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This article discusses the plan and profile morphology, characteristics, composition, and origin of talus (scree) slopes and describes the main formative processes (including rock fall, talus creep, and grain flows). It also briefly illustrates the modification of talus by snow avalanches and debris flows. Finally, it discusses in brief the rate of formation of talus, their possible paraglacial origin in some cases, and paleoenvironmental interpretation of talus deposits.

Rockfall is defined as the free or bounding downslope movement of loose rock material under the influence of gravity. Studies of rockfall are most commonly carried out in mountain areas and associated with debris delivery from high cliffs to the talus (or scree) landforms that accumulate at the base of the cliff. Talus slopes are significant and commonly well-preserved elements of many mountain landscapes. The main triggers of rockfall activity are freeze–thaw or frost-cracking processes (segregation ice growth) on the cliff, extreme precipitation events moving loose debris downslope, earthquakes, and possibly pressure release following deglaciation of rock walls. The main process studies have involved inventory of events by direct observation or records of damage; measurement of accumulation rates on marked surfaces or transportation links; or by the calculation of volumetric estimates of talus accumulation over long timeperiods. There has also been considerable study and modeling of rockfalls as an engineering hazard to infrastructure (roads, railways and buildings in mountain areas) has also been done, including estimates of rockfall magnitude and frequency from tree-ring records. A few process studies have also examined rockfalls from eroding coastal cliffs in bedrock.

The plan and profile morphology, characteristics, composition, and origin of talus (scree) slopes are discussed with a description of the main formative processes (rockfall, talus creep, grain flows, etc.). Modification of talus by snow avalanches and debris flow is also briefly illustrated. Finally there is a short discussion of the rate of formation of talus, their possible paraglacial origin in some cases, and paleoenvironmental interpretation of talus deposits.

Pollen, macrofossils and isotopic data ( 13 C, 18 O) from gastropod shells are used to reconstruct Holocene vegetational and climatic changes for a lower subalpine forest site (elevation 1690 m) in the Maligne Valley, Jasper National Park, Alberta. Subalpine forest has characterized the site since the inception of the sedimentary record in this small pond ca. 8500 yr B.P. In contrast to the vertical timberline fluctuations recorded at nearby sites above present tree-line, vegetational changes at the site appear to have been mainly horizontal, i.e. forest cover and tree density expanded or contracted laterally in response to climatic warming or cooling. At Maligne Lake forest cover was probably at its maximum extent about 7500 yr B.P., when Pseudotsuga and other montane elements had migrated to this elevation but did not displace the existing vegetation. The modern mosaic of discontinuous subalpine forest and extensive dwarf birch-dominated damp meadows and fens emerged only during the last 1300 years. A warmer Neoglacial episode, dated ca. 2600–3400 yr B.P., is indicated by increases in the temperature-limited gastropod, Lymnaea palustris , and by progressive enrichment in the 18 O and 13 C contents of their shells. Summer temperatures during this period, which has been tentatively identified elsewhere in the Canadian Rockies, may have risen by as much as 1.8°C.

Dirty snow avalanches have been observed to carry considerable amounts of rock debris on to lake ice at the foot of scree slopes. As ice breaks up in the spring thaw, this material is carried back and forth on ice floes and is gradually deposited in the lake. In some areas this produces typical drop stones of rock debris in predominantly fine-grained deposits. Most avalanche debris is very angular which enables avalanche drop stones to be differentiated from those of glacial or other drift-ice origins. However, where avalanches incorporate glacial debris, such deposits may be indistinguishable from those formed by floating glacier ice.