A protalus rampart (or pronival rampart) is a
depositional landform of
periglacial
Periglaciation (adjective: "periglacial", referring to places at the edges of glacial areas) describes geomorphic processes that result from seasonal thawing and freezing, very often in areas of permafrost. The meltwater may refreeze in ice wedg ...
origin. It forms as rock debris falls onto a steep snow slope from a cliff above and slides down the snow surface to come to a rest at the foot of the slope. Over a long period of time, sufficient material can accumulate in this way to produce a distinct bank of stony material which, long after the snowbed has melted away, remains as a rampart (a bank or mound similar to a manmade
rampart
Rampart may refer to:
* Rampart (fortification), a defensive wall or bank around a castle, fort or settlement
Rampart may also refer to:
* LAPD Rampart Division, a division of the Los Angeles Police Department
** Rampart scandal, a blanket ter ...
). The debris may also accumulate through
avalanching or
landslide
Landslides, also known as landslips, rockslips or rockslides, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslides ...
. Protalus ramparts may be distinguished from glacial
moraine
A moraine is any accumulation of unconsolidated debris (regolith and Rock (geology), rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a gla ...
s by their lack of rock fragments with glacial abrasion or
striations. The morphology of the site may also suggest it being unfavourable for the development of a
glacier
A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
, but suitable for this mechanism.
Protalus ramparts are recorded in the
Cairngorms
The Cairngorms () are a mountain range in the eastern Scottish Highlands, Highlands of Scotland closely associated with the mountain Cairn Gorm. The Cairngorms became part of Scotland's second national parks of Scotland, national park (the Cairn ...
and
northwest Highlands
The Northwest Highlands are located in the northern third of Scotland that is separated from the Grampian Mountains by the Great Glen (Glen More). The region comprises Wester Ross, Assynt, Sutherland and part of Caithness. The Caledonian Cana ...
of
Scotland
Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...
. An especially large example on the north side of
Baosbheinn measures 1 km in length and reaches a height of 55 m. It is thought to result from a major rock slope failure, however evidence leads some to class it as a protalus
rock glacier
Rock glaciers are distinctive geomorphological landforms that consist either of angular rock debris frozen in interstitial ice, former "true" glaciers overlain by a layer of talus, or something in between. Rock glaciers are normally found at hi ...
. Several features amongst the mountains of the
Brecon Beacons National Park
Brecon Beacons National Park, officially named Bannau Brycheiniog National Park (), is a National parks of the United Kingdom, national park in Wales. It is named after the Brecon Beacons (), the mountain range at its centre. The national park ...
have been interpreted by some authors as protalus ramparts but as moraines by others. The depositional ridge of Fan Fechan beneath
Fan Hir
Fan Hir is a peak at the eastern end of the Black Mountain (range), Black Mountain (''Y Mynydd Du'') in the Brecon Beacons National Park (''Parc Cenedlaethol Bannau Brycheiniog'') in southern Wales. It is a subsidiary summit of Fan Brycheiniog. ...
, formerly thought to be a rampart due to its linear nature paralleling the line of the cliff above is now considered to be a moraine.
[Shakesby, R. 2002 ''Classic Landforms of the Brecon Beacons'', Geographical Association p24, 27-28, 30-37 ]
References
Glaciology
Geology of Scotland
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