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Adiabatic Lapse Rate. The rate at which air temperature
decreases with elevation because of the decreasing
effect of gravity. The result is an increase in air volume
without any change in the total amount of heat. The
normal adiabatic lapse rate is -1 °C for each 100 metres
of elevation: but the saturated adiabatic lapse rate,
when air cools more slowly, is 0.4-0.9°C per
100 metres. If a parcel of air is moved towards the
ground the reverse process occurs and the air begins to
Agglutinate. The tendency for high-pressure cells
originating from the poles to stagnate and stack up at a
particular location over mid-latitude oceans. The
Bermuda or Azores High represents one of these
locations at which stagnation tends to occur. See
Mobile Polar High.
Albedo. The degree to which short wave solar radiation is
reflected from any surface or object.
Andesite. Volcanic rock containing the minerals
andesine, pyroxene, hornblende, or biotite. In a melted
state, such material contains a high amount of
dissolved gas.
Aperiodically. Recurring but not with a fixed regularity.
For instance, the first day of each month occurs
aperiodically because there are not the same number
of days in every month.
Aseismic. Characterizing a region that historically has not
experienced earthquakes.
Atterberg Limits. These limits define the moisture
content of a soil at the points where it becomes elastic,
plastic, and liquid.
Barrier Island. A sandy island formed along a coastline
where relative sea level is rising or has risen sub-
stantially in the past. Shoreward movement of
sediment cannot shift the island landward fast enough,
so the island becomes separated from the mainland by
a lagoon or marsh.
Basaltic. Referring to the most common liquid rock
produced by a volcano, containing mainly magnesium,
iron, calcium, aluminum, and some silicon. It forms a
hard, but easily weathered, fine-grained, dark-grey rock.
Volcanoes producing magma with these constituents are
classified as basaltic.
Base Surge. The sudden eruption of a volcano laterally
rather than vertically.
Bathymetry. Depths below sea level.
Bearing Strength. The amount of weight that a soil can
support, including its own weight, before the soil
deforms irrevocably.
Benioff Zone. The zone at a depth of 700 km associated
with earthquakes along a subduction zone.
Biomass. The total weight of all living organisms.
Bistable Phasing. Over two to three centuries in many
locations, droughts and wet periods tend to alternate
every 9.3 years. In some cases, a drought is suddenly
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