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Types and Processes Gallery - Craters

Craters
Craters differ from calderas both in size and origin. Craters are much smaller features than calderas and are typically defined as being less than 1 km in diameter. Although both craters and calderas are most often associated with explosive eruptions, craters are typically formed by the explosive ejection of material in and surrounding the upper part of the conduit, rather than by collapse. Steep-walled pit craters, in contrast, often found on shield volcanoes, are more passive features formed when magma drains from a fissure, leaving overlying lava flows unsupported. Multiple explosive eruptions can form overlapping or nested craters, and adjacent craters may reflect localized areas of eruption along fissures, as seen in craters rows in Iceland that extend for tens of kilometers. Maars and tuff rings are broad, low-rimmed craters formed during powerful explosive eruptions involving magma-water interaction. The accumulation of material ejected from craters contributes to the formation of their surrounding rims.

West Eifel Volcanic Field
The Mehrener maar is one of about 80 maars of the West Eifel Volcanic Field. The village of Mehrener is located on the shore of a lake partially filling the crater, whose rim lies behind the village. Maars, scoria cones, and small stratovolcanoes cover an area of 600 km2, W of the Rhine River. Most of the volcanic features formed during eruptions between about 730,000 and 10,000 years ago.

Photo by Richard Waitt, 1990 (U.S. Geological Survey).


Ol Doinyo Lengai
The northern crater of Ol Doinyo Lengai is seen here in February 1980 from the summit. The steep-walled inner crater formed during the explosive eruptions of 1966 and 1967. Another eruption began three years after this photo was taken. By December 1988 the crater filled with lava that had overflowed the near southern crater rim at the lower center of the photo.

Photo by Peterson, 1980 (courtesy of Celia Nyamweru, Kenyatta University).


Kelimutu
The two crater lakes of Kelimutu volcano on Indonesia's Flores Island are seen in this aerial view from the SW. Tiwu Nua Muri Kooh Tai (Lake of Young Men and Maidens) on the left and Tiwu Ata Polo (Bewitched or Enchanted Lake) are separated by a narrow crater wall about 35 m high. Phreatic eruptions have occurred from Tiwu Nua Muri Kooh Tai in the 19th and 20th centuries.

Photo by Tom Casadevall, 1986 (U.S. Geological Survey).


Maly Semyachik
Troitsky crater, the youngest of six craters at the summit of Kamchatka's Maly Semyachik volcano, was formed during a major explosive eruption about 400 years ago. The crater, seen here from the W with the Pacific Ocean in the background, is at the summit of Ceno-Semyachik. This is the youngest of the four overlapping stratovolcanoes that comprise the Maly Semyachik massif. The crater is now filled by a hot, acidic lake and has been the source of historical eruptions.

Photo by Dan Miller, 1990 (U.S. Geological Survey).


Douglas
A plume emitting from active fumaroles is on the N side (left center) of the summit lake at Douglas volcano on the northern tip of the Alaska Peninsula. The small, 160-m-wide crater is one of the few ice-free areas on Douglas volcano. In 1992, the lake had a pH of 1.1 and a temperature of 21°C.

Photo by Chris Nye (Alaska Division of Geological and Geophysical Surveys).


Pinacate
McDougal crater on the NW side of the Pinacate Volcanic Field in NW México is the largest maar at Pinacate. This view from the SE looks across the 1,520 x 1,740 m wide crater, which contains playa deposits 130 m below the rim. The maar erupted through flat-lying alluvial terrain of the Gran Desierto.

Photo by Richard Waitt, 1988 (U.S. Geological Survey).


Chichinautzin
Xico is a low circular tuff ring within Mexico City that is part of the Chichinautzin volcanic field, seen here from the S. This volcano was formed by phreatomagmatic eruptions through the middle of Lake Chalco, the remains of which can be seen surrounding the tuff ring. Chalco and Lakes Texcoco and Xochimilco were formed when lava flows blocked river drainages to the S.

Photo by Hugo Delgado, 1994 (Universidad Nacional Autónoma de México).


Telica
This photo taken on July 1987 looks into the double summit crater of Telica volcano in Nicaragua. An older shallower crater is located on the SW side (top). A plume rises from fumaroles in the 120-m-deep NE crater (bottom), which is the source of recent eruptions.

Photo by William Melson, 1987 (Smithsonian Institution).


Las Pilas
The lake-filled Laguna de Asososca maar in the foreground and the Cerro Asososca cone to the right were formed by eruptions at the southern end of a N-S fissure system of the Las Pilas volcanic complex in Nicaragua. The ages of these vents are not known. This view looks from the NE across the broad plain at the foot of the Cordillera de los Maribios to the Pacific Ocean in the distance.

Photo by Jaime Incer, 1981.


Cotopaxi
The glacier-capped summit of Ecuador's Cotopaxi volcano has two nested summit craters. The outer crater, seen here from the SE, is 550 x 800 m wide. A cone that grew inside this crater contains a smaller crater that is 250 m wide and 120 m deep. Frequent explosive eruptions during historical time have modified the shape of the summit crater. In 1903 the outer crater was 450 m deep.

Photo by Tom Simkin (Smithsonian Institution).


Erebus
The summit of Antarctica's Mount Erebus is the world's southernmost active volcano. It contains an elliptical 500 x 600 m wide crater whose NE side contains a 250-m-wide, 100-m-deep inner crater. The flat, snow-covered floor of the Main Crater is about 100 m below its rim. A plume rises from the inner crater that has contained an active lava lake since 1972.

Photo by Bill Rose, 1983 (Michigan Technological University).