Cobble (geology) in the context of "Evaporite"

In geography and geology, fluvial sediment processes or fluvial sediment transport are associated with rivers and streams and the deposits and landforms created by sediments. It can result in the formation of ripples and dunes, in fractal-shaped patterns of erosion, in complex patterns of natural river systems, and in the development of floodplains and the occurrence of flash floods. Sediment moved by water can be larger than sediment moved by air because water has both a higher density and viscosity. In typical rivers the largest carried sediment is of sand and gravel size, but larger floods can carry cobbles and even boulders.When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluvioglacial is used, as in periglacial flows and glacial lake outburst floods. Fluvial sediment processes include the motion of sediment and erosion or deposition on the river bed.

A desert pavement, also called reg (in western Sahara), serir (in eastern Sahara), gibber (in Australia), or saï (in central Asia) is a desert surface covered with closely packed, interlocking angular or rounded rock fragments of pebble and cobble size. They typically top alluvial fans. Desert varnish collects on the exposed surface rocks over time.

Geologists debate the mechanics of pavement formation and their age.

Substrate is the earthy material that forms or collects at the bottom of an aquatic habitat. It is made of sediments that may consist of:

• Silt – A loose, granular material with mineral particles 0.5 mm or less in diameter.
• Clay – A smooth, fine-grained material made of fine particles of hydrous aluminium phyllosilicate minerals (such as kaolinite).
• Mud – A mixture of water with silt, clay, or loam.
• Sand – Mineral particles between 0.06 and 2 mm in diameter.
• Granule – Between 2 and 4 mm in diameter.
• Pebble – Between 4 – 64 mm in diameter.
• Cobble – between 6.4 and 25.6 cm in diameter
• Boulder – more than 25.6 cm in diameter.
• Other, assorted organic matter, detritus.

Stream substrate can affect the life found within the stream habitat. Muddy streams generally have more sediment in the water, reducing clarity. Clarity is one guide to stream health.

A pebble is a clast of rock with a particle size of 4–64 mm (0.16–2.52 in) based on the Udden-Wentworth scale of sedimentology. Pebbles are generally considered larger than granules (2–4 mm (0.079–0.157 in) in diameter) and smaller than cobbles (64–256 mm (2.5–10.1 in) in diameter). A rock made predominantly of pebbles is termed a conglomerate. Pebble tools are among the earliest known man-made artifacts, dating from the Palaeolithic period of human history.

A beach composed chiefly of surface pebbles is commonly termed a shingle beach. This type of beach has armoring characteristics with respect to wave erosion, as well as ecological niches that provide habitat for animals and plants.

A shingle beach, also known as either a cobble beach or gravel beach, is a commonly narrow beach that is composed of coarse, loose, well-rounded, and waterworn gravel, called shingle. The gravel (shingle) typically consists of smooth, spheroidal to flattened, pebbles, cobbles, and sometimes small boulders, generally in the 2 to 20 centimetres (0.8 to 7.9 in) size range. Shingle beaches typically have a steep slope on both their landward and seaward sides. Shingle beaches form in wave-dominated locations where resistant bedrock cliffs provide gravel-sized rock debris. They are also found in high latitudes and temperate shores where the erosion of Quaternary glacial deposits provide gravel-size rock fragments. This term is most widely used in Great Britain.

While this type of beach is most commonly found in Europe, examples are also found in Bahrain, North America, and a number of other world regions, such as the west coast of New Zealand's South Island, where they are associated with the shingle fans of braided rivers. Though created at shorelines, post-glacial rebound can raise shingle beaches as high as 200 metres (660 ft) above sea level, as on the High Coast in Sweden.

In geology, a boulder (less commonly spelled bowlder) is a rock fragment with size greater than 25.6 cm (10.1 in) in diameter. Smaller pieces are called cobbles and pebbles. While a boulder may be small enough to move or roll manually, others are extremely massive. In common usage, a boulder is too large for a person to move. Smaller boulders are usually just called rocks or stones.

Grain size (or particle size) is the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. This is different from the crystallite size, which refers to the size of a single crystal inside a particle or grain. A single grain can be composed of several crystals. Granular material can range from very small colloidal particles, through clay, silt, sand, gravel, and cobbles, to boulders.