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Huge landslide at La Conchita, 1995

A geologic hazard is one of several types of adverse geologic conditions capable of causing damage or loss of property and life. These hazards can consist of sudden or slow phenomena:

• avalanches (snow, rock, or air & snow) and its runout
• earthquakes and earthquake-triggered phenomena
• fault rupture (displacement of the terrain or ground along a geological fault), recent (active) fault (exhibiting actual movement or seismic activity)
• forest fires (espec. in mediterranean areas)
• ice jams or ice impact (Eisstoß) on rivers or below a glacier
• landslide (lateral displacement of earth materials on a slope or hillside)
• mudflows (avalanche-like muddy flow of soft/wet soil and sediment materials, narrow landslides)
• pyroclastic flows
• rock falls, rock slides, (rock avalanche) and debris flows
• torrents (flash floods, rapid floods or heavy current creeks with irregular course)
• volcanic eruptions, lahars and ash falls.

Rather gradual or slow phenomena are e.g.:

• alluvial cones (e.g. at the exit of canyons or side valleys)
• caldera development (volcanoes)

Norris geyser at Yellowstone NP, Sept.2003

• geyser deposits
• ground settlement due to consolidation of compressible soils or due to collapseable soils (see also compaction)
• ground subsidence, sags and sinkholes
• liquefaction (settlement of the ground in areas underlain by loose saturated sand/silt during an earthquake event)
• sand dune migration
• shoreline and wave erosion
• thermal springs

Sometime the hazard is instigated by man through the careless location of developments or construction in which the conditions were not taken into account.

Geologic hazards are evaluated by an engineering geologist educated, trained and experienced in engineering geology for their, investigation and analysis, often in conjunction with a geotechnical engineer. The engineering geologist is qualified to formulate recommendations for the mitigation of the hazards. Mitigation can include avoidance of the hazards or relocation; construction of slope stabilization measures (earth buttress, retaining walls, diversion walls, shear pins, tiebacks, soil nails or soil anchors, revetments, injection of grout or concrete, deep foundations, tunnels, subdrains), and other measures.

Eisstoß Feb.2006 Vienna, Austria (Donauinsel)

Glacier just above Grindelwald, Switzerland