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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.

The accumulation of snow during winter and its subsequent melting during warmer months provide most of the water needed for the human populations located along the semiarid western and eastern slopes of the Andes in central Chile and central-western Argentina. The societies in these regions can be characterized as ‘hydraulic societies,’ as social tissues are strongly associated with intensive use of water resources that historically have been adapted to ‘control’ a hostile natural environment. This chapter first discusses various empirical analyses of snowpack and streamflow records that demonstrate (1) the dominant influence of snowmelt on the hydrologic regimes of the main rivers of the region, (2) the impressive similarities in these records at interannual and interdecadal timescales, and (3) the strong relationships that exist with El Nino–Southern Oscillation (ENSO) features in the tropical Pacific. The authors also use the snowpack and streamflow records available to identify the most severe dry and wet periods in this portion of the Andes over the past 100 years. Two recently developed snowpack reconstructions that extend the instrumental records for several centuries are subsequently discussed in an attempt to provide evidence that may help assess the recent patterns observed in the instrumental records in a long-term perspective. This evidence may also be used to test the time stability of the relationships with large-scale ocean–atmosphere features and to validate the results from global and local modeling exercises intended to project future hydroclimatic changes in this region. The final discussion is on the inherent vulnerabilities associated with the scarce water resources of the inhabitants of the Rio Mendoza Basin in Argentina. This exercise allows an interesting analysis to better understand the historic, current, and possibly future socioeconomic situation of the different players of this hydraulic society. Comprehensive assessments integrating results from natural and social studies are suggested as an innovative approach to anticipate future vulnerabilities to water shortages and to develop adaptation strategies toward resilience.

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 initial employment of tree rings in geomorphic studies was simply as a dating tool and rarely exploited other environmental information and records of damage contained within the tree. However, these unique, annually resolved, tree-ring records preserve valuable archives of past Earth-surface processes on timescales of decades to centuries. As many of these processes are significant natural hazards, understanding their distribution, timing, and controls provides valuable information that can assist in the prediction, mitigation, and defense against these hazards and their effects on society. This chapter provides many illustrations of these themes, demonstrating the application of tree rings to studies of snow avalanches, rockfalls, landslides, floods, earthquakes, wildfires, and several other processes. It illustrates the breadth and diverse applications of contemporary dendrogeomorphology and underlines the growing potential to expand dendrogeomorphic research, possibly leading to the establishment of a range of techniques and approaches that may become standard practice in the analysis and understanding of Earth-surface processes and related natural hazards in the future.

Ring-width chronologies have been developed for alpine larch (Larixlyallii Pari.) at six tree-line sites in the Banff–Kananaskis area of the southern Canadian Rockies. Evaluation of all chronologies confirms that alpine larch ring-width series have higher mean sensitivities, lower autocorrelation, and greater common variance than series from other tree species growing at tree line in this area. Missing and very narrow rings created cross-dating difficulties at all sites but were most problematic for the sites along the Continental Divide. Up to 1% of the rings were missing from entire chronologies, but for specific years, up to 77% of the rings were missing at one site. Marker (narrow) rings were present at all sites for the years 1610, 1654, 1715, 1720, 1723, 1752, 1799, 1824, 1842, 1844, 1915, 1925, 1951, and 1971. Tree growth rates were reduced for the periods 1675–1710, 1815–1850, and 1960–1978 whereas increased growth occurred during 1650–1680, 1750–1800, 1850–1900, and 1920–1950. The only factor that could affect all sites over such a broad geographic area is climate. Principal components analysis indicated that the first eigenvector derived from the six chronologies accounted for 70.7% of their common variance and the first three components accounted for 91.6%. The high correlation between the six first principal component and standard chronologies suggested that either method may be used for standardizing tree-ring data from alpine larch.

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.

Publisher Summary This chapter reviews glacier fluctuations of the last millennium from sites along the Pole-Equator-Pole: Paleoclimate of the America's transect. The techniques, limitations, and problems of the interpretation, and dating of glacier records are discussed. The paleoclimate signal embedded in glacier records is complex, therefore, this chapter is restricted to areas with a reasonable sample base of land-terminating glaciers that provide directly comparable, and detailed records. Particular attention is given to sites poleward of 32° C and 47° C, where dating control is better, and greater numbers of glaciers have been sampled. Regional accounts are given for the subantarctic, Patagonia, the central Andes of Chile, and Argentina, Alaska, the Canadian Rockies, and the Coast Ranges of British Columbia. The glacier record is compared with available proxy climate records, derived mainly from tree rings, to evaluate possible linkages between glacier, and climate fluctuations. There is a broad synchroneity in the initiation, and timing of Little Ice Age (LIA) glacial events along the transect. At the decadal level, there is considerable variability in both the relative extent, timing of events, and the dating of the LIA maximum position. Contrasting glacial histories can be observed even for land-based glaciers within relatively short distances, particularly in climatic transition zones. These differences also reflect the varying dominance of precipitation, temperature controls of mass balance, and non-climatic influences on glacier behavior.

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.