Physical Geography

A traveler crossing the International Date Line eastbound subtracts one day, or 24 hours, so that the calendar date to the west of the line is repeated. Crossing the IDL westbound results in 24 hours being added, advancing the calendar date by one day. The International Date Line is necessary to have a fixed, albeit arbitrary, boundary on the globe where the calendar date advances in the westbound direction.

A levee is an elongated naturally occurring ridge or artificially constructed fill or wall, which regulates water levels. It is usually earthen and often parallel to the course of a river in its floodplain or along lowlying coastlines.

A moraine is material left behind by a moving glacier. This material is usually soil and rock. Just as rivers carry along all sorts of debris and silt that eventually builds up to form deltas, glaciers transport all sorts of dirt and boulders that build up to form moraines.

The Himalaya are among the youngest mountain ranges on the planet and consist mostly of uplifted sedimentary and metamorphic rock. They are Fold Mountains which were formed due to a continental collision or orogeny along the convergent boundary between the Indo-Australian Plate and the Eurasian Plate.

The Earth rotates around its axis once in about 24 hours with respect to the sun and once every 23 hours 56 minutes and 4 seconds with respect to the stars. The Earth rotates from the west towards east. Seasons are caused by Earth’s rotation around its axis.

Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth’s atmosphere, biota and waters. Weathering occurs in situ, or “with no movement.”

Hydraulic action is one of the main forms of river erosion (example of erosion due to running water) in which the force of the river against the banks can cause air to be trapped in cracks and crevices. The pressure weakens the banks and gradually wears it away.

A rift valley is a linear-shaped lowland between several highlands or mountain ranges created by the action of a geologic rift or fault. It is formed by the subsidence of a segment of the Earth’s crust between dip-slip, or normal, faults.

An earthquake is also known as a quake, tremor or temblor. At the Earth's surface, earthquakes manifest themselves by shaking and sometimes displacement of the ground. It is the result of a sudden release of energy in the Earth's crust that creates seismic waves.

Earthquakes result from the sudden release of energy in the Earth’s crust that creates seismic waves. Most occur along plate boundaries. Tectonic earthquakes occur anywhere in the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane.

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