In
sedimentary geology and
geomorphology
Geomorphology () is the scientific study of the origin and evolution of topographic and bathymetric features generated by physical, chemical or biological processes operating at or near Earth's surface. Geomorphologists seek to understand wh ...
, the term progradation refers to the growth of a
river delta
A river delta is a landform, archetypically triangular, created by the deposition of the sediments that are carried by the waters of a river, where the river merges with a body of slow-moving water or with a body of stagnant water. The creat ...
farther out into the sea over time. This occurs when the
volume
Volume is a measure of regions in three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch) ...
of incoming
sediment
Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...
is greater than the volume of the delta that is lost through
subsidence
Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope mov ...
,
sea-level rise, or
erosion
Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...
.
Progradation can be caused by:
* Periods of
sea-level fall which result in
marine regression. This can occur during major
continental glaciations within
ice age
An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and g ...
s, be caused by changes in the rates of
seafloor spreading that affects the volume of the ocean basins, or tectonic effects on the regional mantle density structure that can change the
geoid elevation.
* Extremely high sediment input, such as by the Huang He (
Yellow River
The Yellow River, also known as Huanghe, is the second-longest river in China and the List of rivers by length, sixth-longest river system on Earth, with an estimated length of and a Drainage basin, watershed of . Beginning in the Bayan H ...
) in
China
China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
, which drains the
Loess plateau, or from high sediment loads in
proglacial rivers.
See also
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References
Sedimentology
Stratigraphy
{{Stratigraphy-stub