- Summary sheet on the Peruvian coastline as an example of both features of submergence and emergence (including marine platforms and raised beaches)
- Key detail with statistics and diagrams
- A* Grade
- Used as an example in the Coasts module of AQA A Level Geography, as required in the specif...
Peru is a country on the central western coast of South America facing
the Pacific Ocean. It lies wholly in the Southern Hemisphere, and
borders Brazil, Ecuador, Chile, Colombia and Bolivia.
Natural hazards that Peru experiences include earthquakes, tsunamis,
flooding, landslides, and mild volcanic activity. The position of Peru
adjacent to the subduction zone of the Nazca and South American
tectonic plates - converging in the Atacama trench off the Pacific coast -
serves as the catalyst to many of Peru's natural hazards.
The formation of coastal features in Peru is a result of a combination of
tectonic uplift and eustatic sea level change.
The Pacific coast is well known for its tectonic activity and has led
to the formation of the Andes Mountain range and the Peru-Chile
Trench. As it is a zone of subduction, uplift is common, but the rate
of uplift has varied over the last 2 million years, and it is not uniform
along the coast.
In the southern coast, marine terraces and raised beaches provide
evidence for tectonic uplift and emergence along the southern coast.
The marine terrace indicates there was a former coastline, and there
are wave cut platforms created by wave erosion. Sand and shells can
be deposited on the beach. The terraces have a flat platform, a
raised beach with fossil cliffs behind, almost giving the appearance
of a staircase.
The highest marine terrace is 780 metres high. There are
27 marine terraces in total, and over the last 125,000
years, uplift rates have been estimated at an average of
700 mm per 1,000 years. The highest rate has been dated
using marine fossils and is estimated to be 2 million years.
The proximity of the Nazca ridge, an oceanic ridge which
lies perpendicular to the coast, plays a significant role in
the rate of uplift. Tectonic uplift has likely occurred in
spurts rather than continuous motion.
Sea level change are significant as in the last 2 million years glacial
and interglacial cycles have dramatically influenced sea levels. Sea
levels do not remain constant and can be affected by tectonic
deformation, isostatic movements, capacity of the ocean basin, and
the melting of ice sheets. During an interglacial period, it is possible
to raise sea levels by 65 metres above present levels, and during
glacial periods, it can fall by 210 metres. Because the scale of the
terraces is greater than 65 metres above present sea level, the
features must be related to tectonic uplift.
Accounting for the causes of emergence and submergence are
complicated as events may occur at the same time.
Similar landforms may have been created by different processes is
known as equifinality. The south coast of Peru is thought to be a
result of tectonic forces, but along the central part of the coast,
eustatic variations are more important.
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