Traditionally, scientists believed that all tectonic plates are pulled by subducting slabs -- which result from the colder, top boundary layer of the Earths rocky surface becoming heavy and sinking slowly into the deeper mantle. Yet that process does not account for sudden plate shifts. Such abrupt movement requires that slabs detach from their plates, but doing this quickly is difficult since the slabs should be too cold and stiff to detach. Each winter, sea ice expands to fill nearly the entire Arctic Ocean basin, reaching its maximum extent in March. Each summer, the ice pack shrinks, reaching its smallest extent in September. The ice that survives at least one summer melt season tends to be thicker and more likely to survive future summers. Since the 1980s, the amount of this perennial ice (sometimes called multiyear) has declined. In September 2012, Arctic sea ice melt broke all previous records. In recent decades, it has become apparent that the consequences of planetary ice loss might not end with rising sea levels. Evidence has been building that in the past, periods of severe loss of glaciers were followed by a significant spike in volcanic activity. Ice sheets are heavy. Each year, Antarctica’s loses around 40 billion metric tons of ice. The sheets are so heavy, in fact, that as they grow, they cause the Earth’s crust to bend – like a plank of wood when placed under weight. The corollary of this is that, when an ice sheet melts, and its mass is removed, the crust springs back. This upward flexing can lead to a drop in stress in the underlying rocks, which, the theory goes, makes it easier for magma to reach the surface and feed volcanic eruptions.
Posted on: Wed, 21 Jan 2015 00:55:46 +0000
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