A fissure is a long, narrow crack opening along the surface of

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

. The term is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in Earth's crust, on

ice sheet In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are in Antarctica and Greenland; during the Last Glacial Period at La ...

s and

glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such as ...

s, and on

volcano A volcano is a rupture in the Crust (geology), crust of a Planet#Planetary-mass objects, planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and volcanic gas, gases to escape from a magma chamber below the surface. On Ear ...

es.

Ground fissure

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 tectonic faulting and

earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, fr ...

s, 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 Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water fo ...

. 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 Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidated ...

, the earth above the

water table The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated. T ...

can subside causing fissures to form at the surface. This typically occurs at the floor of arid valleys having rock formations and compacted soils with a high percentage of fine-grained material.

Crevasse

A , also called an , is a deep linear crack in an

resulting from the opposing force produced by their movement at different rates of speed. The force builds until their associated

shear stress Shear stress, often denoted by (Greek: tau), is the component of stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross section. ''Normal stress'', on the ...

is sufficient to break the ice along the faces. The breakage often forms vertical or near-vertical walls, which can melt and create seracs, arches, 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 A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ...

vent through which lava erupts. Fissure vents are connected to deep magma reservoirs and are typically found in and along

rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...

s and

rift zone A rift zone is a feature of some volcanoes, especially shield volcanoes, in which a set of linear cracks (or rifts) develops in a volcanic edifice, typically forming into two or three well-defined regions along the flanks of the vent. Believed t ...

s. They are commonly associated with shield volcanoes. Over time fissure vents form

spatter cone Volcanic cones are among the simplest volcanic landforms. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and s ...

s and can feed

lava channel A lava channel is a stream of fluid lava contained within zones of static (i.e., solid and stationary) lava or lava levees. The initial channel may not contain levees per se, until the parental flow solidifies over what develops into the channel and ...

s and lava tubes.

Karst terrain

or simply are vast regions of barren land with rocky ground and generally consisting of nearby caves, fissured ground, and

sinkholes A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are locally also known as ''vrtače'' and shakeholes, and to openi ...

. 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 Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywal ...

, 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 Carlsbad Caverns National Park is an American national park in the Guadalupe Mountains of southeastern New Mexico. The primary attraction of the park is the show cave Carlsbad Cavern. Visitors to the cave can hike in on their own via the natur ...

and

Mammoth Cave Mammoth Cave National Park is an American national park in west-central Kentucky, encompassing portions of Mammoth Cave, the longest cave system known in the world. Since the 1972 unification of Mammoth Cave with the even-longer system under F ...

. 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.

List of karst aquifers in North America

Arbuckle-Simpson aquifer

Basin and Range and Bear River range carbonate aquifers

Colorado Plateau karst

Edwards Balcones Fault Zone aquifer

Edwards-Trinity Plateau aquifer

Upper Floridan and Biscayne aquifers

Madison aquifer

Midwest Paleozoic Carbonate aquifers

New England karst aquifers

Ozark Plateau karst aquifers

Roswell Basin aquifer

Pacific Northwest basalt aquifers

Valley and Ridge, Piedmont, and Blue Ridge aquifers

References

External links

External images of Almannagja fissures
{{structural geology, state=collapsed Geomorphology Patterned grounds Structural geology