Outline the main mechanisms by which surface processes transport sediments and discuss how these processes control the characteristics of the deposits that they lay down
This Essay will summarize the main mechanisms by which sediment is transported over the surface and evaluate how those processes influence the characteristics of the depositions.
Sediments are particles of former rocks which have been eroded over time. The eroded material is then transported by different processes onto the landscape sometimes over very far distances.
There are three major types of sediments, one are clastic sediments which are composed of rock particles. Additionally Sediments form from organic materials such as dead organism and other collections of organisms which are often organic rich and contribute to a more fertile landscape. Sediments are also formed through chemical processes such as minerals like salt in rain.
Sediment can eventually become rock again and thus a stable component of a landscape if put under pressure for example through being buried and then hardened. (Holden, 2005)
Sediments can enable to investigate about the forces working on the land as morphologic elements are a result of those and the material on land, eventually expressed in the form of the land. Hence a surface is shaped by the dominating climate and which surface processes will be able to work on it. The differences in temperature and precipitation all over the world will be reflected in the sediments that are deposited. (Ritter et. al, 1995)
The transportation and deposition of those particles over the earth surface is called sedimentation.
The main mechanisms which transport, erode and deposit sediments are physical processes, and the main agents are currents such as wind, water, waves and tides as well as flows induced by gravity and finally glaciers. (Reading, 1996)
The strength with which these factors operate depends on the ability of a landscape to resist the stress that is being put on it as well as the energy of the stress factor which can come from climatic conditions, tectonics and various other influences. (Holden, 2005)
As mentioned above two main mechanisms which control the transport of sediment can be identified, one of them is called current flow and the other mass flow.
Current flow can furthermore be subdivided into fluvial, aeolian and coastal transport. Generally speaking it can be said that the transport through water is the most potent or important, not necessarily in it's strength and energy level but on a longer time scale because of it's the importance for a landscape.
Water in a river system can either be laminar or turbulent. In a laminar flow water molecules move in a single path with the same velocity, contrasting to that to that the velocity oscillates continuously in all directions in a turbulent flow. Sediment grains will be transported and deposited differently depending on the strength and sort of current.
Firstly a grain can be rolled around or bounce off the bed surface, this is called a bed-load sediment. With increasing energy the current can transport a sediment in suspension.
What essentially controls if a grain is being suspended or moved by the current, is the surface area to volume ratio. (Holden, 2005)
The more energy within a current the more it has the possibility to pick up bigger particles although they weight more. Fine grains can resist if they clump together creating a bigger surface area or if they are covered by something bigger laying above them. In contrast to that fine grains which are already suspended will only accumulate under quieter currents. Since their strength to resist a current is very low they can be transported until the end of a river, whereas bigger particles are not necessarily moved all the way downstream as they rather move for a short distance and are discarded when the current reaches a critical low point. (Holden, 2005)
What additionally controls the energy
