks displaying seasonal cyclicity, or even sometimes daily. They only form in fresh water, as too great a salt content coagulates the particles of clay together, destroying the sedimentary record. Varved lake sediments are very useful in reconstructing past climates and record some of the shortest time intervals in the geological record. Chemical and isotopic analysis of the sediments allows us to tell past temperatures and other information about long gone weather patterns.This example is even more exciting, recording a quake near the Dead Sea in Israel, that shook the layer deposited in that particular year and deformed it in a manner reminiscent of the large scale fractal version of this process that occurs during mountain building events as rocks are baked and squished towards gneiss. The Dead Sea is a graben, where a large chunk of rock has dropped down in between two bounding faults (see http://on.fb.me/1Kj8ies). Since Arabia is separating from Africa at the Red Sea and bumping into Asia, powerful tectonic forces are being redistributed across the region. As a result of all this excitement quakes are fairly frequent in the region.LozImage credit: Hebrew Wikimedia Commons/ http://bit.ly/1LUBJmm -- source link

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