If you don't already know, there are precursors to a Volcanic eruption. From an inflation of a volcanoes flanks, to a change in gas levels given off, to producing earthquakes with different frequencies and causes.
Today, scientists have revealed further signals that come before an eruption by looking at the earthquakes further. There are two main types of earthquakes produced from a volcano, ones that are caused from the fracturing of rock as the magma pushes upwards and ones that are caused from the vibration of magma as it rises through these cracks. The latter are more common at a later stage, closer to the eruption, seen on a seismograph as a long and gradual wave. The fracturing quakes are much shorter and start of with a sharp movement.
Scientists have been studying the volcanic eruption at Redoubt, Akaska. They found that these later stage earthquakes change from a steady drum beat to an increasingly rapid succession of tremors. It was described as a sound rising from one pitch to another which stopped just before the eruption. There analysis of these eruptions have seen that volcanoes can produce earthquakes to much higher frequencies and stop abruptly minutes before the eruption. These occur on the more explosive seen around the world.
The scientists involved, have described as this phenomenon as a scream!
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