Typically such deposits, where unconfined, are sheetlike or tonguelike. The long dimension may exceed 15 km (Watson and Wright, 1969) and units may be from a few meters to several hundred meters thick. Volcanic debris-avalanche deposits may be even larger, and extend for over 100 km where constrained in valleys, and cover areas exceeding 2000 km2 (Siebert, 1984; Stoopes and Sheridan, 1992).
As most descriptions of landslide deposits are of undissected Quaternary units, few descriptions contain detailed quantitative information on internal grading and or sorting. Most units appear to be non-graded. However, Cruden and Hungr (1986), showed a single section through the Frank slide in Alberta to be reversely graded. Krieger (1977) also refers to a general coarsening upward in both the Escabrosa and lower Martin megabreccias. Notwithstanding the apparently chaotic nature of most avalanche deposits, the relative position of the source lithologies may be preserved during transport in large volume deposits, generating a "ghost stratigraphy." This is the case in the Blackhawk slide (Shreve, 1968) even though material was transported for distances of up to 8 km. In the even larger Saidmerreh slide deposit, blocks of Asmari Limestone are prominent in the upper part of the deposit above Eocene debris, reflecting the original stratigraphic relations (Watson and Wright, 1969).
Deposits of this type invariably contain angular to subangular fragments, although clast roundness may vary with the lithology or clast size. Clast composition is largely a function of the nature of the rocks in the source area. The amount of foreign material entrained during transport is typically minimal. As a result, deposits derived from large, uniform rock masses such as granites and serpentinite bodies are often mono-lithologic. Material within large-volume deposits is normally intensely fractured, with the development of "jigsaw" or "crackle" textures. Mudge (1965) noted that even relatively small units may show clast fracturing. Shreve (1968), describing blocks from the Blackhawk slide, noted that some were severely shattered, but that the constituent fragments were displaced only by a few centimeters. Clast size is highly variable, but very large clasts, greater than 100m in diameter, may be preserved (Watson and Wright, 1969).
The matrix typically results from the cataclastic fragmentation of the source rocks and may make up 90% of the deposit. Little quantitative information on the matrix grain size characteristics is available, but coarse- to medium-grained sand-size material is common.
Yarnold (1993) notes that giant landslide deposits "commonly contain discrete internal slip surfaces" marked by deformation and shear along zones of the order of 100 mm thick. These zones are common in the lower Martin megabreccia (Krieger, 1977) and appear to represent zones of considerable movement within the slide. The base of such deposits may be associated with considerable disturbances of the underlying rocks if the latter were unconsolidated at the time of the emplacement of the slide deposit. This deformation may take the form of scouring and "bulldozing." In large deposits, flowing over poorly consolidated sediments, this deformation may extend to a depth of 5 m. Krieger (1977) notes that the distal end of the El Capitan landslide "plowed into the underlying sediments, compressing them into folds." Much attention has been paid to minor topographic features on the upper surface of giant landslide deposits. However, it is probably sufficient to note here that such upper surfaces are typically highly irregular, hummocky, or ridged.