Volcanic Eruption Signals Help (page 2)

Eruption Signals

Volcanoes are fairly “iffy.” If we look at all the recorded eruptions over the centuries, we would find that some smoldered for months to years, while others gave no notice at all before belching out with deadly menace. The only reliable predictor of volcanic eruptions seems to be the response of the animal kingdom in the hours before an eruption. Tuned into some sixth or intuitive sense, they seem to know something big is about to happen. But short of keeping your pets nearby all the time, how can humans predict a volcano’s misbehavior in time to get clear of the danger?

Geologists use a number of instruments to record the moods of volcanoes and predict their activity. Lasers are used to measure the distance across the crater of a volcano and its growth.

Seismographs measure vibrations in the earth from earthquakes. They detect and locate small earthquakes that geologists correlate with magma movement.

Scientists have used seismographs to identify earthquakes as deep as 55km beneath Kilauea and Mauna Loa of Hawaii. Earthquakes can signal the movement of magma into vents and channels leading to the surface. Hot magma can take months to move upward. However, when a volcano awakens from a long sleep, there is intense and almost constant seismic activity. When something major is about to happen, seismographs go wild in the days and hours just before an eruption. It becomes clear that an eruption is about to happen when a mob of earthquakes, thousands of them, signal that pressurized magma is splitting solid rock on its driving sprint to the surface.

Volcanoes are classed into 3 types: active, dormant, or extinct.

A volcano is considered active if it has erupted within recent recorded history. If a volcano has little erosion and looks fairly fresh, it is considered dormant with the ability to become active again at any time. If a volcano has not erupted within recorded time and is eroded to a large extent, it is thought to be extinct and very unlikely to erupt again.

However, these are just “rule-of-thumb” activity terms that volcanologists are still working on. The frequency of eruption of volcanoes can be very unique. An average volcano has been found to erupt once every 220 years, but 20% of all volcanoes erupt only about once every 1000 years, and only 2% erupt less than once in 10,000 years. So just because a volcano has been sleeping a very long time, there is no guarantee it will never erupt again!

There are nearly 600 active volcanoes on the planet today. Of these, 17% have been human killers. Roughly 200,000 people have been killed by volcanic eruptions in the past 500 years.

Volcanoes do this in the following nasty ways, either separately or in combination:

(a) Explosions

(b) Fiery ash

(c) Toxic gases

(d) Lava flows

(e) Mud flows or lahars, and

(f) Building collapse.

Luckily, of the 100 highest-risk active volcanoes in the world, only about of them erupt every year. Unlike ancient people, we are a lot more prepared. Today, volcanologists’ increased use of land and space-based technology has improved our odds of predicting and surviving eruptions.

Active volcanoes are those that have erupted within recent (recorded) history. Table 11-4 gives a list of volcanic eruptions that occurred in the past 300 years around the world. The biggest or latest eruptions are given. Active volcanoes are classified as Types I through V depending on their activity levels and rate of eruptions.

Table 11-4 Major volcanic eruptions have been recorded for over 300 years.