SEDIMENTARY PROCESSES/Glaciers 663 Lewin J (1989) Floods in fluvial geomorphology In: Bevan KJ and Carling PA (eds.) Floods: Hydrological, Sedi mentological and Geomorphological Implications, pp 265 284 Chichester: Wiley Lewin J and Brewer PA (2002) Laboratory simulation of clast abrasion Earth Surface Processes and Landforms 27: 145 164 Meybeck M (1976) Total mineral dissolved transport by world major rivers Hydrological Sciences Bulletin, International Association of Scientific Hydrology 21: 265 284 Milliman JD and Meade RH (1983) World wide delivery of sediment to the oceans Journal of Geology 91: 21 Nanson GC and Croke JC (1992) A genetic classification of floodplains Geomorphology 4: 459 486 Nanson GC and Knighton AD (1996) Anabranching rivers: their cause, character and classification Earth Surface Processes and Landforms 21: 217 239 Petts GE, Moă ller H, and Roux AL (eds.) (1989) Historical Change of Large Alluvial Rivers: Western Europe Chichester: Wiley Schumm SA (1977) The Fluvial System New York: Wiley Thorne CR, Hey RD, and Newson MD (eds.) (1997) Ap plied Fluvial Geomorphology for River Engineering and Management Chichester: Wiley Willgoose GR, Bras RL, and Rodriguez Iturbe I (1991) Results from a new model of river basin evolution Earth Surface Processes and Landforms 16: 237 254 Williams GP (1983) Palaeohydrological methods and some examples from Swedish fluvial environments Geografiska Annaler 65A: 227 244 Glaciers M J Hambrey and N F Glasser, University of Wales, Aberystwyth, UK ß 2005, Elsevier Ltd All Rights Reserved Introduction Glaciers are amongst the most powerful geological agents on the Earth’s surface They are not only responsible for carving out some of the world’s finest landscapes, but also have left widespread deposits that influence agriculture and groundwater flow and provide abundant reserves of sand and gravel for the construction industry At present, approximately 10% of the Earth’s land surface is covered by glacier ice, whilst during Pleistocene glaciations the figure was at least 30% Continental-scale glaciations occurred in Permo-Carboniferous, Ordovician–Silurian, Neoproterozoic, and Palaeoproterozoic times The greatest of these glaciations was during the Neoproterozoic, and this has given rise to the concept of the ‘snowball Earth’, with some geologists arguing for a near-total freeze-up of the planet, followed by severe greenhouse warming, which might have triggered the explosion of life When the idea of a great Ice Age was first mooted by the Swiss natural historian Louis Agassiz in 1837 (see Famous Geologists: Agassiz) it met with fierce opposition In the following decades, increasing numbers of geologists were won over to the concept, as the evidence for glaciation, in the form of characteristic landscapes and extensive surficial deposits (‘drift’), throughout Europe and North America became irrefutable Towards the latter part of the nineteenth century, glacial deposits were being discovered in rocks as old as the Precambrian, although the validity of a glacial interpretation of rocks of Neoproterozoic age was challenged by many until as recently as the 1970s It was only after glaciologists began examining the processes of erosion and deposition in modern glaciers, from the late 1960s onwards, that the older records of glaciation could be evaluated systematically Global Distribution of Glaciers The global extent of glacier ice has been documented by the World Glacier Monitoring Service (Table 1) The two largest ice-masses, Greenland (10.9%) and Antarctica (85.7%), account for the bulk of glacier ice on Earth, although it is the remaining 3.4% that impinges directly on human activity (Figure 1) The remaining ice-masses occur throughout the Arctic islands and on high mountains, even in the tropics It is the major ice-masses that are most likely to Table Distribution of glaciated areas of the world (data from the World Glacier Monitoring Service, 1989) Region Area (km 2) Africa Antarctica Asia and Eastern Europe Australasia (i.e New Zealand) Europe (Western) Greenland North America excluding Greenland South America 10 13 593 310 185 211 860 53 967 726 400 276 100 25 908 World total 15 861 766