What is the difference between pyroclastic flows and lahars

The difference between lava and pyroclastic flows lies on its speed. Lava creeps slowly and burns everything in its path but pyroclastic flows destroys nearly everything by land and air, its speed is usually greater than 80 km per hour, but it can reach km per hour. Lahars are flows that contain fragments of volcanic rock, they are the product of erosion on the slopes of a volcano.

These move fast , and can incorporate water, in such a way they form a mud flow. After this catastrophic event, the capital of Guatemala is in alert as the volcanos Fuego, Pacaya and Santiaguito have increased their activity, throwing lava and ashes.

In addition to the lahar, heavy rain made things worse, tearing down trees and increasing the flow of the Panaleon River. The death toll caused by the volcano has been rising since the eruption and if appropriate measures are not taken, it can continue affecting the surrounding communities.

In Guatemala, early warning systems are indispensable thanks to the multiple risks of natural disasters to which it is exposed. However, these systems are not as developed as in other countries. According to Juan Carlos Villagran of the Center for Research and Mitigation of Natural Disasters, all early warning systems, in particular lahars, should be strengthened and the evaluation of risks must be improved to avoid possible damage. Pyroclastic flows move fast and destroy everything in their path.

Fritz, A. Guatemala volcano killed dozens with its pyroclastic flows. Retrieved from: Washington Post. A tragic example of such an event was the eruption of Mt. Pinatubo in the Philippines, which was contemporaneous with the arrival of a major hurricane. An estimated people died from buiral by the ensuing lahars, together with the collapse of structures benearth the wet ash. As demonstrated by the graph below, lahars can also be generated directly from a volcanic eruption as massive amounts of water are generated either by the rapid melting of ice and snow, or by the disruption of crater lakes.

This graph demonstrates the number and type of volcanic events known to have produced lahars. It is based on a USGS study of historic eruptions from around the world. Modified from USGS. Pyroclastic flows are particularly efficient at generating lahars because they have the capability to melt large quantities of snow and ice in a just few hours. A tragic example of this mechanism occurred in when pyroclastic flows erupted at the snow-covered summit of the Nevado del Ruiz volcano in Columbia.

As the deposits built up they blocked the exit from the lake causing the water level to rise by a massive 60m and trigger fears of another disaster waiting to happen. Lahars are volcanic mud flows created when pyroclastic flows become mixed with water.

The ash and water mix and can form a type of mud that sets like concrete once it stops flowing. Water can come from within the volcano or surrounding area as the ground explodes and is pulverised, or from the melting of snow and ice on the flanks of the volcano.

The mud flows moved through houses picking up cars, trucks, trees and even whole buildings. The collected debris was carried downstream where it smashed into river defences and bridges. As the mud settled in the Columbia river it reduced the depth in places from over 12m to neared 4m, trapping large boats upstream of the shallows.

When Vesuvius erupted in AD79, Pompeii was buried under ash, but the nearby town of Herculaneum was hit by a lahar that totally buried the town. When it stopped flowing it set, literally as hard as rock. Today, both towns have been partially excavated, but Herculaneum is surrounded by high rock walls on top of which is a modern town. The rock walls are the exposed lahar into which archaeologists have dug to expose the ruins.

Lahars do not always occur at the same time as volcanic eruptions, and can occur at anytime where suitable deposits of ash and loose rock exist. This makes it almost impossible to predict a lahar.