Natural hazard is a naturally occurring environmental disaster or human bad effecting. Basically two type of natural hazard classified. There are Geophysical and Biological hazard. Geophysical hazard is into Geological and Meteorological phenomena such as Avalanche, Earthquake, Coastal erosion, Lahar, Landslide, Sinkhole, Volcanic eruption
Geohazard is a widespread damage or risk. Geohazards 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 and affect local and regional socio-economy to a large extent
A landslide is a form of mass extinction involving a variety of earth movements such as rockfalls, deep slope failure, and shallow debris. Landslides can occur underwater called underwater landscape, coastal and onshore environment. Although it is the primary driving force for gravitational drift, there are other factors that affect the original slope stability. The actual slip usually requires a trigger before it is published, whereas typically, the pre-conditional factors are to create specific subsurface conditions prone to slope failure. The landslides should not be mixed with the mud which is a mass depletion form associated with a very rapid rash flow partially or totally liquefied by adding significant quantities of water to the starting material.
Causes of Landslides
- Destabilize of Slope reason groundwater
- There is no vertical vegetative structure, soil nutrients, and soil structure
- Erosion reasons to river or sea waves
- weakening of a slope to snow and glacier melting
- Earthquake disrupt of slope
- Volcanic eruptions.
Types of Landslides
A Debris Flow is basically a fast-moving landslide made up of liquefied, unconsolidated, and saturated mass that resembles flowing concrete. In this respect, they are not dissimilar from avalanches, where unconsolidated ice and snow cascades down the surface of a mountain, carrying trees and rocks with it.
A common misconception is to confuse debris flows with landslides or mudflows. In truth, they differ in that landslides are made up of a coherent block of material that slides over surfaces. Debris flows, by contrast, are made up of “loose” particles that move independently within the flow.
Similarly, mud flows are composed of mud and water, whereas debris flows are made up larger particles. All told, it has been estimated that at least 50% of the particles contained within a debris flow are made-up of sand-sized or larger particles (i.e. rocks, trees, etc).
Overpressured zones (including gas and shallow water flows)
Overpressured zone is oil and gas blast out of underground trap machanism to under high pressure. Usually these zones occur oil and gas drilling process
During the 1991 Gulf War, the retreating Iraqi soldiers dynamited the wellheads off more than six hundred Kuwati oil wells, creating one of the biggest man-made environmental disasters in history. Since most Kuwati wells flow without pumps under their own great pressure, the oil and gas erupted from the ground with tremendous force. It was first estimated that it would take 2 years to repair all the wells. However, the heroic and extremely dangerous job was actually done in about six months.
Mud flows, diapirism and volcanism/volcanoes
Mud flow definition is extremely rapid surging flow to become significant amount of water to the source material. Mud mostly contain clay ,so ıt makes more fluid depris lows.
Areas at risk
- Areas where wildfires or human modification of the land have destroyed vegetation
- Areas where landslides have occurred before
- Steep slopes and areas at the bottom of slopes or canyons
- Slopes that have been altered for construction of buildings and roads
- Channels along streams and rivers
- Areas where surface runoff is directed
A flood 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. Flood basalt provinces such as the Deccan Traps of India are often called traps, after the Swedish word trappa (meaning “stairs”), due to the characteristic stairstep geomorphology of many associated landscapes. Michael Rampino and Richard Stothers (1988) cited eleven distinct flood basalt episodes occurring in the past 250 million years, creating large volcanic provinces, plateaus, and mountain ranges. However, more have been recognized such as the large Ontong Java Plateau, and the Chilcotin Group, though the latter may be linked to the Columbia River Basalt Group. Large igneous provinces have been connected to five mass extinction events, and may be associated with bolide impacts.
Earthquakes and seismicity
Earthquakes are caused by the sudden release of slowly accumulated strain energy along a fault in the earth’s crust. Earthquakes and volcanoes occur most commonly at the collision zone between tectonic plates. Earthquakes represent a particularly severe threat due to the irregular time intervals between events, lack of adequate forecasting, and the hazards associated with these:
- Ground shaking is a direct hazard to any structure located near the earthquake’s center. Structural failure takes many human lives in densely populated areas.
- Faulting, or breaches of the surface material, occurs as the separation of bedrock along lines of weakness.
Landslides occur because of ground shaking in areas having relatively steep topography and poor slope stability.
Liquefaction of gently sloping unconsolidated material can be triggered by ground shaking. Flows and lateral spreads (liquefaction phenomena) are among the most destructive geologic hazards.
Subsidence or surface depressions result from the settling of loose or unconsolidated sediment. Subsidence occurs in waterlogged soils, fill, alluvium, and other materials that are prone to settle.
Tsunamis or seismic sea waves, usually generated by seismic activity under the ocean floor, cause flooding in coastal areas and can affect areas thousands of kilometers from the earthquake center.
Volcanoes are perforations in the earth’s crust through which molten rock and gases escape to the surface. Volcanic hazards stem from two classes of eruptions:
- Explosive eruptions which originate in the rapid dissolution and expansion of gas from the molten rock as it nears the earth’s surface. Explosions pose a risk by scattering rock blocks, fragments, and lava at varying distances from the source.
Effusive eruptions where material flow rather than explosions is the major hazard. Flows vary in nature (mud, ash, lava) and quantity and may originate from multiple sources. Flows are governed by gravity, surrounding topography, and material viscosity.
Hazards associated with volcanic eruptions include lava flows, falling ash and projectiles, mudflows, and toxic gases. Volcanic activity may also trigger other natural hazardous events including local tsunamis, deformation of the landscape, floods when lakes are breached or when streams and rivers are dammed, and tremor-provoked landslides.
Tsunamis from tectonics and landslides
Tsunamis are long-period waves generated by disturbances such as earthquakes, volcanic activity, and undersea landslides. The crests of these waves can exceed heights of 25 meters on reaching shallow water. The unique characteristics of tsunamis (wave lengths commonly exceeding 100 km, deep-ocean velocities of up to 700 km/hour, and small crest heights in deep water) make their detection and monitoring difficult. Characteristics of coastal flooding caused by tsunamis are the same as those of storm surges.
An avalanche occurs when a large snow (or rock) mass slides down a mountainside.An avalanche is an example of a gravity current consisting of granular material. In an avalanche, lots of material or mixtures of different types of material fall or slide rapidly under the force of gravity. Avalanches are often classified by the size or severity of consequences resulting from the event.
Coastal erosion is a physical process by which shorelines in coastal areas around the world shift and change, primarily in response to waves and currents that can be influenced by tides and storm surge. Coastal erosion can result from long-term processes (see also beach evolution) as well as from episodic events such as tropical cyclones or other severe storm events.
A lahar is a type of natural event closely related to a volcanic eruption, and involves a large amount of material originating from an eruption of a glaciated volcano, including mud from the melted ice, rock, and ash sliding down the side of the volcano at a rapid pace. These flows can destroy entire towns in seconds and kill thousands of people, and form flood basalt. This is based on natural events.
A sinkhole is a localized depression in the surface topography, usually caused by the collapse of a subterranean structure such as a cave. Although rare, large sinkholes that develop suddenly in populated areas can lead to the collapse of buildings and other structures.