A protalus rampart (or pronival rampart) is a
depositional landform
Glacial landforms are landforms created by the action of glaciers. Most of today's glacial landforms were created by the movement of large ice sheets during the Quaternary glaciations. Some areas, like Fennoscandia and the southern Andes, have ...
of
periglacial
Periglaciation (adjective: "periglacial", also referring to places at the edges of glacial areas) describes geomorphic processes that result from seasonal thawing of snow in areas of permafrost, the runoff from which refreezes in ice wedges and ...
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:
* "O'er the Ramparts We Watched" is a key line from "The Star-Spangled Banner", the national anthem of the ...
). The debris may also accumulate through
avalanching or
landslide
Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated slope failures, mudflows, and debris flows. Landslides occur in a variety of environments, ...
. Protalus ramparts may be distinguished from glacial
moraine
A moraine is any accumulation of unconsolidated debris ( regolith and 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 glacier or ice sh ...
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 (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such a ...
, but suitable for this mechanism.
Protalus ramparts are recorded in the
Cairngorms
The Cairngorms ( gd, Am Monadh Ruadh) are a mountain range in the eastern Highlands of Scotland closely associated with the mountain Cairn Gorm. The Cairngorms became part of Scotland's second national park (the Cairngorms National Park) on 1 ...
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 Canal, wh ...
of
Scotland
Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to th ...
. 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, consisting 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 high ...
. Several features amongst the mountains of the
Brecon Beacons National Park
The Brecon Beacons National Park ( cy, Parc Cenedlaethol Bannau Brycheiniog) is one of three national parks in Wales, and is centred on the Brecon Beacons range of hills in southern Wales. It includes the Black Mountain ( cy, Y Mynydd Du) in ...
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 (''Y Mynydd Du'') in the Brecon Beacons National Park (''Parc Cenedlaethol Bannau Brycheiniog'') in southern Wales. It is a subsidiary summit of Fan Brycheiniog. It falls within the coun ...
, 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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