A geologic hazard or geohazard is an adverse geologic condition capable of causing widespread damage or loss of property and life. These

hazards A hazard is a potential source of harm. Substances, events, or circumstances can constitute hazards when their nature would allow them, even just theoretically, to cause damage to health, life, property, or any other interest of value. The probabi ...

are geological and environmental conditions and involve long-term or short-term geological processes. Geohazards can be relatively small features, but they can also attain huge dimensions (e.g., submarine or surface landslide) and affect local and regional socio-economics to a large extent (e.g.,

tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater exp ...

s). Sometimes the hazard is instigated by the careless location of developments or construction in which the conditions were not taken into account. Human activities, such as drilling through overpressured zones, could result in significant risk, and as such mitigation and prevention are paramount, through improved understanding of geohazards, their preconditions, causes and implications. In other cases, particularly in montane regions, natural processes can cause catalytic events of a complex nature, such as an avalanche hitting a lake and causing a debris flow, with consequences potentially hundreds of miles away, or creating a lahar by volcanism. Marine geohazards in particular constitute a fast-growing sector of research as they involve seismic, tectonic, volcanic processes now occurring at higher frequency, and often resulting in coastal sub-marine avalanches or devastating tsunamis in some of the most densely populated areas of the world Such impacts on vulnerable coastal populations, coastal infrastructures, offshore exploration platforms, obviously call for a higher level of preparedness and mitigation.

Speed of development

Sudden phenomena

Sudden phenomena include: *

avalanche An avalanche is a rapid flow of snow down a slope, such as a hill or mountain. Avalanches can be set off spontaneously, by such factors as increased precipitation or snowpack weakening, or by external means such as humans, animals, and eart ...

s (snow or rock) and its runout *

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 and earthquake-triggered phenomena such as

s * forest fires (espec. in Mediterranean areas) leading to

deforestation Deforestation or forest clearance is the removal of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. The most concentrated ...

geomagnetic storms A geomagnetic storm, also known as a magnetic storm, is a temporary disturbance of the Earth's magnetosphere caused by a solar wind shock wave and/or cloud of magnetic field that interacts with the Earth's magnetic field. The disturbance that d ...

gulls Gulls, or colloquially seagulls, are seabirds of the family Laridae in the suborder Lari (bird), Lari. They are most closely related to the terns and Skimmer (bird), skimmers and only distantly related to auks, and even more distantly to waders ...

(chasms) associated with cambering of valley sides *

ice jam Ice jams occur when a topographic feature of the river causes floating river ice to accumulate and impede further progress downstream with the river current. Ice jams can significantly reduce the flow of a river and cause upstream flooding—som ...

s (Eisstoß) on rivers or

glacial lake outburst flood A glacial lake outburst flood (GLOF) is a type of outburst flood caused by the failure of a dam containing a glacial lake. An event similar to a GLOF, where a body of water contained by a glacier melts or overflows the glacier, is called a j� ...

s below a

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 ...

* landslide (displacement of earth materials on a slope or hillside) *

mudflow A mudflow or mud flow is a form of mass wasting involving fast-moving flow of debris that has become liquified by the addition of water. Such flows can move at speeds ranging from 3 meters/minute to 5 meters/second. Mudflows contain a significa ...

s (avalanche-like muddy flow of soft/wet soil and sediment materials, narrow landslides) *

pyroclastic flows A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of b ...

* rockfalls,

rock slide A rockslide is a type of landslide caused by rock failure in which part of the bedding plane of failure passes through compacted rock and material collapses ''en masse'' and not in individual blocks. Note that a rockslide is similar to an avalanc ...

s, (

rock avalanche A rockslide is a type of landslide caused by rock failure in which part of the bedding plane of failure passes through compacted rock and material collapses ''en masse'' and not in individual blocks. Note that a rockslide is similar to an avalan ...

) and

debris flow Debris flows are geological phenomena in which water-laden masses of soil and fragmented rock rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors. They generally ...

s * torrents ( flash floods, rapid floods or heavy current creeks with irregular course) * liquefaction (settlement of the ground in areas underlain by loose saturated sand/silt during an earthquake event) *

volcanic eruptions Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often ...

, lahars and

ash fall Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to refer ...

Slow phenomena

Gradual or slow phenomena include: *

alluvial fan An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to semiarid climates, but a ...

s (e.g. at the exit of canyons or

side valley Side valleys and tributary valleys are valleys whose brooks or rivers flow into greater ones. Upstream, the valleys can be classified in an increasing order which is equivalent to the usual orographic order: the tributaries are ordered from tho ...

s) *

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 ...

development (volcanoes) * geyser deposits * ground settlement due to consolidation of compressible soils or due to collapseable soils (''see also compaction) * ground subsidence, sags and

sinkhole 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 ...

s * sand dune migration * shoreline and stream

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is dis ...

thermal spring A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by circ ...

Evaluation and mitigation

Geologic hazards are typically evaluated by engineering geologists who are educated and trained in interpretation of landforms and earth process, earth-structure interaction, and in geologic hazard mitigation. The engineering geologist provides recommendations and designs to mitigate for geologic hazards. Trained hazard mitigation planners also assist local communities to identify strategies for mitigating the effects of such hazards and developing plans to implement these measures. Mitigation can include a variety of measures: * Geologic hazards may be avoided by relocation. Publicly available databases, via searchable platforms, can help people evaluate hazards in locations of interest. * The stability of sloping earth can be improved by the construction of

retaining wall Retaining walls are relatively rigid walls used for supporting soil laterally so that it can be retained at different levels on the two sides. Retaining walls are structures designed to restrain soil to a slope that it would not naturally keep to ...

s, which may use techniques such as

slurry wall A slurry wall is a civil engineering technique used to build reinforced concrete walls in areas of soft earth close to open water, or with a high groundwater table. This technique is typically used to build diaphragm (water-blocking) walls surro ...

shear pin {{unreferenced, date=September 2018 A shear pin is a mechanical detail designed to allow a specific outcome to occur once a predetermined force is applied. It can either function as a safeguard designed to break to protect other parts, or as a con ...

s, tiebacks, soil nails or soil anchors. Larger projects may use

gabion A gabion (from Italian ''gabbione'' meaning "big cage"; from Italian ''gabbia'' and Latin ''cavea'' meaning "cage") is a cage, cylinder or box filled with rocks, concrete, or sometimes sand and soil for use in civil engineering, road buildin ...

s and other forms of earth buttress. * Shorelines and streams are protected against scour and erosion using revetments and

riprap Riprap (in North American English), also known as rip rap, rip-rap, shot rock, rock armour (in British English) or rubble, is human-placed rock or other material used to protect shoreline structures against scour and water, wave, or ice erosion. ...

. * The

soil Soil, also commonly referred to as earth or dirt Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty. Common types of dirt include: * Debri ...

or rock itself may be improved by means such as dynamic compaction, injection of grout or concrete, and

mechanically stabilized earth Mechanically stabilized earth (MSE or reinforced soil) is soil constructed with artificial reinforcing. It can be used for retaining walls, bridge abutments, seawalls, and dikes. Although the basic principles of MSE have been used throughout ...

. * Additional mitigation methods include

deep foundation A deep foundation is a type of foundation that transfers building loads to the earth farther down from the surface than a shallow foundation does to a subsurface layer or a range of depths. A pile or piling is a vertical structural eleme ...

tunnel A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube cons ...

s, surface and subdrain systems, and other measures. *Planning measures include regulations prohibiting development near hazard-prone areas and adoption of

building codes A building code (also building control or building regulations) is a set of rules that specify the standards for constructed objects such as buildings and non-building structures. Buildings must conform to the code to obtain planning permiss ...

In paleohistory

Eleven distinct

flood basalt A flood basalt (or plateau basalt) is the result of a giant volcanic eruption or series of eruptions that covers large stretches of land or the ocean floor with basalt lava. Many flood basalts have been attributed to the onset of a hotspot reac ...

episodes occurred in the past 250 million years, resulting in large volcanic provinces, creating

lava plateau A volcanic plateau is a plateau produced by volcanism, volcanic activity. There are two main types: lava plateaus and pyroclastic plateaus. Lava plateau Lava plateaus are formed by highly fluid basaltic lava during numerous successive erup ...

s and

mountain range A mountain range or hill range is a series of mountains or hills arranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment that have arise ...

s on Earth. Large igneous provinces have been connected to five

mass extinction An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. I ...

events. The timing of six out of eleven known provinces coincide with periods of

global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...

and marine anoxia/dysoxia. Thus, suggesting that volcanic CO₂ emissions can force an important effect on the

climate system Earth's climate system is a complex system having five interacting components: the atmosphere (air), the hydrosphere (water), the cryosphere (ice and permafrost), the lithosphere (earth's upper rocky layer) and the biosphere (living things). '' ...

Known hazards

* 2004 Indian Ocean earthquake and tsunami * 2008 Sichuan earthquake *

2011 Tōhoku earthquake and tsunami The occurred at 14:46 JST (05:46 UTC) on 11 March. The magnitude 9.0–9.1 (M) undersea megathrust earthquake had an epicenter in the Pacific Ocean, east of the Oshika Peninsula of the Tōhoku region, and lasted approximately six mi ...

The Barrier The Barrier is a lava dam retaining the Garibaldi Lake system in southwestern British Columbia, Canada. It is over thick and about long where it impounds the lake. The area below and adjacent to The Barrier is considered hazardous due to the u ...

(located in

Garibaldi Provincial Park Garibaldi Provincial Park, also called Garibaldi Park, is a wilderness park located on the coastal mainland of British Columbia, Canada, 70 kilometres (43.5 mi) north of Vancouver. It was established in 1920 and named a Class A Provincial ...

) *

Usoi Dam The Usoi Dam is a natural landslide dam along the Murghab River in Tajikistan. At high, it is the tallest dam in the world, either natural or man-made. The dam was created on February 18, 1911, when the 7.4- Ms Sarez earthquake caused a massive ...

a natural landslide dam Image:Frozen_Danube_Reichsbrücke.JPG, Eisstoß Feb.2006 Vienna, Austria (

Donauinsel The Donauinsel (Danube Island) is a long, narrow artificial island in central Vienna, Austria, lying between the Danube river and the parallel excavated channel '' Neue Donau'' ("New Danube"). The island is in length, but is only wide. The ...

) Image:Glacier.swiss.500pix.jpg, Glacier just above

Grindelwald , neighboring_municipalities = Brienz, Brienzwiler, Fieschertal (VS), Guttannen, Innertkirchen, Iseltwald, Lauterbrunnen, Lütschental, Meiringen, Schattenhalb , twintowns = Azumi, now Matsumoto (Japan) Grindelwald is a village and ...

, Switzerland Image:Liquefaction at Niigata.JPG, Soil liquefaction during the

1964 Niigata earthquake Events January * January 1 – The Federation of Rhodesia and Nyasaland is dissolved. * January 5 - In the first meeting between leaders of the Roman Catholic and Orthodox churches since the fifteenth century, Pope Paul VI and Patriarc ...

References

External links

*
International Centre for Geohazards (ICG)
{{DEFAULTSORT:Geologic hazards Physical geography Geomorphology Disasters