GLOSSARY - Physical Geography - page 152

Divergent plate boundaries Where two tectonic plates move apart
and create new crust, leading to features such as the ocean floor, a mid-
ocean ridge and rift valleys.
Drumlins Streamlined mounds of till in the direction of ice flow, with
a blunt upstream end and a tapered downstream end.
Dry adiabatic lapse rate Air is a poor conductor of heat, therefore the
cooling or warming of an air parcel is considered to be adiabatic (self-
contained) as there is no exchange of energy between the air parcel
and the surrounding atmosphere. The dry adiabatic lapse rate is 9.8°C
per kilometre and applies only to air parcels that have not reached dew
point, at which condensation occurs and the saturated adiabatic lapse
rate is applied.
Ecological footprint An estimation of the amount of ecological
resources used by an individual, company or nation.
Ecological niche Where there are no competitors for any of the
resources required by an organism, it can occupy the ideal conditions
to which it is adapted within that ecological community. No two
organisms can occupy the same niche.
Ecosystem services Services provided by ecosystems that support
human life in some way, e.g. food, medicine and clean water. Evaluat-
ing these services helps to focus public attention on environmental
issues that could result in the loss of these services.
El Niño Southern Oscillation A reduction in upwelling of cold deep
water in the South American Pacific resulting from reduced strength of
trade winds over the equatorial Pacific Ocean, which in turn reduces
the strength of westward-driven currents. This leads to unseasonal
warm weather and disruption of pressure and precipitation systems in
the southern hemisphere approximately every 5 years.
Environmental lapse rate The normal rate of temperature change
with altitude. Air temperature falls by approximately 6.4°C per kilo-
metre, but is subject to variation.
Erratics Large boulders that have been transported a long distance from
their original source by glacial ice.
Eskers A long, narrow, wavy ridge containing fine material transported
by R-channels at the glacier bed. Eskers can be 20 to 30 metres high
and up to 500 kilometres in length.
Evapotranspiration The movement of water (liquid) from the Earth's
surface into the atmosphere (as water vapour) by evaporation plus tran-
spiration from plants (see definition below).
Fjord A deep valley carved out by a glacier which has now become
inundated by water from the sea.