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The Last Glacial Maximum (LGM) is widely used to refer to the episode when global ice volume last reached its maximum and associated sea levels were at their lowest. However, the boundaries of the interval are ill-defined and the term and acronym have no formal stratigraphical basis. This is despite a previous proposal to define it as a chronozone in the marine records on the basis of oxygen isotopes and sea levels, spanning the interval 23–19 or 24–18 ka and centred on 21 ka. In terrestrial records the LGM is poorly represented since many sequences show a diachronous response to global climate changes during the last glacial cycle. For example, glaciers and ice sheets reached their maximum extents at widely differing times in different places. In fact, most terrestrial records display spatial variation in response to global climate fluctuations, and changes recorded on land are often diachronous, asynchronous or both, leading to difficulties in global correlation. However, variations in the global hydrological system during glacial cycles are recorded by atmospheric dust flux and this provides a signal of terrestrial changes. Whilst regional dust accumulation is recorded in loess deposits, global dust flux is best recorded in high-resolution polar ice-core records, providing an opportunity to define the LGM on land and establish a clear stratigraphical basis for its definition. On this basis, one option is to define the global LGM as an event between the top (end) of Greenland Interstadial 3 and the base (onset) of Greenland Interstadial 2, spanning the interval 27.540–23.340 ka (Greenland Stadial 3). This corresponds closely to the peak dust concentration in both the Greenland and Antarctic ice cores and to records of the global sea-level minima. This suggests that this definition includes not just the coldest and driest part of the last glacial cycle but also the peak in global ice volume. The later part of the LGM event is marked by Heinrich Event 2, which reflects the onset of the collapse of the Laurentide at c. 24 ka, together with other ice sheets in the North Atlantic region. A longer and later span for the LGM may be desirable, although defining this in chronostratigraphical terms is problematic. Whichever formal definition is chosen, this requires the contribution of the wider Quaternary community. [ABSTRACT FROM AUTHOR]

In conjunction with detailed geological mapping around the Aim and Straneggtal, in Upper Austria, the landslide deposits have been restudied. Along the southern flank of Meisenberg, coarse angular debris with boulders up to ca. 5m3 size occur. These are composed only of bright Dachsteinkalk sitting as erratic material on the dark-grey limestone of the Gutenstein Formation. The coarse grain size and its distribution only above the trim line of the Last Glacial Maximum (LGM) indicates that this material was deposited in a large-scale rock avalanche. This was derived from the northern rim of the Totes Gebirge and travelled north, spreading out over the glacier and finally reaching the flank of the Meisenberg, some 6km away. Similar deposits at Jh. Miraberg are also remnants of this debris blanket, deposited when the glacier finally malted away. The Hintere Hetzau cirque and the Staneggtal show a conspicuously hummocky topography, covered with huge blocks of Dachsteinkalk. The hummocks consist of densely packed matrix-supported angular debris of Dachsteinkalk and Hauptdolomit, deposited by a huge landslide (ca. 450 million ms. This was derived from the Büchsenkar and formed a sturzstrom filling the whole Straneggtal. The conspicuous ridges north and south of Drackhütte are surge ridges (Fleckberg) and wave-like ridges created by the dynamics of the sturzstrom. On reaching the Almtal, the sturtzstrom probably entered a shallow lake and was transformed into a suspension that was pushed forward by subsequent incoming material. This suspension flow created a terrace body as far north as the Grünau basin. Sedimentary structures indicate that this occurred in a single short event. Lumps of still dry and densely packed landslide material floated in and above the suspension, forming small hills on the surface of the terrace. Larger lumps of still stratified sandy-gravelly river sediments indicate transport in a frozen state indicating wintertime or early spring conditions. 36Cl surface exposure dating indicates that the avalanches occurred at the end of the LGM, probably shortly before the glaciers started their final melting. The boulders at Meisenberg were deposited around 19,000 years ago. The younger main event, at Straneggtal, took place at the end of the Oldest Dryas, after melting of the Gschnitz stadial glaciers; the most representative age of boulder deposition is 15,600 ± 1100 years. [ABSTRACT FROM AUTHOR]

During the Last Glacial Maximum (LGM), a 5000 km2 ice cap covered the San Juan Mountains of southwest Colorado. The largest valley glacier draining this ice cap occupied the Animas Valley and fl owed 91 km to the south. To characterize the post-LGM demise of the Animas Valley glacier, we employ cosmogenic 10Be to date the LGM terrace outside the terminal moraines and a suite of seven glacially polished bedrock samples. The 10Be depth profile within the terrace sediments suggests abandonment at 19.4 ± 1.5 ka. As deglaciation began, the ponding of Glacial Lake Durango behind the terminal moraines shut off fluvial sediment supply and caused terrace abandonment. The age of the terrace therefore records the initiation of LGM retreat. Negligible 10Be inheritance in the terrace profile suggests that glacial erosion of the bedrock valley floor from which sediments were derived erased all cosmogenic inventory. Glacial polish exposure ages monotonically decrease up-valley from 17.1 to 12.3 ka, with the single exception of a sample collected from a quartzite rib, yielding an average retreat rate of 15.4 m/yr. This trend and the lack of inherited cosmogenic nuclides in the terrace sediments imply that polish ages accurately record the glacial retreat history. Retreat of the Animas lobe began at a time of regional drying recorded in sediments and shoreline elevations of large lakes. Deglaciation lasted for ∼7.2 k.y., and was complete by 12.3 ± 1.0 ka. The retreat history followed the pattern of increasing insolation and was perhaps fastest during a time of regional drying. [ABSTRACT FROM AUTHOR]

Theories that propose feedbacks among climate, tectonics, and surface processes commonly assume that erosion is enhanced by glacial activity. Indeed, studies have shown that glaciers appear to limit the elevation of mountain ranges; however, comparisons between rates of glacial and nonglacial erosion are difficult to make. Ideally, such comparisons must hold precipitation and lithology constant, while only varying the erosional regime. Located in a climatic transition zone during the Pleistocene, the east-west-trending valleys of the Bitterroot Range present an opportunity for a quantitative analysis of glacial and nonglacial erosion because the north-facing sides of the valleys were glaciated, whereas the south-facing slopes were not. The different erosional regimes operating on either side of the valleys created strongly asymmetric ridges. Ridgelines separating the east-west-trending valleys have been pushed southward by glacial headwall retreat such that ridge-to-valley distances are ∼50% greater on the north-facing slopes than on the south-facing slopes. In addition, mean hillslope angles are 6° lower on the glaciated slopes than on the unglaciated slopes, and calculations of geophysical relief suggest that, on average, glaciers have removed nearly twice as much rock as nonglacial processes. Finally, we conclude that, although rates of vertical incision by glacial processes in the Bitterroot Range were more rapid than nonglacial processes, the dominant geomorphological impact of glaciers was lateral erosion by headwall retreat. [ABSTRACT FROM AUTHOR]

Seismic hazard evaluations on major faults in Earth's crust are based on their slip histories, which reflect the frequency of earthquakes that ruptured a fault in the past. On a 100 000-year timescale, the slip rate of a fault can be determined by dating geomorphic surfaces that are offset by a fault. Application of this method to alluvial fan surfaces and river terraces offset by thrust faults in Tibet yields long-term slip rates of less than 1mm/a. Slip rates on a 10 000-year timescale are derived from paleoseismologic data and document that faults experience considerable slip rate variations on timescales of 100 to 1000 years. In particular, slip rates are often considerable higher in the present interglacial, the Holocene, than during the last glacial period, the Late Pleistocene. The causes of this behavior have remained enigmatic but their assessment is essential for an accurate evaluation of a fault's past and future seismicity. Numerical experiments show that the retreat of lakes and glaciers at the end of the last glacial period can cause an increase in the Holocene slip rate of a fault. Such a correlation between enhanced seismicity and climate-driven mass fluctuations on Earth's surface is best documented for the Wasatch Fault, Utah. [ABSTRACT FROM AUTHOR]