Mount Usu

The Usu

Tōyako Onsen before of 1910 Kryptodom Meiji Shinzan

Mimatsu Masao - Denkmalbdep2

Area of the outbreaks of 2000 ( Low 2001) bdep3

The Usu (Japanese有 珠 山, Usu -zan ) is stratovolcano on the island of Hokkaido in northern Japan. The eruptions of Usu were formed repeatedly Lava Dome and krypton.

Construction

The Usu lies on the southern edge of the 10 km by measuring Toya Caldera, which originated around 110,000 years ago. In the presence of large parts of the caldera are occupied by Lake Toya. After formation of the caldera eruptions of basalt and andesite created a stratovolcano, designated according to the Vesuvius as Uso Somma. A violent eruption about 7,000 to 8,000 years ago destroyed the summit of the Uso Somma. It went from a debris avalanche, the deposits are south-southwest of the volcano to find on the coast of the Pacific Ocean. The eruption left a crater about two miles in diameter. Subsequent eruptions filled the crater largely with lava domes and krypton. The domes are made of dacite, a particularly viscous type of magma.

Outbreaks

Between 1663 and 1853 there were four Plinian eruptions with thicknesses from four to five on the Vulkanexplosivitätsindex ( VEI ). In this time in the crater of Kryptodom Ogari -yama lava domes and the Ko - Usu and O- Usu, with 733 meters the highest point of the volcano. During an outbreak in May 1822 Abuta village was destroyed. In this case, 50 people died, 53 were injured.

The outbreak from the July 25, 1910 went for six days ahead of earthquakes. At the same time formed at the northwest foot of Usu cracks and warping. Until the beginning of August, there were phreatic explosions of small, emerging craters. On the shores of Lake Toya, a new Kryptodom, the Meiji Shinzan (42 ° 34 'N, 140 ° 50' O42.560376140.836593252 ) was born. By November 1910, he arched up to 160 meters. Shortly after the outbreak of the first hot springs originated southwest of the Toya Lake. 1919 a hotel was built at a source. It paved the way for the emergence of the famous resort Tōyako Onsen.

Started at the end of 1943 a series of earthquakes whose epicenters shifted with decreasing amount of source depth at six kilometers from the northeast to east side of Usu. Beginning in February or March 1944, a further Kryptodom, the Showa Shinzan (42 ° 33 'N, 140 ° 52' O42.542545140.864348398 ) was formed about two kilometers east of the Usu- crater. He insulated from a river and broke through early November 1944, the earth's surface, which makes it the lava. Its growth ended in September 1945 after elevations of over 200 meters. Probably due to the cooling of the magma, the Cathedral 1945-1968 dropped by 25 meters. As of June 1944, the growth of the dome was accompanied by eruptions, where it phreatic first, later came to phreatomagmatic explosions.

The outbreak in the final stages of World War II was initially received little attention from researchers. Mimatsu Masao, a postal worker from Tōyako, the growth of the dome held firmly detail in images and reports. It was - as the geologist Hans Pichler - " an excellent volcanological work of a layman ." At Mimatsu Masao remember a museum and a monument at Usu.

An eruption on August 7, 1977 forced the evacuation of 20,000 tourists and 7,000 residents. At the outbreak of at least ten mile-high eruption column rose to; Ash fell on large parts of the island of Hokkaidō. Accompanied by weaker eruptions arched in the central crater another Kryptodom up to 180 meters on. The northern crater rim shifted to a similarly large amount. This resulted in Tōyako Onsen dislocations and cracks, damaged the homes and power lines or destroyed. In November 1978, caused a stream of mud, called a lahar, more damage to homes in Tōyako Onsen. Three people died.

On 31 March 2000, there was a flank eruption in the northwest of Usu. It broke the contact between an aquifer, which is fed by Lake Toya, and ascending magma heavy phreatomagmatic eruptions. By mid- April, more than 50 new crater formed. In the same month, lahars that caused damage in Tōyako Onsen and poured itself into the Lake Toya formed. The northwest of the Usu raised by up to 3.3 meters per day. The weaker eruptions ended in early May 2000. A day before the eruption from March 31, 10,000 people had been evacuated.