Volcanic Hazards: Gases and Lahars
One Volcano Can Produce a Variety of Hazards
Volcanic activity can produce toxic gas, lava flows, lahars, and earthquakes. History shows us that these hazards can by deadly.
One volcano can produce a variety of volcanic hazards when erupting. Some volcanic hazards can happen when there isn’t even an eruption. The more that is known about volcanic hazards, the better prepared communities, who are at risk from these hazards, can be.
There are seven types of hazards associated with volcanoes:
- Toxic gas emissions
- Lahars
- Ash columns and flows
- Lava flows
- Earthquakes
- Tsunamis
- Landslides
Toxic Gases
Toxic gas emissions are produced when magma rises and gases that are trapped within the magma at depth are released. It works very similarly to carbonation being released when a bottle of soda is opened.
The two most common gases released when magma ascends is sulfur dioxide and carbon dioxide. Sulfur dioxide can float high into the atmosphere and mix with water vapor to form sulfuric acid. When it rains, this sulfuric acid comes down with the rain, ruining crops and destroying farms. Carbon dioxide can be lethal to humans and livestock, as it is heavy and usually stays close to the ground.
One of the most tragic cases of magmatic degassing resulting in deaths was the 1986 incident at Lake Nyos in Africa. Lake Nyos was a crater lake and magma had been degassing carbon dioxide into the lake for quite some time. Then, suddenly on August 12, new volcanic unrest caused carbon dioxide to be released from the lake all at once.
The carbon dioxide crept down the flanks of the volcano while villagers at the bottom of the volcano slept. When the morning arrived, approximately 1,700 villagers had died of asphyxiation from carbon dioxide poisoning in their sleep.
Lahars
Lahars, or volcanic mudflows, can be equally as lethal – not just because of their far-reaching effects, but also because they can come with little or no warning. Lahars are caused by the mixing of volcanic material, such as fine ash and larger volcanic pumice stones, with water. The source of the water can be either heavy rainfall, or the melting of snow at the summit crater caused by an eruption. Lahars can travel great distances at incredible speeds, following drainage paths carved into the volcano and flowing over surrounding low-lying areas.
In November of 1985, Nevado Del Ruiz (“nevado” meaning “snow covered”) Volcano in Columbia began to show signs of unrest. Volcanologists were concerned about the possibility of a lahar and urged surrounding towns to be prepared for an evacuation.
Unfortunately, the lahar came sooner than preparations could be organized. On the night of November 13, a small and otherwise insignificant eruption occurred at the summit of the volcano. The heat generated by this small eruption was enough to melt substantial amounts of snow on the volcano.
Without any warning, a very dangerous lahar was being created and making its way quickly down the volcano towards the city of Armero. The only warning that the sleeping residents of Armero had was the incredible noise the lahar made as it swept through the town, destroying homes and killing more than 23,000 people in one night.
Source: U.S. Geological Survey
