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Topics: Volcanology glossary | Earthquake glossary

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Ubehebe Craters (Volcano)

Ubehebe Craters volcano is a group of maars (explosion craters) located at the western margin of Tin Mountain, California, in the northern end of Death Valley. The craters were thought to have last erupted about 6000 years ago, but a recent study suggests that some activity could have occurred as little as 800 years ago. -> See whole entry

Ubinas (Volcano)

Udokan (Volcano)

The Udokan Plateau volcano is a volcanic field located in southeastern Russia 400 km ENE of the Baikal Lake. The field contains cinder cones, lava domes, lava flows and explosion craters (maars). The latest eruption took place at Chepe volcano about 2200 years ago. -> See whole entry

Uinkaret (Volcano)

The Uinkaret volcanic field is located at the north rim of the Grand Canyon in Arizona. It contains cinder cones that have produced lava flows that repeatedly cascaded into the Grand Canyon, forming temporary lava dams up to 200 m high. In one of these lava flows, known as the Little Springs flow, pottery sherds were found that date to between 1050 and 1200 AD giving the age of the lava flow. -> See whole entry

Ulawun (Volcano)

Ulawun (also locally known as the "father" //commemt: Bamus being the "son") is a symmetrical large stratovolcano on New Britain Island. It rises majestically above the north coast of New Britain across a low saddle NE of Bamus volcano, the South Son. Ulawun is one Papua New Guinea's most active and most dangerous volcanoes. Rising to 2334 m, it is also the highest of the 1000 km long chain of the Bismarck volcanic arc which stretches from Rabaul volcano in the East to Wewak in the west and contains no less than 21 active volcanoes. Eruptions from Ulawun Historical records from Ulawun reach relatively far back. The historic account of an eruption of Ulawun volcano was by the English discoverer William Dampier (1651-1715) in 1700. However, lack of activity or further reports by explorers led to a large gap of informatio until, 178 years later, the Australian businessman Wilfred Powell reported activity in 1878. The largest eruptions in historic times were in 1915, 1970, and 1980. The eruption in 1915 deposited 10 cm of ash in Toriu, 50 km northeast of the volcano. The eruption of 1970 produced nuees ardentes (pyroclastic flows) and lava flows. A major eruption in 1980 produced an eruption column rising to 60,000 ft (ca. 20 km) and produced pyroclastic flows which swept all flanks of the volcano and devastated an area of 20 square km. The last larger eruptions devastated the flanks of Ulawun, produced large andesitic lava flows and greatly modified the summit crater. Typical smaller eruptions from Ulawun range from strombolian-type explosions to lava dome growth with associated small ash explosions and small nuées ardentes. -> See whole entry

Ulla Lohmann (People)

Ulla Lohmann is an internationally renowned photojournalist, adventurer and documentary filmmaker. She has travelled extensively in the South Pacific, in particular Papua New Guinea and Vanuatu, which have almost become her seond home. Exclusively for VolcanoDiscovery, Ulla organizes and guides our new expedition to Vanuatu's volcanoes. -> See whole entry

Umboi (Volcano)

Unboi Island is the largest of the volcanic Islands off the north coast of New Guinea. It is 50 km long and contains Umboi volcano, a mainly basaltic-andesitic complex of several overlapping stratovolcanoes. The Umboi volcanic complex is cut by a large 13 x 17 km caldera with up to 1 km high walls. The caldera is open to the NE and has 3 young cones containing summit crater lakes: Talo, Soal and Barik. Talo is the largest of these cones and has several thermal areas with hot springs, bubbling mud ponds and fumaroles. Talo also has flank cones. There are no known eruptions in historic times, but it is believed that the post-caldera cones habve been active within the past few hundred years. (source: Smithsonian / GVP) Umboi Island played an important role in providing wood for building sailing canoes used in ancient trade of goods including obsidian.

Una Una (Volcano)

Una Una (also known as Colo) is an isolated volcano in the Gulf of Tomni, offshore central Sulawesi. It is the site of sulfur extraction. -> See whole entry

Ungaran (Volcano)

Ungaran volcano is a probably extinct volcano south of Semarang city at the N coast of Java. Highly eroded, the mountain is the remnant of a stratovolcano that underwent repeated flank collapse. At present, there are only fumaroles and warm springs located on the volcano's flanks as signs of activity. -> See whole entry

Unnamed (Volcano)

The existence of this volcano is questionable and there are no convincing data available to confirm the existence of this volcano in the Celebes Sea. -> See whole entry

unnamed (Volcano)

A submarine eruption in 1924 was reported from a location east of Matua Island in the central Kuriles. There is a submarine volcano reaching near the surface of the sea in this location.

unnamed (Volcano)

An unnamed isolated basaltic-andesite cinder cone is located between the Corrida de Cori range on the Chile/Argentina border and the Salar Río Grande in Argentina. The cone sits on top of Miocene ignimbrites and lava flows. It has erupted relatively fluid blocky lava flows that form a broad lobe to the SE and a narrow tongue to the east nearly to the Salar Río Grande. A second smaller vent lies about 800 m NW of the cinder cone. The age of the lava flows with surficial breadcrust textures could be Holocene. (Smithsonian / GVP volcano information)

unnamed (Volcano)

An unnamed seamount is located 30 km NNE of Cape Gloucester on the NW tip of New Britain. It is probably an active submarine volcano and the most likely source of an unconfirmed submarine eruption report during 1983. An earthquake swarm accompanied the event. Local inhabitants heard sounds and saw a glow in the sea, although no firm evidence exists that a submarine eruption took place. (Smithsonian / GVP volcano information)

unnamed (Volcano)

There are 2 uncertain reports of submarine eruptions off Cape Hollman NW of Lolobau Island and east of Garove Island during 1951 and 1970, but cannot be definitively attributed to volcanic origin.

unnamed (Volcano)

A submarine volcano could exist NE of Karkar Island in the Bismarck Sea. 2 reports of submarine disturbances from 1944 and 1951 are the only evidence for a submarine volcano Island. The average sea floor depth in this area is 2000 m.

unnamed (Volcano)

A possible submarine volcano is located on the Ogasawara Plateau (3200 m depth) about 330 km NEN of Kita-Iwo-jima. A table of possible submarine eruptions by the Japanese Maritime Safety Agency included an entry of observed water discoloration due to submarine eruptions in this area in March 1974.

unnamed (Volcano)

A young volcanic field with no particular name is located in NW Tibet. The field contains a cone in the Kekexili caldera, which was previously thought to have been in eruption based on a satellite photo in 1973. This is now considered not to represent an eruption. There are several volcanoes that have erupted large fluuid lava flows in the area, similar to Hawaiian volcanoes. -> See whole entry

unnamed (Volcano)

An unnamed volcanic field is located between Taftan and Bazman citied in SE Iran. It contains very young-looking basaltic lava flows erupted from perfectly preserved cones, located in an area of eroded Cretaceous limestone peaks.

unnamed (Volcano)

An unnamed group of 5 andesitic-to-dacitic cinder cones and associated lava flows is located in northern Georgia 20 km from the Russian border and 35 km NE of the town of Tskhinvali.

unnamed (Volcano)

An unnamed group of 7 young volcanic cones is located in the Obul-Samarask upland of southern Georgia, SW of the capital city of Tbilisi, near the borders with Turkey and Armenia. The cones are early Pleistocene to Holocene in age and many of the craters have a well-preserved morphology.

unnamed (Volcano)

An unnamed submarine volcano is located 7 km NW of Kavachi volcano and might belong to the same magmatic system, i.e. represent a second vent of the same volcano. In 1992 thermal plumes were detected from one of its 2 summit craters. -> See whole entry

unnamed (Volcano)

A possible submarine eruption occurred on or before 20 July 1953 off the western coast of Baja California from an unknown submarine volcano. The report came from sailors on fishing boats who observed great numbers of dead fish and mud bubbling up at sea 2 km from San Cristóbal Island. The captain of the Scripps Institution of Oceanography vessel "Horizon" reported similar phenomena at another point near the island of Cedros, not far from San Cristóbal Bay. The origin of these events is uncertain.

unnamed submarine (Volcano)

A submarine volcano is located 30 km SE of Chirpoi Island in the central Kuriles, Russia. Hydrophones recorded an eruption in 1972 somewhere between Simushir and Urup Island. There are 3 seamounts in this area, one of which probably erupted to produce the signals.

unnamed submarine (Volcano)

A submarine volcano is located 118 km SE of Manus Island in the Bismarck Sea. The volcano was detected through acoustic signals probably produced by a submarine eruption in January 1972. The signals were similar to those from known submarine eruptions and recorded at seismic stations on nearby Mauns Island and at hydrophones on Wake and Midway Islands in the Central Pacific. -> See whole entry

Unzen (Volcano)

Unzen Volcano (雲仙岳 in Japanese), located on the Island of Kyushu about 40 kilometers east of Nagasaki city, is one of Japan's most active and dangerous volcanoes. -> See whole entry

Urataman (Volcano)

Urataman is the northernmost of the 6 volcanoes on Simushir Island, Kuriles. It has an impressive 7.5-km-wide caldera which forms the NE tip of the island. Its caldera walls rise 450 m above a 250-m-deep bay. Sea water enters the caldera through a narrow gap in the northern rim and creates the half-moon-shaped Brouton Bay, corresponding to about half the surface of the caldera. Within the past 10,000 years and after the formation of the caldera, a large new central cone, the andesitic Urataman volcano proper, has grown in the SE part of the caldera. Besides the central vent, there are 2 cinder cones on the northern and a lava dome on the NW flank of Urataman volcano.

Ushishur (Volcano)

Ushishur volcano in the central Kuriles has one of the world's most beautiful calderas, forming a almost complete ring rising above the sea. Most of the volcano's edifice is under water, but the submerged part forms 2 small islands. The southern island contains the summit caldera and the northern a portion of the volcano's flanks. The small 1.6-km-wide caldera of the southern island formed about 9400 years ago and has only a narrow breached on the south, allowing sea water to fill the caldera. Eruptions after the formation of the caldera formed small islands in the caldera bay. -> See whole entry

Usu (Volcano)

Mt Usu (有珠山) volcano is Hokkaido is one of Japan's most well-known volcanoes. The summit of Usu consists of several lava domes that formed in historic time. The last eruption was in March 2000 - September 2001, when Usu erupted for the first time in 22 years and forced the evacuation of 13,000 residents. -> See whole entry

Usulutan (Volcano)

Usulután volcano is a stratovolcano in east-central El Salvador, at the SE end of a cluster of basaltic to basaltic-andesite stratovolcanoes between San Vicente and San Miguel volcanoes. The volcano contains a broad 1.3-km-wide summit crater breached to the east. The flanks of the forested Usulután volcano are strongly eroded and suggest a long repose interval, but young lava flows are present on its southern flanks. They are probably less than 10,000 years old. Cerro Nanzal is a flank cone on the lower SE flank and was mapped as Holocene.

Utila (Volcano)

Utila volcano is a volcanic vent that has produced a small lava flow and pyroclastic cones on the small island of Utila in the Carribean Sea off the north coast of Honduras. -> See whole entry

Uturuncu (Volcano)

Uturuncu volcano is the highest peak in SW Bolivia and located SE of Quetana. The stratovolcano consists dominantly of andesitic to dacitic lava flows and some are probably less than 10,000 years old. At present, there are 2 solfatara fields near the summit. Large-scale ground deformation, a bulge growing one inch per year, has been detected since May 1992 as well as increased seismic activity. This indicates that magma is still moving beneath the volcano.


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