A volcanic crater is an approximately circular depression in the ground caused by
volcanic activity.
It is typically a bowl-shaped feature containing one or more vents. During
volcanic eruptions, molten
magma and
volcanic gases rise from an underground
magma chamber, through a conduit, until they reach the crater's vent, from where the gases escape into the atmosphere and the magma is erupted as
lava. A volcanic crater can be of large dimensions, and sometimes of great depth. During certain types of
explosive eruption
In volcanology, an explosive eruption is a volcanic eruption of the most violent type. A notable example is the 1980 eruption of Mount St. Helens. Such eruptions result when sufficient gas has dissolved under pressure within a viscous magma such ...
s, a volcano's magma chamber may empty enough for an area above it to subside, forming a type of larger depression known as a
caldera
A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...
.
Geomorphology
In most volcanoes, the crater is situated at the top of a mountain formed from the erupted volcanic deposits such as
lava flow
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or und ...
s and
tephra. Volcanoes that terminate in such a summit crater are usually of a conical form. Other volcanic craters may be found on the flanks of volcanoes, and these are commonly referred to as flank craters. Some volcanic craters may fill either fully or partially with rain and/or melted snow, forming a
crater lake.
A crater may be breached during an eruption, either by explosions or by
lava, or through later erosion. Breached craters have a much lower rim on one side.
Some volcanoes, such as
maar
A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption (an explosion which occurs when groundwater comes into contact with hot lava or magma). A maar characteristically fills with water to form a relatively shallow ...
s, consist of a crater alone, with scarcely any mountain at all. These volcanic explosion craters are formed when magma rises through water-saturated rocks, which causes a
phreatic eruption
A phreatic eruption, also called a phreatic explosion, ultravulcanian eruption or steam-blast eruption, occurs when magma heats ground water or surface water. The extreme temperature of the magma (anywhere from ) causes near-instantaneous evapo ...
. Volcanic craters from phreatic eruptions often occur on plains away from other obvious volcanoes. Not all volcanoes form craters.
See also
*
Footnotes
External links
Volcanic Features and Landforms: Cratersby US
National Park Service
{{Earth's landforms
Volcanic landforms