Cobble (geology)

Boulders ( to roll ) consists of stones, so rock debris, which are moved during transport by water, landslides, mudslides or other ground movement to the valley and the broken edges were doing more or less rounded.

The size of the stones is mainly 2-20 centimeters, according to DIN 4022 cobbles greater than 63 mm, generally at least greater than 2 mm ( Psephite ), block rubble in size to about house size. Smaller particle sizes are called gravel.

Distinction

In principle, a distinction is made

• Fluviatile debris ( debris flow ) Small boulders in a river bed is referred to as gravel; close to the water can be heard as a quiet murmur or singing his movement. It often forms large gravel or gravel banks, which serve as important raw materials for the construction industry because of its uniform composition of the grain sizes. Individual large blocks called there Schroppen.
• Marine debris ( scree surf )
• Glacial boulders: moraines, boulders and sediment
• Rubble rubble, the mixed form of debris and rubble, posing as foot ( talus ) around rock towers, along the cliffs and in Karen and steep valleys attaches - these are the rubble critical angle, fresh quarry can not remain lying and rolls as rock fall into the valley. In the talus is moved slowly through frost work.
• Rieselfluh, connected by loose earth rubble
• Pyroclastic boulders.

Further

• Scree: They are formed from passive wind sediments by the korrasive effect of wind and sand from previously sharp rock fragments ( to abraded cobbles reshaped ) arise.

Sedimented and the material solidifies, creating a conglomerate ( in distinction to the edged breccia ). Therefore, include cobbles to the clastic sediments. A special form of such rocks are the tillites.