Chapter 20 - Holocene glacier variations in the Alps

Abstract

The Alps have perhaps the most comprehensive chronology of Holocene glacier variations in the world. Cosmogenic nuclide data have shown that in the first centuries of the Holocene, glacier frontal positions were significantly larger than Late Holocene extents. The continued cold climate from the end of the Younger Dryas on into the Early Holocene promoted periglacial activity. Rock glaciers rapidly moved into the newly ice-free terrain and exhibited sporadic activity throughout the Holocene, with rejuvenation during the neoglacial (the last ~4.2ka). The lack of preserved moraines between ~10.2 and 5.2ka provides evidence of a long-lasting glacier retreat period punctuated by a number of minor advances that probably did not exceed mid-20th century ice levels. As large glaciers did not approach nor exceed their Late Holocene frontal extents during the Mid-Holocene, precise insight into the timing of these advances is only possible from the subfossil wood record. Based on the radiocarbon- and tree-ring-dated wood material, several Holocene Thermal Maximum Phases (~10.2–4.2ka) characterised by glacier minima with smaller-than-present (CE 2000–2020) glacier extent have been recognised. From ~4.2ka—and especially from 3.6ka—the frequency and magnitude of glacier advances increased markedly. Notable maxima occurred at 3.5, 2.8–2.6, 2.1, 1.4 and 1.15ka. The ‘Little Ice Age’ (LIA), 0.74–0.14ka (CE 1260–1860)—characterised by several maxima with similar extent—is exceptionally well understood in the Alps. Prominent lateral moraines, which are a widespread feature of the high Alpine landscape and are often referred to as ‘LIA moraines’, were actually incrementally built during the neoglacial. Strong paraglacial activity linked with ongoing glacier wastage as a result of climate warming currently endangers the preservation of some of these Late Holocene landforms and the information they contain.