Lava flows are the least hazardous of all processes in volcanic eruptions. How far a lava flow travels depends on the flows temperature, silica content, extrusion rate, and slope of the land. A cold lava flow will not travel far and neither will one that has a high silica content. Such a flow would have a high viscosity (a high resistance to flow). A basalt flow like those in Hawai'i have low silica contents and low viscosities so they can flow long distances. Such a flow can move as far away as 4 km from its source and have a thickness of 10 m (Bryant, 1991). These flows can move at rates of several kilometers per hour (Scott, 1989).
More silica-rich flows can move as far away as 1.3 km from their sources and have thicknesses of 100 m (Bryant, 1991). These flows can move at rates of a few to hundreds of meters per hour (Scott, 1989). If a lava flow is channelized or travels underground in a lava tube then the distance it travels is greatly extended.
Lava flows as you can see don't move very fast so people rarely get killed by them. However, lava flows are very hot (between 550 degrees C and 1400 degrees C) and can therefore cause injuries.
People have burnt their skin, charred
their eyebrows, and melted the soles of their boots from being near or on a hot lava flow. Lava flows don't cool instantaneously. It can take days to years for a lava flow to completely cool.
The biggest hazard of lava flows is that they destroy property. In the late 1980's, the town of Kalapana in Hawai'i was destroyed by lava flows. Lava flows buried cars and burnt homes, buildings, and vegetation. Electric power, water, and communications were cut off from the community.
Another hazard associated with lava flows (as well as other hot volcanic material) is they can melt snow and ice which can produce flooding. Melting of ice beneath a glacier may produce very large floods called jokulhlaups or glacier bursts (Bryant, 1991) Lava flows can also dam rivers which may in the future produce flooding if the dam were to break, though most lava flows are fairly porous (Scott, 1989).
The main concern with lava flows is how far they will ultimately extend. Equations have been used to estimate this distance (see Pinkerton and Wilson, 1994). But how do you stop a lava flow if you know it's heading toward your property? Different methods have been used including: breaching the sides of a lava tube or channel, diverting the flow, constructing barriers, and bombing the lava flow. Another way to stop a lava flow is to increase the lava flow's viscosity (Bryant, 1991 and Scott, 1989) by spraying it with water, increasing the rate at which gas escapes from the flow, stirring the flow, or seeding the flow with foreign nuclei (Bryant, 1991).
Text by C.M. Riley, Photos by C.M. Riley