While many people are mesmerized by the idea of witnessing a volcanic eruption, the rising column of smoke and ash coupled with the glow of fiery rocks and lava pale in comparison to the event that happens as a result of the eruption. The real danger is what is not normally seen in the news footage. Anyone in place to get a good picture of it will be dead before the picture can be made. It is a lahar.
Lahars kill many more people than the flying debris from a volcanic eruption.
Because a lahar is a rapidly moving mass of superheated mud, water, rock, and more, it can destroy everything in its often miles long path. Reaching up to 200 feet in height, a lahar is frequently the ugly side of the pyroclastic flow. It can stream down the mountain at speeds exceeding 100 miles per hour. The steam and hot materials within the lahar crush and burn anything within its reach. The lahar is usually responsible for hundreds of times more casualties and damage than all of the rest of the losses caused by other dangers from the eruption combined.
The peaks of volcanos may either be a lake or a porous area filled with large amounts of water that is sometimes frozen.
When the huge shudders of the quakes that accompany a volcanic eruptions occur, this unstable material gives way into an avalanche. The heat pouring through the cone of the mountain turns this mud slide into a hot steam filled monster. The steep sides of the volcanic cone coupled with the force of the spewing eruption drives this pyroclastic flow at uncanny speeds toward certain death and destruction for anything below.
People cannot usually outrun a lahar.
Because volcanoes do not erupt every day, people begin to move in to live around and on them. These residents may be there for several years with no volcanic activity other than minor tremors. They are lulled into believing that when the eruption begins, they will leave. By the time that the enormous sound from the blast reaches their ears, only moments may stand between them and death. Just the time that it takes to flee their house and start their car may already result in their demise. Even if the car starts, unless they are prepared to drive 20 miles at 100 miles per hour, they still may not survive.
Lahars are little understood and hard to predict.
If a volcano has a crater lake, an eruption will usually break the dam and let loose a lahar. However, only a small percent of volcanoes have a crater lake. If they are ice tipped, it is a good bet that enough moisture is present to fuel a lahar. The reality is that the violence of a volcanic eruption is so severe that even mountains that are not known to be prime lahar candidates often produce one. The best idea is to avoid living within range of a lahar. If you insist on doing so, leave at the first hint of trouble. Any delay could be fatal.
Resource:
http://www.answers.com/topic/lahar
