Progradation
Encyclopedia
In sedimentary geology and geomorphology
Geomorphology
Geomorphology is the scientific study of landforms and the processes that shape them...

, the term progradation refers to the growth of a river delta
River delta
A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river...

 farther out into the sea over time. This occurs when the mass balance
Mass balance
A mass balance is an application of conservation of mass to the analysis of physical systems. By accounting for material entering and leaving a system, mass flows can be identified which might have been unknown, or difficult to measure without this technique...

 of sediment into the delta is such that the volume
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....

 of incoming sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

 is greater than the volume of the delta that is lost through subsidence
Subsidence
Subsidence is the motion of a surface as it shifts downward relative to a datum such as sea-level. The opposite of subsidence is uplift, which results in an increase in elevation...

, sea-level rise, and/or erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...

. As a result, progradation is most common:
  • during periods of sea-level fall which results in marine regression
    Marine regression
    Marine regression is a geological process occurring when areas of submerged seafloor are exposed above the sea level. The opposite event, marine transgression, occurs when flooding from the sea covers previously exposed land....

    . This can occur during major continental glaciations within ice age
    Ice age
    An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...

    s, periods during which mass anomalies cause the local geoid to rise, and due to an overall deepening of ocean basins that can often be caused by the presence of older, deeper sea floor.
  • with extremely high sediment input, such as in the Yellow River
    Yellow River
    The Yellow River or Huang He, formerly known as the Hwang Ho, is the second-longest river in China and the sixth-longest in the world at the estimated length of . Originating in the Bayan Har Mountains in Qinghai Province in western China, it flows through nine provinces of China and empties into...

     in China
    China
    Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

    , which drains the loess plateau
    Loess Plateau
    The Loess Plateau , also known as the Huangtu Plateau, is a plateau that covers an area of some 640,000 km² in the upper and middle reaches of China's Yellow River. Loess is the name for the silty sediment that has been deposited by wind storms on the plateau over the ages...

    .

See also

  • Retrogradation
    Retrogradation
    Retrogradation is the term for the landward change in position of the front of a river delta with time. This occurs when the mass balance of sediment into the delta is such that the volume of incoming sediment is less than the volume of the delta that is lost through subsidence, sea-level rise,...

  • River delta
    River delta
    A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river...

  • Aggradation
    Aggradation
    Aggradation is the term used in geology for the increase in land elevation due to the deposition of sediment. Aggradation occurs in areas in which the supply of sediment is greater than the amount of material that the system is able to transport...

  • Marine transgression
  • Marine regression
    Marine regression
    Marine regression is a geological process occurring when areas of submerged seafloor are exposed above the sea level. The opposite event, marine transgression, occurs when flooding from the sea covers previously exposed land....

  • Sedimentology
    Sedimentology
    Sedimentology encompasses the study of modern sediments such as sand, mud , and clay, and the processes that result in their deposition. Sedimentologists apply their understanding of modern processes to interpret geologic history through observations of sedimentary rocks and sedimentary...

  • Stratigraphy
    Stratigraphy
    Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....

  • Sequence stratigraphy
    Sequence stratigraphy
    Sequence stratigraphy is a branch of geology that attempts to subdivide and link sedimentary deposits into unconformity bound units on a variety of scales and explain these stratigraphic units in terms of variations in sediment supply and variations in the rate of change in accommodation space...

  • Sediment transport
    Sediment transport
    Sediment transport is the movement of solid particles , typically due to a combination of the force of gravity acting on the sediment, and/or the movement of the fluid in which the sediment is entrained...

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