Large calderas

Caldera

A caldera (Portuguese caldeira, meaning "cauldron"), is a circular depression or nearly at the top of some large volcanoes.
The caldera is usually surrounded by high cliffs hundreds of meters high. Calderas can reach sizes of tens of kilometers in diameter, like that of Lake Toba on Sumatra island (100 km × 30 km).
Large calderas fill with water over time and form of lakes like the Toba, Crater Lake in the United States or in the Rift Askja is Icelandic.

The caldera open to the sea, forming bays or gulfs as Santorini (Greece), Rabaul (Papua New Guinea) or Campi Flegrei (Italy).
Calderas form as a result of a cataclysmic explosion of the volcano, where a giant magma chamber is emptied in a few hours forming a large depression whose width depends on the size of the magma chamber.
The eruptions cause rapid evacuation of the magma chamber and collapse of the summit overlooking the volcano.

Such super-eruptions usually have global climatic impacts. The holes left by the caldera roughly resemble the craters formed by meteorite impact.

Image: The volcano Teide rises to 3718 meters altitude on the island of Tenerife, in the center of the Canaries. Teide stands at the center of the caldera called Las Cañadas, nearly 15 km from east to west in places with cliffs over 500 m high. Viewed from Panorama Roques de García.

Toba in Indonesia

Toba is located on the island of Sumatra, on the subduction zone between the Indo-Australian Plate and Eurasian.
The super volcano on the island of Toba in Indonesia is the subject of a catastrophic theory on human evolution by Stanley Ambrose, a professor at the University of Illinois at Urbana-Champaign.
Volcanoes can cause massive climate disasters, causing a sudden cooling of the Earth's mean temperature. The super volcano eruption of Indonesia on the island of Toba, there are about 73 000 years, spewed massive amounts of ash estimated at about 800 cubic kilometers falling to 3 100 km from the volcano.
By comparison, the eruption of Mount Pinatubo in the early 1990s, has issued only 10 cubic kilometers of ash. The ashes of Pinatubo have changed the albedo of the Earth and brought down its mean temperature 0.6 ° C for two years.

In 1998, Stanley Ambrose, said that the eruption of Toba caused a global cooling of the planet for 1800 years.

Image: Nestled in the heart of the rainforest of Sumatra, the caldera of the island of Toba has impressive dimensions. With its 30 km wide and 100 km long, the caldera is one of the largest in the world. The ancient caldera is filled by a lake in the middle of which lies the island of Samosir, embodying the old dome of the volcano.
credit image: NASA/GSFC/METI/Japan Space Systems, and U.S./Japan ASTER Science Team

Caldera Santorini in Greece

The volcanic island of Santorini (the Venetian name Santa Irina - St. Irene), located in the Aegean, is composed of five apparently separate islands.
The site has a circular shape, which corresponds to the central portion (caldera) of a collapsed volcano, which exploded in Minoan times.
The ancient island Kallista was partially destroyed around 1628 BC. AD The remains of this eruption, causing the disappearance of the Minoan civilization, are now islands of Santorini, and Thirasia Aspronissi. This cataclysm is the ancient origin of the Myth of Atlantis.
The perimeter of the ancient volcano gave the main island Thera (Fira delivered) to the west you can see and the island of Therasia Aspronisi.
Recent volcanic eruptions (16th and 17th century) created in the middle of the caldera, Palea Kameni and Nea Kameni (dark center of the image).
What beautiful scenery when we arrived in the white villages perched on cliffs overlooking the caldera red SANTORINI, home despite the danger, a few thousand people. Recently, in 1956, the island of Santorini was shaken by an earthquake which caused a further collapse of the crater of the hat. This catastrophe made a fifty people and destroyed over 2,000 homes.

The largest volcanic cone of Nea Kameni in the center of the archipelago is made entirely of black slag.
The volcanic explosion that took place there nearly 3,500 years, has carved the caldera, now considered a natural wonder known for its beautiful scenery, for its amazing sunsets from the town of Oia.

Image: Satellite image of the archipelago of Santorini, the island of Santorini on the right.
This incomplete ring of 8 km in diameter and 85 km2, circumscribed islands of Thera and Therasia which are remnants of the old island Kallista before the collapse created this volcanic caldera.
credit image: NASA/GSFC/METI/Japan Space Systems, and U.S./Japan ASTER Science Team

Caldera Crater Lake in Oregon

Crater Lake is a caldera more than 9 km in diameter located in the Cascade Mountains, south-western state of Oregon in the United States.
With 597 meters deep, the caldera is the deepest lake in North America.
The Cascade Range is a subduction zone where the eruptive activity is intense.
There are about 500 000 years, Mount Mazama rose to 3550 meters.
Between 5700 and 4800 BC. AD an explosive eruption pours millions of tons of ash to Wyoming, Nevada and British Columbia.
It is this explosive eruption of Mount Mazama, which disintegrated, leaving only the huge caldera whose edges have an average altitude of 2300 meters.

Rain and snow have finally fill the caldera, creating Crater Lake.
Crater Lake area remains a closely watched of the Cascade Mountains as a violent explosive eruption remains possible by volcanologists.

Image: Located at 2100 meters above sea level, Crater Lake is the deepest of the United States with a depth of 597 meters.
credit image Wikimedia Commons.

Caldera Askja in Iceland

The volcano Askja ("Caldera" in Icelandic), belongs to the zone of volcanic Dyngiufjöll. The volcano is 8 km in its longest dimension and its surface exceeds 40 square kilometers. A circular wall of 250 to 400 meters high contains the caldera. Askja the caldera is located in the central part of North-eastern highlands of Iceland.
The Askja includes several calderas, a vast lake occupies the south-east of the main caldera whose rim the south and east are particularly steep.
The circular crater with a depth of 224 meters.
Nearby lies the Viti, a small explosion crater 60 meters deep, formed during the violent eruption of 1875.
In March 1875, two explosions inside the caldera, threw 2.5 km3 of tephra in 7 months. Ash clouds veiled the north-east Iceland preventing sunlight to penetrate.

The perceived background of the caldera is relatively flat, but the lake Öskjuvatn, hide of 11 km², a second caldera of more than 200 meters deep.
This is the deepest lake in the country.

Image: The vast desert volcanic volcano Askja and cold water lake blue, along six miles. Lake Askjuvatn appeared in 1975 during a massive volcanic eruption.
credit image: United States Geological Survey, an agency of the United States Department of Interior.

Rabaul caldera volcano in Papua New Guinea

The Rabaul is a volcanic complex stratovolcanoes, cones, craters, domes and calderas located on the island of New Britain in the Bismarck Sea in continuation with the island of Papua New Guinea.
The volcano consists of a semi-caldera open to the sea and its caldera forms a natural harbor that is home to the town of Rabaul.
On both sides of the caldera are the eruptive vents of the volcano or pyroclastic cones, the Vulcan 243 meters high (on the image, it is located on the left side of the bay) and Tavurvur, top 223 meters (on the image is located right on the peninsula in front of Vulcan).
The highest cone is the stratovolcano, the Kombiu rises to 688 meters (on the image is located on the peninsula above Tavurvur). The Rabaul submarine caldera measures 14 km from north to south and 9 km from east to west, with a depth of 60 meters in the northern part and 300 meters in the southern part. North of the caldera collapse we can see Mount Tovanumbatir, 480 meters high, and on its lush southern flank lies the town of Rabaul, built inside the volcano, northeast of the caldera, which has not less than 70 000 inhabitants.

A powerful explosive eruption occurred in 1994.
Simultaneously the mouths of Vulcan and Tavurvur have erupted forcing the temporary evacuation of the town of Rabaul. The caldera occur when a massive eruption, empty magma chamber underlying of the volcano. The emptying of the room leaving a crater on the surface.
The eruptions that formed Rabaul Caldera occurred recently, there 3500 years and 1400 years.

Image: satellite image of the Rabaul caldera in Papua New Guinea, located on the island of New Britain.
credit image Wikimedia Commons.