On air broadcast delivered by Dr Shane on Sunday 13 April, 2008.
Online article written by Michelle Kovacevic.
JUST WHEN YOU THOUGHT that global warming was causing enough problems, it seems that European scientists are about to add another cross to its name.
Scientists have calculated the effects of melting ice caps on the Earth’s crust and underlying magma and have found that magma melts faster as the pressure exerted by the solid ice sheets decreases.
This has a potentially serious effect on the risk of volcanic eruptions around the world. Magma (called lava once it rises to the surface) is molten rock that often collects in chambers beneath the surface of the Earth.
As the ice caps melt, the pressure exerted by the ice on the underlying rocks decreases and causes the occurrence of a process known as decompression melting. Every rock has a temperature below which it is solid (called the solidus temperature). This “melting” temperature decreases as the pressure is decreased therefore, theoretically, at a lower temperature, rock will melt more quickly, forming larger volumes of magma.
Carolina Pagli, from the University of Leeds and Freysteinn Sigmundsson of the University of Iceland have observed the rate of magma production occurring due to the melting of Vatnajökull, the largest ice cap in Iceland.
They found that an average of 1.4 cubic kilometres of magma has been produced every century since 1980, a 10% increase on the background rate. They say that this extra magma produced as the ice cap melts, could supply enough magma for large volcanic eruptions to take place every 30 years.
Explosive volcanic eruptions are driven by gases accumulating under great pressure. Hot magma rises through fractures in the mantle as it is less dense than the surrounding rock. As it rises, it interacts with ground water and the pressure increases until it explodes through the overlying crust, allowing molten rock, ash, and gases to escape.
Predicting whether particular eruptions will occur is quite tricky as the rate of magma migration to the surface is still largely unknown.
