A fissure is a long, narrow crack opening along the surface of Earth. The term is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in Earth's crust, on and , and on .
Ground fissure
[[File:Fissure in the ground – Almannagjá.jpg|thumb|240px|
A fissure in the lava field of
Þingvellir National Park, Iceland]]
A , also called an , is a long, narrow crack or linear opening in the Earth's crust. Ground fissures can form naturally, such as from
and
, or as a consequence of human activity, such as oil mining and groundwater pumping.
Once formed, ground fissures can be extended and eroded by
torrential rain.
They can be hazardous to people and livestock living on the affected surfaces and damaging to property and
infrastructure, such as roads, underground pipes, canals, and dams.
In circumstances where there is the extensive withdrawal of groundwater, the earth above the water table can subsidence causing fissures to form at the surface.
Crevasse
A , also called an , is a deep linear crack in an
ice sheet or
glacier resulting from the opposing force produced by their movement at different rates of speed. The force builds until their associated
shear stress is sufficient to break the ice along the faces. The breakage often forms vertical or near-vertical walls, which can melt and create
,
, and other ice formations.
A crevasse may be as deep as and as wide as .
A crevasse may be covered, but not necessarily filled, by a
snow bridge made of the previous years' accumulation and snow drifts. The result is that crevasses are rendered invisible, and extremely dangerous to anyone attempting to traverse a glacier.
Types of crevasses
-
Longitudinal crevasses form parallel to the ice flow where the glacier width is expanding.
-
Splaying crevasses appear along the edges of a glacier.
-
Transverse crevasses form in a zone of longitudinal extension where the principal stresses are parallel to the direction of glacier flow.
Fissure vent
A , also known as a or , is a long
volcanic vent through which lava erupts. Fissure vents are connected to deep
and are typically found in and along
and
.
They are commonly associated with
. Over time fissure vents form
and can feed
and
.
Karst terrain
or simply are vast regions of barren land with rocky ground and generally consisting of nearby caves, fissured ground, and [[sinkholes]]. Although these regions normally have moderate to heavy rainfall, they are noticeably devoid of vegetation and characteristically have no lakes, rivers, or streams on their surface. They form when large to massive veins of soluble aggregate like [[limestone]], [[gypsum]], or dolomite are excavated by underground torrents of flowing water.
Karst aquifers
In the United States, about 40% of the groundwater used for drinking comes from .
Some of these areas are well known vacation destinations like
Carlsbad Caverns and
Mammoth Cave. Karst aquifers are a vital resource in the US; about 20 percent of the land surface in the US is classified as karst. Other parts of the world with large areas of karst include the
Caribbean, China, and Australia.
Typical karst hydrogeology consists of a network of interconnected fissures, fractures, and conduits emplaced within permeable rock. Most of the groundwater flow occurs through a network of openings, while groundwater is held in storage within the geological structures themselves.
See also
External links
