Volcanic Hazards & Prevention: Landslides, Lahars & Tsunamis

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  • 0:05 Volcanoes
  • 0:37 Volcanic Hazards
  • 1:41 Lahars
  • 3:09 Tsunamis
  • 4:10 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Volcanic hazards are any volcanic process that can damage property or threaten life. Learn about volcanic hazards, such as landslides that can trigger lahars and tsunamis, and ways to prevent these hazards from threatening people's lives.


Volcanoes can erupt with so much force that they eject small particles up into the stratosphere. Their destructive power can cause the area around the volcano to become uninhabitable, and even trigger ocean waves so large they can travel across entire oceans and destroy coastal areas thousands of miles away. In this lesson, you will learn about volcanic hazards that cause damage both at the site of the volcanic eruption and miles away, and get some insights into ways to prevent these hazards from harming people.

Volcanic Hazards: Landslides and Earthquakes

A volcanic hazard is any volcanic process that threatens life or destroys land or infrastructure. When you think of a volcanic eruption, you may get a picture in your head of red-hot lava rushing down the slope of a volcano, and while this is perhaps the most remarkable feature of a volcano, lava is not the only hazardous material to fall from a volcano.

A landslide is a mass movement of rock fragments, soil and debris downslope. Landslides can happen at any mountain where the slope of the mountain has become less stable, but they are commonly associated with volcanic activity because the volcanic mountain is weakened by the magma and pressure brewing inside. For example, magma can get injected into volcanic rock and the sides of the volcano as it rises toward the surface. This can weaken the slopes of the volcano, leading to a landslide.

It can also lead to a volcanic earthquake, which is an earthquake induced by the pressure and stress of volcanic activity. Volcanic earthquakes can then trigger landslides.


Landslides create a number of hazards to people and property because they have a potential to travel long distances, and they pick up momentum and speed as they travel down the slope of a volcano, with the ability to travel at more than 50 miles per hour. The debris that's carried in a landslide destroys anything in its path, buries valleys in rock and debris and can dam waterways, leading to flooding.

If the debris within the landslide mixes with enough water, the landslide can turn into a lahar and continue to travel for miles. A lahar can be defined as a flowing mass of volcanic debris and water. A lahar resembles a river of wet cement flowing down a volcano and into a valley.

They vary in speed depending on the amount of water and the size of the debris being carried in the flow. The wettest lahars travel tens of meters per second, making them impossible to outrun. Therefore, lahars are extremely dangerous and destructive for communities living downslope of a volcano.

Some communities have built structures around their living areas to act as barriers to the flow of lahars and prevent destruction. However, the best preventative measures are to be prepared with evacuation routes for citizens of the communities and the development of a warning system that can detect if conditions are wet enough to support a lahar or to detect seismic signals of a lahar barreling down the valley.


Another volcanic hazard that can be triggered by a landslide is a tsunami. A tsunami is a series of large ocean waves caused by an abrupt disturbance, such as a landslide. A tsunami travels quickly in deep ocean waters, reaching speeds of more than 500 miles per hour, which means it could outrace a jet plane.

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