What is a crater?

A crater is a circular crater formed on the ground by a volcanic eruption that accumulates in the surrounding area. Small, often funnel-shaped or bowl shaped, usually located at the tip of a volcano cone (cone crater is on the ground, called negative crater). The depth of the crater is not equal to that of two or three hundred meters, generally within a kilometer of diameter. The bottom diameter is short, often only about larger than the lower volcanic tube.
The crater, as the name suggests, is the exit of a volcano. It is usually at the top of the volcano, a round depression, shaped like a bowl, which means "bowl" in Greek. But it might be better to use a funnel to describe it. This "funnel" has a long tunnel connected to the underground magma, and when the volcano erupts, the magma bursts out of it.
The crater was not what it was today. Mexico Paris libraries butyl volcanic has just started, people to see the underground there is only a few centimeters wide cracks in smoke, when there is no "mountain", is a flat ground. But after three hours the cracks widened to nine metres and the eruption began to erupt. Later, the debris and the lava spewed around the crater piled up unceasingly, the pile of higher and higher, to become a cone-shaped peaks, reached the height of the hundreds of meters, and the crater is located at the top of the mountain high. But volcanoes are not always active, and the heights they can accumulate are limited. After its temporary suspension, the crater will also be damaged by rain water. If the magma in the underground condenses, the volume shrinks, making it more likely that the upper layers of rock will be fractured by the void below, and the craters will collapse around the crater and expand to a great extent.

Sometimes when a volcano in eruption again, because of the underground magma viscosity, in the energy accumulation was great in the form of explosion, then tend to put the original volcanic cone, blow up a big piece or all blow up, just leave a hole on the ground, a lot of time just on the edge of the pit or pit erupt again, form the new volcanic cone and crater. Bits to the crater of the earth also is not all caused by once again broke out, some volcanic eruption soon stop, not into conical mountain, crater appears however is the pit on the ground, which often water into a lake.