Paul Sumner

The maritime Subantarctic: a distinct periglacial environment

Recent research on slope processes and weathering on Marion Island has highlighted distinctive attributes of the maritime Subantarctic periglacial environment, compared to other periglacial environments. This is reflected morphologically by sorted stripe characteristics and stratified solifluction forms, but the wind factor and low diurnal temperature range also results in differences with other diurnal frost environments. Its hyper-maritime setting at low mean annual temperatures results in very high frost cycle frequencies, with associated effectiveness in surface sediment transport and patterned ground development. In addition, a high frequency of wetting and drying cycles is observed in rocks. Small seasonal temperature ranges and steep temperature profiles indicate a high sensitivity to climate change in the Subantarctic, as reflected in a rich relict periglacial record on most islands. This sensitivity appears absent in high tropical environments of low annual temperature range.

Rainfall and temperature attributes on the Lesotho–Drakensberg escarpment edge, southern Africa

Abstract. Located near the southeastern limit of Africa, the Lesotho‐Drakensberg and associated escarpment is the highest range of African mountains south of the massifs in Tanzania. At the escarpment summit and on the adjacent high peaks, the climate is generally interpreted as marginal periglacial yet few data, specifically rainfall and temperature, exist on record at these altitudes. Climatic data from two temporary field stations on the escarpment edge, one of which is the highest rainfall station yet on record in southern Africa, provide contemporary surface‐climate conditions. Mean annual rainfall recorded between 2001 and 2005 averages 767.8 mm at Sani Pass summit (three complete years), and 753.2 mm on Sentinel Peak (two complete years); these values are less than those recorded for the same period in the mountain foothills. Even though rainfall is slightly below long‐term rainfall averages for the area due to a marginally dry spell, the data show that earlier estimates of between 1000 mm and 2000 mm rainfall per annum on the escarpment are too high. A measured mean air temperature of 5.8°C at Sani Pass, however, falls within the range estimated for the escarpment summit. Frost cycles in air and at the soil surface are frequent in winter, but absent in soil for summer, and no long‐duration surface‐soil freeze was measured. Temperatures thus confirm the marginal periglacial nature as postulated for previously, but precipitation data indicate a dryer environment than anticipated. Palaeoenvironmental scenarios, notably arguments for former glaciation based on extrapolations from somewhat exaggerated contemporary precipitation values, thus require re‐consideration.

Geomorphological characteristics of small debris flows on Junior's Kop, Marion Island, maritime sub ‐ Antarctic

The geomorphological characteristics of small debris flows in a maritime sub-Antarctic environment are described. The morphological and sedimentological characteristics of the debris flows are comparable to debris flows documented for other parts of the world; their initiation appears closely linked to the unusual environment in which they are found. Sediment supply is generated by diurnal frost heave of loamy sediment associated with Azorella selago. The debris flows are triggered by sediment mobilization upon saturation of the frost-heaved surface gravel and overland flow over the low-permeability and frost-susceptible slope materials. Morphological effects of the flows are short-lived due to obliteration by subsequent frost heave activity. Copyright

TRENDS IN RAINFALL TOTAL AND VARIABILITY (1970-2000) ALONG THE KWAZULU-NATAL DRAKENSBERG FOOTHILLS

ABSTRACT South Africas most valuable source of water is the eastern escarpment region of the KwaZulu-Natal Drakensberg and Lesotho highlands. These upper catchments supply much of KwaZulu-Natal, feed the Vaal River in the interior through two inter-basin transfer schemes and are important conservation areas. Analysis of rainfall and rainfall variability trends can thus contribute to a better understanding and management of the area and yet no recent studies have investigated these aspects. This study assesses the 1970–2000 rainfall period using 13 stations to the east of the escarpment in KwaZulu-Natal and presents a spatial perspective on annual rainfall totals and intra- and inter-annual variability. Altitude and distance from the escarpment eastward are found to influence total annual rainfall with an increase of 41.5 mm per 100m in altitude between approximately 1100m and 2100m a.s.l., and a corresponding decrease of 54 mm for every 10 km eastward from the escarpment. Neither inter- nor intra-annual rainfall variability is influenced directly by altitude or the relation to the escarpment. Latitudinal position is found to have no significant affect on station totals but variability increases from south to north in the Drakensberg, possibly related to the greater seasonal contribution by frontal rains in the south, or more variable annual storm activity in the north.

Thermal Attributes of Rock Weathering: Zonal or Azonal? A Comparison of Rock Temperatures in Different Environments

Recent investigations into mechanical weathering in cold environments have highlighted products similarities to those of hot deserts. Although general temperature conditions between these two settings are obviously different on the basis of absolute air temperatures, the zonality with respect to thermal changes affecting the rock is less apparent. Data are presented here from four diverse environmental settings with particular emphasis on the fluctuating temperature regime as applicable to rock thermal stress fatigue and thermal shock. The data focus on diurnal oscillations and short-duration rapid changes on rock surfaces at sites in the Antarctic, sub-Antarctic, and at two southern African sites. Comparisons show that different climatic regimes may not be distinctive with respect to rock thermal changes. The azonality is strongly apparent when contrasting the two African sites, a hot desert and cooler alpine setting, in terms of diurnal fluctuations where very similar values are recorded. Overall temperature ranges measured at the Antarctic site approach the magnitude of those in southern Africa, and all sites show a high potential for thermal shock under rapid temperature changes. These findings highlight potential azonality with respect to thermally induced rock weathering and shift the emphasis in cross-climate comparisons to detailed considerations of the moisture regime.

ON THE NATURE OF SOUTHERN AFRICAN GEOGRAPHICAL PUBLICATIONS, 2000 TO 2004

ABSTRACT Southern African geography is assessed with respect to publication-output type, sub-discipline placement and authorship attributes for the five year period 2000 to 2004. Human geography as a sub-discipline dominates over physical geography in the number of publications produced, with a greater emphasis on single-authorship in human geography. Journal articles comprise 72% of the total outputs with more orientation towards such publications in the physical than in the human sub-discipline. Approximately two thirds of journal articles in both sub-disciplines appear in international journals. Black authors were involved in at least 22% of the outputs of which two thirds had black geographers as first author. Output alignment at the 2004 change in State subsidy qualification criteria is also considered. The discipline is found to be well- positioned to take advantage of subsidy allocation although more attention can be given to subsidy-generating journal selection, particular by human geographers. Physical geography has a slight lead in terms of National Research Foundation scientific ratings of individuals while the geographical distribution of rated scientists and a relative scarcity of young and black rated researchers is a cause for concern. The total number of publications on record appears to be reasonably healthy towards the end of the assessment period. However, geographers are challenged to focus increasingly on journal article outputs, particularly in ISI-listed journals, in order to remain aligned with South Africas international strength in the earth/environmental sciences and the improving international contribution from the social sciences.

EROSION MODELLING AND SOIL LOSS PREDICTION UNDER CHANGING LAND USE FOR A CATCHMENT ON MAURITIUS

ABSTRACT Sugarcane is the dominant form of agriculture on the island of Mauritius but the industry is facing increasing financial constraints that will probably lead to greater diversity in agriculture. Although sugarcane is considered a soil conservation crop, little is known of the current erosion rates on the island and the effect of changing crop types on sediment yields. Modelling of the potential soil loss in the Rivierre Des Anguilles, a southern catchment on Mauritius, was undertaken to obtain an understanding of the extent to which soil erosion is affected by different land use. Two erosion models are applied within a GIS framework: the Revised Universal Soil Loss Equation (RUSLE) and the Soil Loss Estimation Model of Southern Africa (SLEMSA). RUSLE is further used to predict soil loss for the catchment under three potential crop diversification scenarios. Although soil loss ranges considerably, model outputs show a similar trend in mean soil loss rates between the cropping systems in the catchment. Rates are generally highest on steep slopes (>20%) with high annual rainfall (2 400mm) along the river and in the upper catchment area. Predicted soil loss results indicate a strong inverse relationship with vegetation cover; infrequently disturbed land use types such as natural vegetation, tea and banana plantations have low soil loss values (1 to 4 t.ha−1.yr−1), whereas frequently disturbed land use types such as intercropped cane and vegetables have moderate (13 t.ha−1.yr−1) to very high (80 t.ha−1.yr−1) soil loss rates. Results show that land use change to pineapple and vegetables will have a considerable influence on soil erosion with mean soil loss for the catchment doubling and quadrupling respectively. Such crops should be confined to low slope angles and be supported by soil management practices.

Geomorphic and Climatic Implications of Relict Openwork Block Accumulations Near Thabana‐Ntlenyana, Lesotho

Abstract Conflicting reports appear in the literature from geomorphic studies describing the colder Late Pleistocene environmental conditions of the Lesotho Highlands in southern Africa. Evidence is given for limited glaciation and/or periglacial conditions, with or without permafrost. An investigation of the distribution, morphometric attributes and surface weathering characteristics of relict openwork block accumulations in the area around Thabana‐Ntlenyana, the highest summit in the range, supports the contention for a relatively arid periglacial environment during the Last Glacial period. A phase of enhanced block production is evident from the concentration of blocks in the upper layer of colluvium. Slope mobility on south‐facing slopes is shown in the blockfield fabrics and the increase in downslope relative age of block surfaces. Block production and slope creep are attributed to depressed temperature conditions and seasonal freeze. Colluvium, within which blocks have been incorporated and superimposed, indicates that slope mantles predate the onset of the colder period and evidence militates against either deep snow cover or localised glaciation of south‐facing slopes.

ROCK WEATHERING CHARACTERISTICS AS RELATIVE-AGE INDICATORS FOR GLACIAL AND POST-GLACIAL LANDFORMS ON MARION ISLAND

ABSTRACT Rock weathering characteristics as relative-age indicators are tested on rock surfaces of generally known chronological sequence on Marion Island in the sub-Antarctic. Relict Late Pleistocene glacial bedrock surfaces and glacial deposit rock surfaces provide both Schmidt hammer rebound values and weathering rind thickness indicative of the longest exposure to weathering. While the weathering characteristics could not establish any chronosequence in the relict glacial rock surfaces the techniques can resolve relative ages in the primarily Holocene post-glacial rock surfaces. An assessment of clast angularity as a relative-age indicator proved less effective but confirmed the general trend portrayed by the other two techniques.

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

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 actively accumulating ramparts, are proposed that assists in discriminating relict and active pronival ramparts from other discrete bedrock cliff‐foot debris accumulations.