Protalus Ramparts and the Altitude of the Local Equilibrium Line during the Last Glacial Stage in Bokspruit, East Cape Drakensberg, South Africa

Lewis, Colin A.

doi:10.2307/521318

Cited by 15 publications

(10 citation statements)

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“…() indicate that considerable fines can be transported through the process of supranival wash. Harris () suggests that fresh clean surfaces and mechanical features such as ‘conchoidal fractures, meandering ridges, breakage blocks, and arc‐shaped and parallel steps’ are characteristic of quartz grains (fines) on an active rampart in Norway. Lewis () used these and other transport‐induced microtextures of quartz grains as sedimentological evidence to identify a relict pronival rampart in South Africa. However, a recent study by Sweet and Soreghan () shows that the transport‐induced microtextures of quartz grains can be obtained through various transport/fracture processes in a variety of depositional environments and many other microtexture patterns such as dissolution etching, weathered surfaces and precipitation features can be attributed to diagenesis.…”

Section: Site Morphological and Sedimentological Characteristics Of mentioning

confidence: 99%

Diagnostic criteria for pronival ramparts: site, morphological and sedimentological characteristics

Hedding

Sumner

2013

Geografiska Annaler: Series A, Physical Geography

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ABSTRACT. Pronival ramparts are discrete debris accumulations found below steep rock faces at the foot of snowbeds or firn fields but they are often confused with moraines, protalus rock glaciers or rock-slope failure debris accumulations. This can be attributed to a poor understanding of the modes of rampart genesis, failure to recognise the significance of topography in their development and the use of inappropriate diagnostic criteria. Various characteristics have been suggested for identification of pronival ramparts but these are derived largely from relict features. Research on actively-accumulating ramparts has shown that some of the suggested criteria are no longer useful. This paper reviews existing criteria and shows that, for diagnostic purposes, more emphasis should be placed on the attributes of actively-accumulating features. A more robust set of criteria, derived from common characteristics of activelyaccumulating ramparts, are proposed that assists in discriminating relict and active pronival ramparts from other discrete bedrock cliff-foot debris accumulations.

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Section: Site Morphological and Sedimentological Characteristics Of mentioning

confidence: 99%

Diagnostic criteria for pronival ramparts: site, morphological and sedimentological characteristics

Hedding

Sumner

2013

Geografiska Annaler: Series A, Physical Geography

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“…A more impressive cirque moraine exists at Killmore ($2000 m), also in the East Cape Drakensberg. Although initially interpreted as a pro-talus rampart (Lewis, 1994), subsequent investigations concluded that a well-developed cirque moraine and pro-talus ramparts exist (Lewis and Illgner, 2001). Other work has reported only small cirque moraines on the highest mountains near the Lesotho-KwaZulu-Natal border (>3000 m), having LGM correlative ages (maximum of three dates ¼ 17 300 AE 100 14 C a BP) dated from soil organics (Mills and Grab, 2005).…”

Section: Atlas Mountains North Africamentioning

confidence: 99%

Quaternary glaciation in Africa: key chronologies and climatic implications

Mark

Osmaston

2008

J Quaternary Science

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Multiple episodes of Quaternary glaciation are evidenced on >10 distinct mountain localities throughout Africa, with the best dated sites from Kilimanjaro and Mt Kenya in equatorial East Africa. A general paucity of radiogenic dates constrains the glacial chronology, and regional sequences have largely been based on correlations by relative weathering of features. Excellent glacial moraine preservation and other features of erosion put limits on the spatial extent of palaeoglaciers, and have facilitated advances in palaeo-equilibrium line altitude (ELA) analyses. All radiocarbon dates (n < 30) provide minimum ages of deglaciation, and are consistent with a widespread synchronous advance during the Last Glacial Maximum (LGM, 21 AE 2 ka). K-Ar dates on Kilimanjaro lava flows initially recognised up to three glaciations prior to the LGM. Over 100 cosmogenic radionuclide (CRN) 36 Cl exposure ages on glacial erratics and bedrock from Kilimanjaro and Mt Kenya date 16 landforms, confirming maximum glacial extent prior to Marine Isotope Stage (MIS) 10. No glacial geological features have been dated to MIS 6. While on Kilimanjaro the CRN ages confirm a clear LGM (MIS 2) maximum, Mt Kenya lacks definitive LGM moraines. Lateglacial advances or stillstands on both mountains are suggested by low-relief moraines dating to 14.6 AE 1.2 ka (two boulders) on Mt Kenya and 16.3 AE 1.9 ka and 15.8 AE 2.5 ka on Kilimanjaro. Multiple moraines upvalley have early Holocene ages ranging from 11.2 AE 0.8 to 8.6 AE 0.2 ka. Isolated and equivocal dates on both mountains also provide speculative evidence that the maximum extent since MIS 5e may have occurred close to 30 ka, similar to sites in South America. New palaeoclimatic understanding from lake and ocean proxies suggests hypotheses for the source of low-latitude climate changes causing the advances that can be tested with improved dates. A high degree of intra-regional variance in ELA is observed, with differences by aspect reflecting precipitation gradients. Future work should include more CRN dates, improved mapping and inverse climate-mass balance modelling.

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“…A 'bench' occurs on both sides of the valley at an elevation of ~2100 m asl and is formed by a concealed, more resistant layer of basalt (Geological Survey, 1983). Located on the bench on the western side of the valley is an accumulation of boulders that were initially described as a pronival rampart by Lewis (1994;Fig. 2C).…”

Section: Site Descriptionsmentioning

confidence: 99%

The cold climate geomorphology of the Eastern Cape Drakensberg: A reevaluation of past climatic conditions during the last glacial cycle in Southern Africa

et al. 2017

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Southern Africa is located in a unique setting for investigating past cold climate geomorphology over glacial-interglacial timescales. It lies at the junction of three of the world's major oceans and is affected by subtropical and temperate circulation systems, therefore recording changes in Southern Hemisphere circulation patterns. Cold climate landforms are very sensitive to changes in climate and thus provide an opportunity to investigate past changes in this region. The proposed existence of glaciers in the high Eastern Cape Drakensberg mountains, together with possible rock glaciers, has led to the suggestion that temperatures in this region were as much as 10-17°C lower than present. Such large temperature depressions are inconsistent with many other palaeoclimatic proxies in southern Africa. This paper presents new field observations and cosmogenic nuclide exposure ages from putative cold climate landforms. We discuss alternative interpretations for the formation of the landforms and confirm that glaciers were absent in the Eastern Cape Drakensberg during the last glaciation. However, we find widespread evidence for periglacial activity down to an elevation of ~1700 m asl, as illustrated by extensive solifluction deposits, blockstreams, and stone garlands. These periglacial deposits suggest that the climate was significantly colder (~6°C) during the Last Glacial Maximum, in keeping with other climate proxy records from the region, but not cold enough to initiate or sustain glaciers or rock glaciers.

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Protalus Ramparts and the Altitude of the Local Equilibrium Line during the Last Glacial Stage in Bokspruit, East Cape Drakensberg, South Africa

Cited by 15 publications

References 0 publications

Diagnostic criteria for pronival ramparts: site, morphological and sedimentological characteristics

Diagnostic criteria for pronival ramparts: site, morphological and sedimentological characteristics

Quaternary glaciation in Africa: key chronologies and climatic implications

The cold climate geomorphology of the Eastern Cape Drakensberg: A reevaluation of past climatic conditions during the last glacial cycle in Southern Africa

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