ABSTRACT
The Altai Mountains in southern Russia consist of huge intermontane basins and high mountain ranges, some over 4,000 m. During the Pleistocene, the basins were filled by lakes wherever glaciers grew large enough to act as dams. Research in this remote area has revealed a fascinating geomorphic history (Rudoy 1998). The glacier-dammed lakes regularly burst out to generate glacial superfloods that have left behind exotic relief forms and deposits – giant current ripple-marks, swells and terraces, spillways, outburst and oversplash gorges, dry waterfalls, and so on. These features are ‘diluvial’ in origin, meaning they were produced by a large flood. They are allied to the Channeled Scabland features of Washington State, USA,
which were produced by catastrophic outbursts from glacial Lake Missoula. The outburst super - floods discharged at a rate in excess of 1 million cubic metres per second, flowed at dozens of metres a second, and some stood more than a 100 metres deep. The super-powerful diluvial waters changed the land surface in minutes, hours, and days. Diluvial accumulation, diluvial erosion, and diluvial evorsion were widespread. Diluvial accumulation built up ramparts and terraces (some of which were made of deposits 240 m thick), diluvial berms (large-scale counterparts of boulder-block ramparts and spits – ‘cobblestone pavements’ – on big modern rivers), and giant ripple-marks with wavelengths up to 200 m and heights up to 15 m (Plate 10.1). Some giant ripplemarks in the foothills of the Altai, between Platovo and Podgornoye, which lie 300 km from the site
of the flood outbursts, point to a mean flood velocity of 16 m/s, a flood depth of 60 m, and a discharge of no less than 600,000 m3/s. Diluvial super-erosion led to the formation of deep outburst gorges, open-valley spillways, and diluvial valleys and oversplash gorges where water could not be contained within the valley and plunged over the local watershed. Diluvial evorsion, which occurred beneath mighty waterfalls, forced out hollows in bedrock that today are dry or occupied by lakes.
