How does a seismograph predict voloanic eruptions?

Question

I need to know how a seisemograph can dectect and record lava flows to predict when a volicano will erupt

Answer 1

As the magma moves up into the chamber of the volcano it puts a massive about of pressure on the surrounding rock. As these EQ's get more shallow (closer to the surface) this indicates the magma is moving up. The frequency, strength and duration of these mini EQ's will give the scientist an idea of how much and how fast the magma is moving. Also if they are lucky enough to have several stations they might be able to use the quakes to build up a sort of x-ray of the chamber and how big it is. this will also indicate that possible size of the eruption.
The thing is all they can do is make a best guess. The study of volcanoes though old has lots of catching up to do to the rest of prediction science(not that they are perfect with weather either). Its not exact but we are better off today then even 10 years ago.

Answer 2

A seismograph is only one tool scientists are using, in an attempt to LEARN how to predict volcanos and earthquakes. If the technique had already been developed, then many lives would have been saved in the last several years.

What a seismograph detects is the movement of ground in the area of the instrument. They are pretty sensitive and can detect, even very slight movements, such as the passing of nearby automobiles, and, man made explosions many miles away. SOME of these movements can detect imminent volcanic activity, but, scientists do not, yet, know exactly which of these tremors mean eruptions, and which are, merely, earthquakes.

What the instuments CAN do is give scientists warning that SOMETHING is going on, and, in the vicinity of an existing, active volcano, people can be advised to move out of the area, just in case.

In the massive eruption of Mt. St. Helens, in Washington state, geologists' instruments detected movement, and many speculated that an eruption could occur very soon. Many people were warned, but, because the predictions were, as yet, still unreliable, some people ignored the warnings and stayed put.

One can think of such seismographic warnings as being similar to some storm warnings. The signs may indicate a potential for severe weather, with greater and lesser degrees of possibility, but one can never be sure, until the event is very, VERY close.