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How do volcanoes cause tsunamis?

Updated on November 24, 2011

A tsunami is a powerful wave that hits land. The effects of the tsunami in the worst cases can be devastating. Homes are wrecked and people are killed.

The most common cause of tsunamis is earthquakes. But volcanoes, another peril of the natural world, can also cause tsunamis. Volcanic tsuamis are not as common as earthquak tsunamis but when they do happen, their effects can be terrible.

There are two ways that volcanoes can cause tsunamis, or tidal waves as they are also known. The first way is from an eruption at a volcano on the land and the second is through an under water eruption from a 'submarine' volcano under the sea.

Let's first examine how land volcanoes cause tsunamis. (To fully see how nature and natural disasters interact you might also like to look at the hub 'what causes a volcano to erupt').

A volcanic eruption takes place when pressure in magma below the surface of the earth has been building up for some time. Eventually the magma breaks through the earth's crust and rushes to the surface through the volcano. This happens at subduction zones in the earth's surface, a region that has now become known as the 'ring of fire' because there have been so many volcanic eruptions here.

When the eruption happens, the top of the volcano, also known as the crater, is smashed open. The lid is literally blown off by the force of the magma. This causes large parts of the volcano to become dislodged. When the volcano is next to the sea, the debris comes crashing down into the water. The lava often also runs into the sea and large volumes of water are then displaced.

Clouds of ash surge into the air following an underwater volcano explosion
Clouds of ash surge into the air following an underwater volcano explosion
An underwater volcanic explosion, the type of which can lead to tsunamis
An underwater volcanic explosion, the type of which can lead to tsunamis
A woman with her face covered walks away from a land volcano that caused a tsunami
A woman with her face covered walks away from a land volcano that caused a tsunami
Lava is spewed from an erupting volcano
Lava is spewed from an erupting volcano

The effect of debris landing in the sea is the same as dropping a large brick into the bathtub when it's full of water. There are big ripples and everywhere gets soaked. This also happens in the sea. Powerful seismic waves are created and they travel across the ocean. This is the beginning of a tsunami.

The energy of the waves continues travelling through the sea. We know from science classes that energy cannot be created or destroyed, it is simply passed on. And so the wave continues through the sea until it comes into a coast. There the water is shallower and the seismic waves beneath the surface become large, powerful tidal waves that swamp the shore and crash onto buildings, causing all the disastorous effects we associate with tsunamis.

The second way that volcanoes can cause tsunamis is when they are underwater, also known as 'submarine' volcanoes or offshore volcanoes. Submarine volcanoes can be found by the presence of high rock content and steam above water surface. These submarine volcanoes form high slope pillars over their craters, a feature that is often absent in land volcanoes.

The volcanic eruption under the sea can produce high magnitude lifts on the seafloor. This is coupled with lava being forced out into the water. The lava quickly solidifies and turns to rocks. Such an eruption is an explosive interaction between water and magma, which produces fine grained tephra with the emission of magmatic gases and steam.

The eruption causes diruption in the earth and pushes large water columns upwards to generate tsunami. The explosion into the sea also displaces large volumes of water, causing underwater seismic waves.

As was explained above, these water waves have very high frequency and very small wavelengths when they reach land. This results in the tsunami.

Cause of volcanic tsunamis
Earthquakes accompanying eruptions
Pyroclastic flows impacting on water
Submarine explosions
Caldera collapse or subsidence
Avalanches of cold rock
Base surges with accompanying shock waves
Avalanches of hot material
Air-waves from explosions
Lahars (mudflows) impacting on water
Lava avalanching into the sea


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    • Kristen Howe profile image

      Kristen Howe 7 weeks ago from Northeast Ohio

      This was real informational and good to know about this type of topic. Thanks for sharing.

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      lol 2 years ago

      great!!!!!!!!!thx for the info;)

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      LOLKMANY321890 3 years ago


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      twitter syss 5 years ago

      the volcanoes are the most devatating natural disasters it is unbearable to see the burnt bodies of humans and animals .volcanic eruptions are useful for us but at the same time it is more dangerous .so please pray god for to stop it totally where there is a habitat.

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      shanshi 5 years ago


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      Mackenzi 5 years ago


    • Greekgeek profile image

      Ellen 6 years ago from California

      Did you see recent research showing that most of Molokai must have collapsed into the sea in one HUGE tsunami, after the old volcano there eroded? The amont of debris on the sea floor north of the island is just enormous.

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      malvika 6 years ago

      It is very interesting i learn't so much things through this and thankyou so much

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      Joan Whetzel 6 years ago

      Great description. I love learning new-to-me things like this.