Barrier islands. Elongate bodies of sand thrown up by parallel to a coast line by the waves.

Barrier reef. A long ridge of coral near and parallel to the coast line, separated from it by a lagoon.

Barrier rollover. Response by barrier islands to rising sea level through erosion on their oceanic sides and deposition of the material by overwash on their back sides.

Blowout. Depressions formed by wind in sandy areas where the vegetation has been removed.

Coral reefs. A ridgelike or moundlike structure composed of corals and other aquatic organisms, occurring in shallow water along some subtropical and tropical shorelines.

Debris flows. Very rapid downslope movement of rock and regolith.

Deflation. Wind erosion of sediments.

Deflation basin. A depression formed as wind blows sand from a surface unprotected by vegetation.

Delta. A depositional plain formed by a river as it enters a standing body of water, such as a lake or the ocean.

Diversion culverts. Channels that are excavated along the top of a slope to intercept water flow and protect the lower slope from erosion.

Dormant volcano. A volcano that has not erupted within historic time but is capable of erupting in the future.

Dunes. A rounded hill or ridge of sand heaped up by the action of the wind.

Ebb surge. The return of flood surge waters, stream flow and precipitation back into the ocean as a hurricane moves inland.

Ebb surge channels. Roads, driveways, and channels perpendicular to the coast that channel hurricane flood flow across the shore back into the ocean.

Effluent streams. Streams that receive most of their discharge from the ground water table.

Extinct volcano. A volcano that is not expected to erupt again.

Eye. The center of a hurricane, an area of relative calm and very low pressure.

Eyewall. The area just outside of the eye of a hurricane, which is the location of the greatest turbulence and highest winds.

Fetch. The distance over which wind blows.

Fissure eruptions. The ejection of lava from a crack rather than a vent.

Flood. An overflowing of water beyond the channel’s capacity.

Flood barrier. A moveable wall or series of gates that can close off a waterway to protect it from hurricane storm surge.

Flood frequency recurrence curve. A graph that expresses in years the likelihood of development of a flood of a given height.

Flood hazard map. This map shows areas that would be flooded by stream discharges of a given magnitude (for example, a "50-year flood").

Flood impoundment dam. A containment structure that holds rainwater so it can be released slowly after a flood.

Floodplain. The flat plain on either side of a stream that is flooded periodically.

Flood tide. Landward flow of estuarine water with the rise of the incoming tide.

Floodwalls. Reinforced concrete structures parallel to the river banks which prevent floodwaters from inundating the settled areas behind them.

Foreshocks. A small seismic event preceding a greater one and originating at or near the same place, caused by minor breaks in stained rocks, especially along tributary faults.

Fringing reef. A coral reef growing outward from the shore with no open water between it and the shore.

Greenhouse effect. The process by which increases in natural and anthropogenic carbon dioxide and other atmospheric gases have trapped more and more of Earth’s heat, thus increasing atmospheric temperatures.

Groins. Walls of rock, concrete, or wood built perpendicular to the land into the surf zone to trap sand and build up beaches.

Hazard map. A map showing areas that are affected by a particular hazard such as lava flows or stream flooding.

Hermatypic. Reef-building corals in which the coral animals live in a symbiotic association with algae.

Hurricane. A massive low pressure system of tropical origin with rotary winds that exceed 119 kilometers per hour (74 miles per hour) blowing counterclockwise around a relatively calm central area called the eye.

Intermittent streams. Streams that flow only part of the year, when the groundwater table rises to fill their channels.

Jetties. Long rock or concrete structures built into the surf zone on either side of a tidal inlet to prevent the inlet from closing through deposition of sand carried along the coast by longshore drift.

Lateral erosion. The sideward erosion by a stream as it migrates over its floodplain with time.

Lava. Molten rock that has extruded on to Earth’s surface.

Lava dome. A volcano built up of viscous lava that does not flow far from the vent before it solidifies.

Lava flow. Magma that reaches the surface non-explosively and spreads out.

Levee. A ridge of sediment deposited alongside a stream as floodwaters rising out of the channel lose energy and deposit their coarser load.

Longshore drift. Movement of sediment along a shoreline by successive waves.

Magma. Molten rock beneath Earth’s surface.

Mercalli scale. A scale to measure the intensity of an earthquake as perceived by humans.

Mudflows. Mud containing significant water (up to 30 percent) and a large proportion of fine-grained material.

Overwash. Sediment washed by storm waves through low areas between dunes and onto the back side of a barrier island or inland across the mainland.

Pancaking. The process in which poured concrete floors separate from their corner fastenings and fall, floor by floor, onto each other as a result of seismic shaking.

Perennial streams. Streams that flow year round because of a high water table and humid climate.

Plate tectonics. A theory that explains the movement and deformation of parts of the outer Earth. It involves the movement of rigid lithospheric slabs, called plates, over a less rigid layer ( the asthenosphere).

Quicksand. A sand/water mixture that is fluid because water flows upward through the deposit and exerts pressure on sand grains, keeping them from touching each other.

Saffir-Simpson scale. Used to describe the relative power of a hurricane on a rating scale (category) of 1 to 5. The scale utilizes wind velocity and storm surge heights to assign a category to a given storm.

Seawall. A wall built parallel to a coast to protect it from wave erosion.

Seismograph. A detecting instrument that times and records incoming waves during an earthquake.

Seismology. A branch of geology that studies earthquakes and the passage of earthquake waves through Earth.

Sheet flow. The excess water that flows over the land surface in a layer when the rate of rainfall exceeds the infiltration rate.

Slide. A mass movement process in which rock or sediment moves downslope along a planar surface.

Storm surge. An elevation of the ocean surface resulting from the compound effects of water being pushed shoreward by wind across decreasing depths on the continental shelf, low pressure at the sea surface, tides raising the water level, and winds raising the ocean surface.

Subsidence. Sinking of the ground surface due to the removal of large quantities of water or petroleum from the pores of underlying sediments or rocks.

Tsunami. Seismic sea waves generated by a major disturbance of the sea floor and overlying water.

Washover fans. Lobe-shaped deposits of sand eroded from the ocean side of a shoreline and deposited in the bays behind the barrier island.