The term felsenmeer comes from the German meaning 'sea of rock'. In a felsenmeer (also known as a block field), freeze-thaw weathering has broken up the top layer of the rock, covering the underlying rock formation with jagged, angular bolders. Freeze-thaw weathering occurs when water that is trapped along microcracks in rock expands and contracts due to fluctuations in temperature above and below the freezing point. Felsenmeers are formed in situ, meaning that they are not transported during or after their creation.
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Felsenmeers only form on slopes of 25° or lower. A steeper angle results in transport of the blocks due to gravity. This creates a talus slope, rather than a felsenmeer.[1] Crude sorting with boulder imbrication can occasionally be seen on the surface of felsenmeers.
The depth of the boulder field depends on the slope angle, rock types, age, and erosional history. However, a reasonable average for felsenmeer depth is approximately 1m. Ballantyne (1998) [2] defines three types of felsenmeer profiles: Type 1 consists of boulders overlying a matrix of fines at some depth below the surface. Type 2 consists of boulders supported by a cohesionless sandy matrix that continues from the surface down through the profile. Type 3 also consists of boulders supported by a matrix, but differs from Type 2 in that the matrix consists of silt and/or clay rather than sand.
Felsenmeers are most often found in high mountain periglacial regions near the Arctic Circle, especially in Iceland, the Canadian arctic and Norway. Due to the slope requirements they are most commonly found on plateaus. Basalt and sedimentary rocks often produce larger, more numerous felsenmeers than other types of rock.
Felsenmeers are, typically, relatively young geomorphological features. Most felsenmeers formed during or since last ice age (approximately 20,000 years ago). Their specific age can be determined using surface exposure dating, a technique that works best on materials which have been exposed to cosmic rays with little interference from trees or soils.