Geomorphology is the study of changing landforms. Landforms are always changing,
sometimes quickly and sometimes slowly. Some processes build landforms up while
others modify them as can be seen in the diagram on screen. The Earth's landforms
are built up by the processes of volcanism, folding and faulting. Folding is where
crustal plates move together forcing rocks between them to fold as
can be seen at the diagram on screen. The mountain ranges formed are the most common
type. Much of the hill country in the North Island of New Zealand is the result of
folding, such as the Kaimanawa ranges which have buckled due to the coming
together of the Pacific and Indo-Australian plates. Faulting occurs where
there's a crack in the Earth's crust known as a fault. Most movement of land
by these faults are slow, but a sudden movement can result in an earthquake.
Depending on the direction of movement, land can move in an upwards, downwards or
sideways direction. For example, the Southern Alps of New Zealand have been
formed by uplift of land alongside the Alpine Fault. Volcanism is where cracks
in the Earth's crust allows magma to reach the surface for a volcanic
eruption, where cools and hardens to become a volcano. For example these
mountains in the Tongariro National Park which is located in the central North
Island of New Zealand.
Land is then modified by various erosion processes. The removal of soil
and rock is called weathering. The transportation of the material is
usually down-slope due to gravity, and the deposition of material results of
deposition landforms. Some of these natural processes include the actions of
wind, rivers, glaciers, waves and the freezing and falling of ice.
Erosion by wind is known as Aeolian erosion. This type of erosion is
significant in environments where the soil is unconsolidated such as beaches
and deserts. Wind transports the fine particles and
deposit them as dunes. Erosion by rivers is called fluvial erosion.Streams and rivers
erode rocks and soil from riverbeds and banks and typically deposits the
material downstream on the floodplains of river valleys or in deltas. The clay,
silt, sand and gravel deposited by flowing streams is known as alluvium.
Glaciers are rivers of ice. They erode by grinding the rocks and transport enormous
quantities of debris as they move down-slope. They carve out U-shaped valleys such as
these examples in Fiordland. Material deposited at the side and terminus of
the glacier are called moraines.
Erosion by the freezing and thawing of water is known as periglacial erosion.
This is significant in alpine regions where water gets into the cracks in
rocks. The daily or seasonal freezing and thawing can cause the rocks to shatter.
Ocean waves are an agent of coastal erosion. Through processes like abrasion,
hydraulic action and corrosion, waves break down rocks into finer sediments
like sand and transport the material along beaches. Deposition features
that result from the transportation of sediment include beaches, spits, bars, tombolos
and mud flats. Wave erosion leaves behind features such as cliffs,
wave cut platforms, caves, arches and stacks. Mass movement also known as mass
wasting is when large quantities of soil and rock move down-slope by the force of
gravity. Sometimes this process can happen slowly as in the process of soil
creep. Other times it can be quick when there is a landslide, a lahar or an
avalanche. Factors that can increase the potential for mass wasting include an
increase of water content in the soil, a reduction in the vegetation that holds
the soil together, the undercutting of a slope by either erosion or excavation, and
by earthquakes.