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 emission
- Lahars
- Ash columns and flows
- Lava flows
- Earthquakes
- Tsunamis
- Landslides
Ash Columns and Pyroclastic Flows
Ash columns and ash flows are produced when a volcanic eruption is extremely explosive. Many of the volcanoes of the world, especially those near subduction boundary zones, eject silica-rich magma. This type of magma is gas rich and very viscous, so when it erupts it is explosive. The high explosiveness of the eruption shreds chunks of the magma as is solidifies, producing microscopic pieces of silica glass, or ash.
Ash columns and ash flows, or pyroclastic flows, are two hazards produced when a volcano ejects ash. An ash column is characterized by the ejection of ash straight up into the atmosphere. This type of hazard can be dangerous to humans on the ground and to aircraft in the sky. A pyroclastic flow is characterized by the flowing of ash down the flanks of a volcano. Typically, this flow is produced by the gravitational collapse of an ash column but can also be produced just by the eruption itself.
Deadly Pyroclastic Flow
The 1980 Mt. St. Helens eruption produced both ash columns and pyroclastic flows, and the results were deadly. Even more deadly was the 1902 eruption of Montagne Pelee in the West Indies. When this volcano erupted it sent a wave of boiling hot gas and ash towards the peaceful village of Saint Pierre – a town precariously nestled on the lower flanks of the volcano – at speeds up to 310 miles per hour. Without any warning, this pyroclastic flow killed 27,000 people; practically the entire village. The sole survivor was found days later in an underground prison.
Lava Flows
Lava flows are produced by less explosive volcanoes. This hazard is typically produced by a volcano that has basaltic-rich magma. This magma degasses much more easily than its silica counterpart and is also less viscous, so it flows more easily. Hawaiian volcanoes, such as Kilauea Volcano, are famous for their beautiful, streaming lava flows. In many cases, these lava flows do not present a large threat and visitors to Hawaii Volcanoes National Park can walk right up to an accessible flow.
However, lava flows are an unstoppable force of nature, destroying property and causing land to be uninhabitable. They can start forest fires and release toxic gases as they flow down volcanoes. They destroy farms and force people to evacuate their homes, causing anguish and devastation that can be long-lasting.
Source: U.S. Geological Survey
