8324-1 to 3 Bogong High Plains

This information has been developed from the publications:

Sites of Geological and Geomorphological Significance in Central Gippsland (1981) by Neville Rosengren, M.S McRae-Williams and S.M Kraemers.
Sites of Geological and Geomorphological Significance in the Gippsland Lakes Catchment (1984) by Neville Rosengren.
Sites of Geological and Geomorphological Significance in East Gippsland, Victoria (1981) by Neville Rosengren, M.S McRae-Williams

Geological heritage sites, including sites of geomorphological interest and volcanic heritage sites, are under regular revision by the Geological Society of Australia, especially in the assessment of significance and values. Reference should be made to the most recent reports. See the Earth Science Heritage section of the Geological Society of Australia website for details of geological heritage reports, and a bibliography.

Introduction:

The Bogong High Plains, are located at an altitude of between 1600 and 1800 metres and are characterised by a gently undulating topography drained by a series of broad alluviated valleys. The plains are in marked contrast with the surrounding deeply dissected terrain. The High Plains extend from the Mount Jim-Mount Cope area in the south to the Spion Kopje-Mount Nelse ridge. The planar areas north of Mount Nelse are essentially flattened or gently sloping spur tops separated from the similar alpine environment of Mount Bogong by the Big River valley.

The High Plains represent a remnant of an older land surface, which has been preserved by faulting along the Tawonga Fault and other parallel faults, and by regional warping. Fault warping has exerted a considerable influence on the drainage pattern of the High Plain and thus indicates that the faults have been active in late Tertiary times.

The dominant rock types of the Bogong High Plains are schists and gneisses which weather easily and upon which a deep cover of regolith has often developed. Exposures of these metamorphic rocks are generally poor with outcrops occurring only on the steep exposed slopes of the mountain summits, and in the steep valley and gorge sections associated with the rejuvenated streams draining the high plain area. Much of the topography of the High Plains is due to basalt flows, which are relatively resistant to erosion and have remained as capping residuals, forming plateau- like summits. The basalt is interbedded with tuffs and sediments, differential erosion of the softer materials has resulted in the formation of a stepped topography in several area.

On the basis of Pleistocene glaciation features in the Mount Kosciusko area, it has been argued that glacial landforms would be expected at similar elevations in the Victorian Alps. However, unequivocal evidence of glaciation in lacking in the Bogong High Plains area and it appears that periglacial, rather than glacial, processes have been a major factor in determining the landforms of the Bogong High Plains. Several areas show landforms related to past down slope movement (solifluction lobes and stone stripe patterns) under permafrost conditions.

Evidence of periglaciation is found in the soils of the High Plains. The dominant soil type- alpine humus soils- is often of considerable depth and has developed not only on bedrock, but also within regolith, which shows evidence of earlier down slope movement and mixing. Deep lithosols are invariably relict soils. The importance of periglacial weathering processes is that subsequent soil formation and plant succession can be very rapid. The risk of accelerated erosion on de-vegetated soils is unusually high and the stability of landforms and soils on the High Plains is therefore dependent on the maintenance of vegetation cover. Once exposed, the light friable alpine soils are subject to the action of needle-ice, hight-intensity rainfall and high-velocity winds resulting in increased surface soil instability, sheet erosion and limited gullying of surficial soil layers.

The maintenance of many of the features of geomorphological significance on the Bogong High Plains is in part dependent on the retention of the vegetation cover- particularly on the treeless alpine zone. Accelerated erosion, including gullying and sheet wash that follows extensive disturbance to the vegetation, can obscure many of the small-scale periglacial features. The periglacial features, eg. Solifluction lobes, are relict features from colder climatic phases in the Pleistocene and hence will not be rapidly reformed if they are obscured by rapid slope movements. Similarly, the bog peats are sensitive to damage and many have probably been degraded in the past 100 years. The bogs occur only in permanently wet situations. Alterations of their naturally diffuse drainage system to a channelled drainage pattern either through trampling or erosion by gully formation rapidly degrades these features.

The sensitivity of the High Plains to overuse is widely recognised and recorded. Conspicuous examples exist in many areas of the impact of man and his introduced herbivores upon the alpine environment. These include the drainage of peat bogs and their damage via trampling by livestock and pedestrians, ski-resort development, compaction and/or erosion of soils on tracks by walkers and off-road vehicles and the grazing and trampling of alpine meadows. The use of these areas requires a detailed investigation of their use/ effect/ benefit relationships and the subsequent formulation of specific management prescriptions, which would preserve the environmental quality, and diversity of the High Plains.

Note: Grid reference for the following sites have been based upon a pre-publication dyeline copy of the Bogong (8324) Map sheet, and may be subject to minor mirror. The sites as defined, cover relatively large areas and the grid references indicate general site boundaries only.

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