A caldera forms as a volcano's magma chamber empties, resulting in a loss of support for the earth above it. These bowl-shaped depressions can range in size from a few hundred meters to several kilometers wide. They are generally caused by large volcanic eruptions.Know More
Calderas and craters are not to be confused. Craters are created by an explosion of rock upward from a volcanic blast. Calderas are created by a sinking of the earth into the empty magma chamber left behind after the eruption.
The intense pressure of trapped gases in the magma chamber bulges the earth above and creates vents and cracks in the land. Once this pressure is released, the earth collapses back into the now empty space from which the pressure appeared. Sometimes the land collapses irregularly, leaving behind an uneven depression.
Eruptions large enough to create calderas have not occurred during recorded human history. However, geologic evidence indicates massive eruptions in Earth's past creating calderas such as the one found in Yellowstone National Park. The Yellowstone Caldera lies above a magma chamber 24 to 48 miles wide. The last eruption of this magma chamber occurred approximately 640,000 years ago and was 1,000 times larger than the eruption of Mt. Saint Helens.Learn More
Australia is the only continent without an active volcano. There are two active volcanoes off the continent of Australia but still within Australian territory. They are located on Heard Island and on the McDonald Islands.Full Answer >
According to the United States Geological Survey, before a volcanic eruption, magma must travel upwards through rock. The travelling magma produces these precursors to an eruption: an increase in earthquakes beneath a volcano, volcanic tremors, disturbance of ground features, increased release of steam from the volcano, increased temperatures and increase of gases. Additionally, different catalysts occur beneath the earth's surface prior to an eruption.Full Answer >
Volcanoes erupt to release pressure built up in the magma chamber by expelling the magma as lava. Along with lava, a volcanic eruption releases ash and greenhouse gases such as sulfur dioxide and carbon dioxide.Full Answer >
Astronomers theorize that over 4.5 billion years ago, Theia, an object about the size of Mars, collided with Earth to create a tilted axis. This is called "the giant impact theory." Prior to this event, the axis was straight at 180 degrees.Full Answer >