A SWARM of shallow earthquakes beneath Mount St Helens in Washington state has prompted the US Geological Survey to warn of an 鈥渋ncreased probability of explosions鈥� from the volcano. Hiking trails on its slopes have been closed.
The first tremors were picked up on 23 September. Three days later, as the quakes intensified, the USGS issued a 鈥渘otice of volcanic unrest鈥�. The earthquakes are being triggered about a kilometre beneath the lava dome in the volcano鈥檚 crater, suggesting a build-up of water, steam or magma. Quakes of magnitude 2.8 were recorded on Sunday.
The mountain鈥檚 massive eruption in 1980, which left 57 dead, was preceded by an earthquake of magnitude 5.1 and two months of heightened seismic activity. Nothing so violent is expected this time round. 鈥淭he key issue is a small explosion without warning. That would be the major event that we鈥檙e worried about right now,鈥� Willie Scott of the USGS told Associated Press.
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