Why are geologists able to make long term but not short term predictions about volcanos?

Answer 1

Because they can measure the fact that pressure is building up inside, and sooner or later it is going to release. They just can't be sure exactly how much pressure it will take to make it blow, or if there could be a release of pressure through a steam vent or just a flow rather than a full eruption. But they know if it starts building pressure, it will have to do something. There are other factors too, like how porous the rock is, and how many air chambers there are and so on.

Answer 2

They can observe through siesmic techniques that lava is moving upwards but it becomes very difficult to predict when the eruption will occur because there is very little knowledge about the strength of the underlying structures and for example, the exact nature of the faulting. What might happen in a particular eruption is that the volatiles released by the upwelling magma gets trapped and this builds up pressure. When it gets released, it might end up in an explosion that is powerful enough to trigger the eruption or it might just let off some steam. There is never a case where there is perfect knowledge of the underground structures and materials.

Answer 3

We know that the prediction of volcanoes is done by averaging data about the geography of that area where the volcano is. To do this process geologists need a lot of time to collect data. And that leads to the long term predictions of volcanic eruptions.

Answer 4

The same reason a person can make predictions about the movement of a crowd without being able to predict accurately a single person in the crowd - large events are more likely to follow a pattern than small events will follow a schedule.
Without knowing when the second hand will point straight up, I can still predict that it will point straight up within 60 seconds.
Without knowing when the earth will shake, I can still predict that a fault will slip when tension gets great enough and since it is increasing, I can predict that it will occur within the next 5 years.

Answer 5

If you have a pimple starting to grow on your nose, can you predict when it will come to a head?... Well, geologists have the same problem, but on a lot bigger scale.

They can see the pressure building and the plates moving, but they don't know for certain when it will erupt...

OH... and you can squeeze a pimple.