The list below provides definitions for commonly used geologic hazard terminology. Unless otherwise noted by a citation or brackets, the definitions below were extracted with permission from the American Geological Institute, Glossary of Geology, 5th edition, Neuendorf, Mehl, and Jackson.
A-E :: F-J :: K-O :: P-S :: T-Z
A-E
- Active fault
- A fault on which slip has occurred recently and is likely to occur in the future. [In terms of active faulting, "recently" is often defined as within the past 10,000, 13,000, or 1.6 million years before present depending on the source cited.]
- Avalanche
- A large mass of snow, ice, soil, or rock or mixtures of these materials, falling, sliding, or flowing very rapidly under the force of gravity. Velocities may sometimes exceed 500 km/hr.
- Carbon 14
- A radioactive isotope of carbon discovered February 27, 1940, by Martin Kamen and Sam Ruben. Its nucleus contains 6 protons and 8 neutrons. Its presence in organic materials is used extensively as basis of the radiocarbon dating method to date archaeological, geological, and hydrogeological samples.
- Debris flow
- A moving mass of rock fragments, soil, and mud, more than half of the particles being larger than sand size. Slow debris flows may move less than 1 m per year; rapid ones reach 160 km per hour.
- Earthquake
- A sudden motion or trembling in the Earth caused by the abrupt release of slowly accumulated strain. syn: shock, quake, seism, macroseism, temblor
- Epicenter
- The point on the Earth’s surface located directly above the focus of an earthquake.
- Erosion
- The general process or the group of processes whereby the materials of the Earth's crust are loosened, dissolved, or worn away, and simultaneously moved from one place to another, by natural agencies, which include weathering, solution, corrosion, and transportation, but usually exclude mass wasting; specifically the mechanical destruction of the land and the removal of material (such as soil) by running water (including rainfall), waves and currents, moving ice, or wind...
F-J
- Flood
- A rising body of water (as in a stream, lake, or sea, or behind a dam) that overtops its natural or artificial confines and that covers land not normally under water; esp. any relatively high stream flow that overflows its banks in any reach of the stream, or that is measured by gage height or discharge quantity.
- Gas and fluid venting forming seafloor pockmarks
- Pockmarks are shallow seabed depressions, caused by escaping gasses or fluids in areas of softer soils. Pockmarks are no longer active for the most part, however there are still some that are actively venting and depressing further.
- Geohazard
- A geological state, which represents or has the potential to develop further into a situation leading to damage or uncontrolled risk. Geohazards are found in all parts of the earth and are always related to geological conditions and geological processes, either recent or past.
- Ice push
- The lateral pressure exerted by the expansion of shoreward-moving ice, especially of lake ice. syn: ice shove; ice thrust.
- Icing
- A surface ice mass formed during the winter in a permafrost area by successive freezing of sheets of water that may seep from the ground, or from a spring or river. syn: aufeis, flood icing; river icing; flooding ice; floodplain icing.
K-O
- Landslide
- A general term covering a wide variety of mass-movement landforms and processes involving the down slope transport, under gravitational influence, of soil and rock material en masse. Usually the displaced material moves over a relatively confined zone or surface of shear. The wide range of sites and structures and material properties affecting resistance to shear, result in a great range of landslide morphology, rates, patterns of movement, and scale. Landsliding is usually preceded, accompanied, and followed by perceptible creep along the surface of sliding and/or within the slide mass. Terminology designating landslide types generally refers to the landform as well as the process responsible for it, e.g. rockfall, translational slide, block glide, avalanche, mudflow, liquefaction slide, and slump.
- Lateral spread
- Lateral movements in a fractured mass of rock or soil, which result from liquefaction or plastic flow or subjacent materials.
- Liquefaction [soil]
- In saturated, cohesionless soil, the transformation from a solid to a liquid state as a result of increased pore pressure and reduced effective stress [in response to severe ground shaking resulting from an earthquake].
- Modeling
- The creation of mathematical relationships, by an individual, to represent the happenings of a real world phenomenon. Models are generated by using what is known about an event, using field data, and using that information to create a computer simulation of the event. Scientists of all kinds build and use models not only to help explain what has happened in an event, but also to attempt to predict those that have not occurred yet in areas where conditions are similar enough to apply the model.
- Mud diapirism and mud volcanism
- Buried sediments of a mixture of low density mud and gas may flow upwards through fault lines causing venting or mud volcanoes at the seafloor surface. Gasses from the sediments can ignite or explode causing major damage to surrounding geologic and man made structures.
P-S
- Permafrost
- Any soil, subsoil, or other surfacial deposit, or even bedrock, occurring in the arctic, sub-arctic, and alpine regions at variable depth beneath the Earth's surface in which a temperature below freezing has existed continuously for a long time (from two years to tens of thousands of years). This definition is based exclusively on temperature, and disregards the texture, degree of compaction, water content, and lithologic character of the material. The thickness of permafrost ranges from over 1000 m in the north to 30 cm in the south; it underlies about one fifth of the world's land area. syn: pergelisol, perennially frozen ground.
- Pore Pressure
- The build up of pressures between particles of soil, associated with the presence/absence of water.
- Radon-220
- A radioactive, gaseous isotope of radon; it is a member of the thorium series and a daughter of radium-224.
- Rockfall
- The relatively free falling or precipitous movement of a newly detached segment of bedrock (usually massive, homogeneous, or jointed) of any size from a cliff or other very steep slope; it is the fastest form of mass movement and is most frequent in mountains during spring when there is repeated freezing and thawing of water in cracks in the rock. syn: sturzstrom .
- Salt-water encroachment
- Displacement of fresh water or ground water by the advance of salt water due to its greater density, usually in coastal and estuarine areas but also by movement of brine from beneath a playa lake toward wells discharging fresh water. Encroachment occurs when the total head of the salt water exceeds that of adjacent fresh water. syn: sea-water intrusion, intrusion, sea-water encroachment.
- Sea level rise
- Long-term increases in mean sea level. The expression is popularly applied to anticipated eustatic sea level changes due to the greenhouse effect and associated global warming. (Online American Meteorological Society glossary)
- Sedimentation
- The process of deposition of sediment.
- Seiche
- A free or standing-wave oscillation of the surface of water in an enclosed or semi-enclosed basin (as a lake, bay, or harbor) that varies in a period, depending on the physical dimensions of the basin, from a few minutes to several hours, and in height from several centimeters to a few meters; that is initiated chiefly by local changes in atmospheric pressure, aided by winds, tidal currents, and small earthquakes; and that continues, pendulum fashion, for a time after cessation of the originating force.
- Seismisity
- Seismic activity or earthquakes occur when tectonic plates rub up against each other. These earthquakes may cause underwater landslides, create tsunami, and change soil conditions (e.g. pore pressures).
- Seismic gap
- A segment of an active fault zone that has not experienced a major earthquake during a time interval within most other segments of the zone have. Seismologists commonly consider seismic gaps to have high future-earthquake potential.
- Shallow Gas
- large pockets of gas trapped under sub-marine soils. If a pocket of gas is contacted by drilling, blowouts can occur; this is a primary concern at depths from the seafloor to 3000 feet below. This is a major concern for oil drilling.
- Shallow Water Flow
- Deposits of sub-terrainian water under very low over-pressurization can flow into drilling instruments. This is a major concern for oil drilling.
- Shear Strength (of soils)
- The capacity for a soil to keep its structural integrity in tact under the influence of applied loading and confining stresses. In fine grained soils the applied stresses are transmitted to the shear bonds between the soil particles the strength of these bonds is known as the shear strength of the soil. If the applied load is too great the bonds will break and the soil will fail, land slides may occur when dealing with large soil deposits.
- Slope instability
- Considered the most serious offshore threat on both local and regional scalesSlope: The inclined surface of any part of the Earth's surface (from 2005 Glossary of Geology). Instability: Lack of physical stability; unsteadiness (The American Heritage College Dictionary 4th Edition. 2004). Weaknesses in a soil on slopes can cause landslides or avalanches, these weaknesses may be in the composition of the soil or in the case of earthquakes, rain, fire, melting permafrost, or rapid deglaciation. Large landslides and avalanches can also cause tsunamis if they fall into, or occur under water.
- Storm surge
- An abnormal, sudden rise of sea level along an open coast during a storm, caused primarily by strong winds offshore, or less frequently by a drop in atmospheric pressure, resulting in water piled up against the coast. It is most severe when accompanied by high tide. syn: surge [waves], hurricane surge, storm wave.
- Subsidence
- The sudden sinking or gradual downward settling of the Earth's surface with little or no horizontal motion. The movement is not restricted in rate, magnitude or area involved. Subsidence may be caused by natural geologic processes, such as solution, thawing, compaction, slow crustal warping, or withdrawal of fluid lava from beneath a solid crust; or by man's activity, such as subsurface mining or the pumping of oil or ground water. syn: sinkingsyn: sinking.
T-Z
- Thermokarst
- Kars like topographic features produced in a permafrost region by the local melting of ground ice and the subsequent settling of the ground. syn: cryokarst.
- Tsunami
- A gravitational sea wave produced by any large-scale, short-duration disturbance of the ocean floor, principally by a shallow submarine earthquake, but also by submarine slumps, subsidence, or volcanic eruption. It is characterized by great speed of propagation (up to 950 km/hr), and long wave length (up to 200 km), long period (varying from 5 min to a few hours, generally 10-60 min), and low observable amplitude on the open sea, although it may pile up to heights of 30 m or more and cause much damage on entering shallow water along an exposed coast (often thousands of kilometers from the source). syn: seismic sea wave, seismic surge, earthquake sea wave; tsunami.
- Volcanic
- Pertaining to the activities, structures, or rock types of a volcano.
