is an active volcanic group

Volcanic group

A volcanic group is a collection of related volcanoes or volcanic landforms. Note that the term is also used in a different sense when it denotes a suite of associated rock strata largely of volcanic origin; see group for details.-Notable volcanic groups:-See also:*Complex...

 of several overlapping stratovolcano

Stratovolcano

A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...

es, near the city of Shimabara

Shimabara, Nagasaki

is a city located on the north-eastern tip of the Shimabara Peninsula, facing Ariake Bay in the east and Mount Unzen in the west, in Nagasaki Prefecture, Kyūshū, Japan.-History:...

, Nagasaki Prefecture

Nagasaki Prefecture

is a prefecture of Japan located on the island of Kyūshū. The capital is the city of Nagasaki.- History :Nagasaki Prefecture was created by merging of the western half of the former province of Hizen with the island provinces of Tsushima and Iki...

, on the island of Kyūshū

Kyushu

is the third largest island of Japan and most southwesterly of its four main islands. Its alternate ancient names include , , and . The historical regional name is referred to Kyushu and its surrounding islands....

, Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

’s southernmost main island.

In 1792, the collapse of one of its several lava dome

Lava dome

|250px|thumb|right|Image of the [[rhyolitic]] lava dome of [[Chaitén Volcano]] during its 2008–2009 eruption.In volcanology, a lava dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano...

s triggered a megatsunami

Megatsunami

Megatsunami is an informal term to describe a tsunami that has initial wave heights that are much larger than normal tsunamis...

 that killed about 15,000 people in Japan’s worst-ever volcanic-related disaster

Disaster

A disaster is a natural or man-made hazard that has come to fruition, resulting in an event of substantial extent causing significant physical damage or destruction, loss of life, or drastic change to the environment...

. The volcano

Volcano

2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

 was most recently active from 1990 to 1995, and a large eruption in 1991 generated a pyroclastic flow

Pyroclastic flow

A pyroclastic flow is a fast-moving current of superheated gas and rock , which reaches speeds moving away from a volcano of up to 700 km/h . The flows normally hug the ground and travel downhill, or spread laterally under gravity...

 that killed 43 people, including three volcanologist

Volcanologist

A volcanologist is a person who studies the formation of volcanoes, and their current and historic eruptions. Volcanologists frequently visit volcanoes, especially active ones, to observe volcanic eruptions, collect eruptive products including tephra , rock and lava samples...

s.

Currently its highest peaks are at 1359 metres (4,458.7 ft) and at 1486 metres (4,875.3 ft).