is the name of a group of shield volcano

Shield volcano

A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior's shield. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from more explosive volcanoes...

es located on the coast of 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...

 on the southwest end of the island of Honshū

Honshu

is the largest island of Japan. The nation's main island, it is south of Hokkaido across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyushu across the Kanmon Strait...

. It is primarily based in the city of Hagi

Hagi, Yamaguchi

is a city located in Yamaguchi, Japan and was incorporated as a city on July 1, 1932. Formerly part of Abu District.On March 6, 2005, the former city of Hagi merged with the towns of Susa and Tamagawa, and the villages of Asahi, Fukue, Kawakami and Mutsumi to form the new city of Hagi.Iwami Airport...

, Yamaguchi Prefecture

Yamaguchi Prefecture

is a prefecture of Japan in the Chūgoku region on Honshū island. The capital is the city of Yamaguchi, in the center of the prefecture. The largest city, however, is Shimonoseki.- History :...

.

The group dates from 800,000 years ago and was active into the Holocene

Holocene

The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...

 era. The last eruption occurred around 3000 years ago.

The group of volcanoes consists of basalt

Basalt

Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...

 and dacitic lava flows, small shield volcanoes, cinder cones, and lava domes. Altogether, there are about 40 volcanoes, with the highest peak being Irao-yama.

Volcanic activity in the region is thought to be related to subduction

Subduction

In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...

 of the Philippine Sea Plate.