Hazardous Environments

• Ash fallout


  The deposition of ash and other volcanic material following a volcanic eruption.
• Benioff zone


  A narrow zone of deep earthquake foci at a subduction zone.
• Continental crust


  That part of the Earth's crust that forms the continents.
• Hot spot


  A relatively small area where magma rises through a continental or ocean plate. As the plate moves across the hot spot a chain of volcanoes may form.
• Lava


  Molten magma that has reached the earth's surface. It may be liquid, or may have solidified.
• Lithosphere


  The outermost layer of the Earth comprising the crust and part of the mantle.
• Magma


  Molten rock within the Earth; when it reaches the surface it is called lava.
• Mid-ocean ridges


  Lines of mainly mountains formed where two ocean plates are separating.
• Nuee ardente


  An incandescent cloud of gas that sometimes accompanies pyroclastic flows.
• Oceanic crust


  That part of the crust underlying the oceans. It is basaltic in composition.
• Pyroclastic flow


  A fast-moving cloud of extremely hot gas, ash and rock fragments, which can reach temperatures of about 1 000 °C and travel at speeds of up to 700 km/h.
• Richter Scale


  An open-ended scale to record magnitude of earthquakes.
• Subduction zone


  The area where one plate slides beneath another; a zone of earthquakes and melting.
• Tephra


  Solid material, whatever its size, ejected from a volcano, and often called pyroclastic material.
• Transform fault


  Where two plates slide past each other; like a tear fault on a larger scale.
• Tuff


  Refers to fine particles of tephra (up to 4 mm in diameter).
• Volcanic bomb


  A fragment of molten lava (over 4 mm in diameter) thrown from a volcano.
• Mass movement


  Any large-scale movement of the Earth's surface that is not accompanied by a moving agent.
• Landslide


  A movement of a mass of rock, earth or debris down a slope. Landslides are divided into the following types of movement: falls, slides and

  flows.
• Mudslide


  A rapid (up to 80 km/h) and fluid type of mass movement. It is a rapid movement of a large mass of mud formed from loose material and water.
• Shear stress


  Refers to the forces trying to pull a mass downslope.
• Shear resistance/strength


  the internal resistance of a slope.
• Regrading


  The levelling of steep slopes into gentler ones.
• Avalanche


  a rapid mass movement consisting of snow, ice, rock and debris.
• Wet avalanche


  An avalanche consisting of partially melted snow.
• Dry avalanche


  An avalanche consisting of fresh snow that has fallen off older snow.
• Fujita Scale


  A scale devised by Dr Theodore Fujita to measure damage done by tornadoes. It varies from T0 (winds less than 73 mph) with little damage, to F5 (winds greater than 261 mph) with 'incredible damage'.
• Mesocyclone


  A large-scale region of rotation, typically around 3-8 km in diameter and often found in the rear flank of a supercell. The circulation of a mesocyclone covers an area much larger than the tornado that may develop within it.
• Supercell tornado


  A tornado associated with large, long-lived thunderstorms, possessing strong mid-level rotation. (Nonsupercell tornadoes are smaller but may still contain damaging winds in excess of 120 knots.)
• Tornado


  A violent, destructive weather system, with powerful rotating winds (up to 300 km/h). Tornadoes are intense lowpressure systems, and their development depends on instability in the atmosphere, convergence and strong updrafts in the air.
• Vortex


  A whirling and rising mass of air and cloud in a tornado
• Hurricane


  A tropical storm that forms over the North Atlantic, with winds over 74 mph (120 km/h).
• Tropical storm

  The generic name to include hurricanes (North Atlantic), cyclones (Indian Ocean and the Bay of Bengal) and typhoons (Japan). A tropical cyclone is a low-pressure system commonly up to 600 km in diameter with wind speeds of up to 300 km/h (typically 160 km/h) and bringing up to 30-50 cm of rainfall.
• Bioengineering


  The use of vegetation in engineering, e.g. the selection of plant species for the recolonisation of areas following landslides.
• Geo-materials


  Refer to the use of naturally occurring materials such as vegetation in engineering.
• Geostructures


  Structures constructed from geo-materials such as bamboo bundles (fachines), coir rolls and straw wattles.
• Hazard mapping

  The process of determining when and where hazards have occurred in the past, their frequency and magnitude and their likely impacts.
• Risk assessment


  The process of establishing that a hazardous event of a particular magnitude will occur within a given period and estimating its impact, taking into account the location of buildings, facilities and emergency systems.
• Seismometer


  An instrument used for measuring earthquakes.