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How do volcanoes cause tsunamis?

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 tsunamispercentage

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



Now read more hubs on tsunamis and volcanoes

  • What causes a Tsunami?
    Tsunamis are a natural disaster with devastating effects. Here you'll find a detailed breakdown of what causes a tsunami, which is perfect for school projects and essay answers.
  • What are the effects of a tsunami?
    Simply devastating. Homes can be wrecked, people can be killed, businesses destroyed and the psychological scars can last for generations.
  • What causes a volcano to erupt?
    Volcano eruptions produce stunning scenes of fiery lava shooting up from the depths of the earth. There are thousands of active volcanoes in the world - find out how they are formed and which will erupt next.
  • The biggest tsunamis in history: Lituya Bay, Alaska, 1958
    The biggest tsunami ever was caused by an enormous 8.3 magnitude earthquake in Alaska on July 9, 1958. A landslide of rock fell into a lake and caused a wave bigger than the Empire State Building. Read more...
  • Tsunami warning systems: Precautions used to predict deadly tidal waves
    Tsunamis have been happening for millions of years but in recent years by monitoring seismic activity under the sea it has become possible to predict when they will happen. Sometimes though, even the world's most advanced technology has its pitfalls.
  • Japan 2011: The tsunami that caused a nuclear meltdown
    The tsunami that hit Japan in March 2011 caused widespread devastation, but also threatened one of the worst nuclear meltdowns that the world has seen in decades. Six months on, the country is still struggling to contain radiation levels at the damag
  • How to survive a tsunami: A guide to escaping a natural disaster
    There are lots of steps people can take to ensure that they survive a tsunami if and when they hit. Even if someone is caught up in the water, there are things they can do to save themselves and others.
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Lucy Vincent on August 05, 2018:

I love tsunamis

SO MUCH!!!!!!!!!!!

ollllol on May 03, 2018:

good evdince

Kristen Howe from Northeast Ohio on February 28, 2018:

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

LOLKMANY321890 on November 05, 2014:


twitter syss on February 08, 2013:

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.

shanshi on February 07, 2013:


Mackenzi on January 04, 2013:


Ellen from California on April 06, 2012:

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.

malvika on February 23, 2012:

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

Joan Whetzel on November 25, 2011:

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

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