
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 Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...
. The term is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in
Earth's crust
Earth's crust is its thick outer shell of rock, referring to less than one percent of the planet's radius and volume. It is the top component of the lithosphere, a solidified division of Earth's layers that includes the crust and the upper ...
, on
ice sheet
In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacier, glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice s ...
s and
glacier
A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
s, and on
volcano
A volcano is commonly defined as a vent or fissure 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 oft ...
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 earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...
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.
They can be hazardous to people and livestock living on the affected surfaces and damaging to property and
infrastructure
Infrastructure is the set of facilities and systems that serve a country, city, or other area, and encompasses the services and facilities necessary for its economy, households and firms to function. Infrastructure is composed of public and pri ...
, 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 Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available fresh water in the world is groundwater. A unit ...
, the earth above the
water table
The water table is the upper surface of the phreatic zone or zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with groundwater, which may be fresh, saline, or brackish, depending on the loc ...
can
subside causing fissures to form at the surface.
This typically occurs at the
floor
A floor is the bottom surface of a room or vehicle. Floors vary from wikt:hovel, simple dirt in a cave to many layered surfaces made with modern technology. Floors may be stone, wood, bamboo, metal or any other material that can support the ex ...
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
ice sheet
In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacier, glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice s ...
or
glacier
A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
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 alphabet, Greek: tau) is the component of stress (physics), stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross secti ...
is sufficient to break the ice along the faces. The breakage often forms vertical or near-vertical walls, which can melt and create
seracs,
arch
An arch is a curved vertical structure spanning an open space underneath it. Arches may support the load above them, or they may perform a purely decorative role. As a decorative element, the arch dates back to the 4th millennium BC, but stru ...
es, 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 commonly defined as a vent or fissure 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 fo ...
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-graben ...
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 ...
s.
They are commonly associated with
shield volcano
A shield volcano is a type of volcano named for its low profile, resembling a shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more viscous lava ...
es. Over time fissure vents form
spatter cones and can feed
lava channels 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. 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 is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...
,
gypsum
Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, 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, drywall and blackboard or sidewalk ...
, 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
Mammoth Cave National Park is a List of national parks of the United States, national park of the United States in south-central Kentucky. It encompasses portions of Mammoth Cave, the List of longest caves, longest known cave system in the worl ...
. 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
The Caribbean ( , ; ; ; ) is a region in the middle of the Americas centered around the Caribbean Sea in the Atlantic Ocean, North Atlantic Ocean, mostly overlapping with the West Indies. Bordered by North America to the north, Central America ...
, 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
*
Fabric (geology)
In geology, a rock's fabric describes the spatial and geometric configuration of all the elements that make it up. In sedimentary rocks, the fabric developed depends on the depositional environment and can provide information on current direc ...
*
Fissure vein
*
Thermokarst
Thermokarst is a type of terrain characterised by very irregular surfaces of marshy hollows and small hummocks formed when ice-rich permafrost thaws. The land surface type occurs in Arctic areas, and on a smaller scale in mountainous areas such ...
*
Topography
Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the landforms and features themselves, or a description or depiction in maps.
Topography is a field of geoscience and planetary sci ...
References
External links
External images of Almannagja fissures
{{structural geology, state=collapsed
Geomorphology
Patterned grounds
Structural geology