| INTRODUCTION TO ICE AGES James S. Aber |
| Environmental basis | History of development |
| Quaternary Period | Modern glacial theory |
| Related sites | References |
Evidence from glacier ice, or left by glaciers in the landscape or
within the geological record, provides one of the most important
sources of information on environmental change.
(Nesje and Dahl 2000)
The Earth is not an isolated, closed system; it is an evolving planetary body that is much influenced by extra-terrestrial as well as internal events and forces. Within the solar system, the Earth is unique; it has a lithosphere, hydrosphere, cryosphere (frozen portions), atmosphere, and biosphere (Verdon 1988). The interaction of these material results in Earth-surface environments that are infinitely complex--see Fig. 1-1. The Earth's environment has been compared to a great symphony, in which complicated melodies, tones, and rhythms interact to produce harmony or dissonance--see Fig. 1-2. Ice ages are a theme that has occurred often in Earth history (Cloud 1988).
According to Eddy (1993), it is clear the Earth faces an environmental crisis brought about in part by human activities. Six actions seem so essential as to constitute a set of imperatives for science in the 21st century:
| Photograph of Sandfellsjökull, an outlet glacier of Mýrdalsjökull ice cap, southern Iceland. Photo date 8/94; © by J.S. Aber. |
Pálsson reached significant conclusions concerning formation and dynamics of glaciers. He recognized that glaciers move by creep in a way analogous to the flow of pitch. He dealt with glacial sediments, melt-water rivers and floods, and the effects of subglacial volcanism. Pálsson's treatise was sent to the Danish Society of Natural History in 1795, but it was forgotten at the time and not published until nearly a century later. Iceland remained a remote location for geological investigations until the 20th century.
The concept of former extension of glaciers and ice sheets began to develop in the late 18th and early 19th centuries in the Alps of central Europe and the mountains of southern Scandinavia. Many early mountaineers, naturalists, and scientists were involved, of which several played key roles. Horace-Bénédict de Saussure was among the earliest naturalists to undertake systematic observations of glaciers in the Mont Blanc vicinity beginning in the 1760s. His work culminated in Des glaciers en général, which was published in volume 1, chapter VII of his Voyages dans les Alpes (1779). In this synthesis, he reviewed types of glaciers, ice flow, origin of moraines, and many other aspects of glaciers. Saussure introduced the terms roches moutonnée, sérac, and moraine into geological usage (Carozzi and Newman 1995).
James Hutton was first to recognize in 1795 that erratic granite boulders in the Jura Mountains had been transported by glaciers from the Alps (Flint 1971). Such erratics were then commonly believed to be results of a great flood, whence the term drift was derived. This term is still in general use for any kind of glacially derived sediment.
| Aletsch Glacier, central Swiss Alps. View from near head looking down ice along glacier. This is the largest glacier in the Alps today; it extends some 20 km downvalley. Photo © by Foto Meier, Thun |
| Photograph of large erratic boulder in western Denmark. The boulder is crystalline rock transported by glaciation from the mountains of southern Norway. Scale pole marked in 20-cm intervals. The erratic block is approximately 6.5 m long. Photo date 6/79; © by J.S. Aber. |
In Scandinavia, Jens Esmark concluded in 1824 that glaciers had once been much larger and thicker, and had covered much of Norway and the adjacent sea floor (Andersen 1992). He made observations in the central mountain district as well as on coastal plains and fjords--see Fig. 1-4. He attributed erratics and moraines to glacial transportation and deposition. He also recognized that glaciers were powerful agents of erosion that had carved out the Norwegian fjords (Cunningham 1990).
| View northward along Veafjord, western Norway. City of Vaksdal to right. Fjord is some 25 km long, 2 km wide, and several 100 m deep (below sealevel). This fjord was eroded along a major fracture zone in crystalline bedrock. Photo date 5/87; © by J.S. Aber. |
| Photograph of glacial striations and grooves on Sioux Quartzite bedrock at Jeffers, Minnesota. Two directions of ice movement are indicated by crossing (x) pattern of striae. Silva compass for scale; photo date 7/96; © by J.S. Aber. |
In the early 1830s, Jean de Charpentier began to marshall the scientific evidence for former alpine glaciation. He observed moraines, striations, and erratics, as well as existing glaciers of the Swiss Alps, and presented his conclusions in a very persuasive manner (Teller 1983). His ideas initially met with much skepticism, but his work eventually became quite influential.
One of those who at first disbelieved de Charpentier was Louis Agassiz, who was already a famous zoologist. Through his own observations, Agassiz came to accept the concept of former alpine glaciation, and then carried the idea much further. In 1837 he proposed that vast sheets of ice had once covered much of the northern hemisphere. This was a radical suggestion, for at that time the modern ice sheets in Greenland and Antarctica were completely unknown.
Agassiz was a highly energetic and controversial naturalist and writer, who popularized the idea of a geologically recent ice age as the latest catastrophe in Earth history. By the mid-1800s, the glacial theory existed at three levels:
The glacial theory was initially opposed by a sizeable number of natural scientists, who prefered to interpret landscape features as the results of a great biblical flood. Some glacial deposits in former marine areas do in fact contain fossil shellfish. During the next few decades, those who opposed the glacial theory were either converted or died. The effects of glacial erosion and deposition were observed widely in Europe, the British Isles, and in North America. Charles Lyell (1863) recognized that glaciers also could deform sedimentary strata.
| Photograph of chalk-till mélange from West Runton, England. Chalk and till were sheared and mixed together by strong glacial deformation. Red pocket knife for scale. Photo date 10/88; © by J.S. Aber. |
The Norwegian Fridtjof Nansen provided final proof for the existence of ice sheets, when he crossed the southern portion of the Greenland Ice Sheet in 1888. The geography of Greenland had been the subject of several expeditions and intense debate prior to Nansen's journey. He suceeded in crossing the ice sheet, where many earlier attempts had failed, by skiing and using survival techniques of the Lapps and Eskimoes. Another Norwegian explorer, Roald Amundsen, was the first person to reach the South Pole in 1911.
By the end of the 19th century, real opposition to the glacial theory was gone, and new evidence for multiple glaciations was beginning to emerge. Both in Europe and in North America four or more glacial periods separated by interglacial episodes were identified. So the ice ages took on a cyclic character, which is still the subject of much scientific research and debate.
Lyell introduced the term Pleistocene in 1833 for deposits in which >70% of the fossil mollusca are still living species (Bowen 1978). The Pleistocene is now subdivided on the basis of paleomagnetism and oxygen-isotopes. The base or beginning of each interval is defined as follows--see Table 1-1.
The term Holocene is the newest, having been adopted in 1885 for deposits that are wholly recent in fossil content. The Pleistocene/Holocene boundary is arbitrarily defined as 10,000 radiocarbon years ago. The Pleistocene Epoch popularly represents the ice age; however, large ice masses also existed in Antarctica, Greenland, Alaska and Iceland during late Tertiary time. It is, thus, more appropriate to refer to a late Cenozoic ice age.
INQUA is the International Union for Quaternary Research, a multidisciplinary scientific organization that was founded in 1928. It is devoted to improved understanding of the Earth's environment and the processes of environmental change. All aspects of Quaternary science come under the INQUA umbrella: anthropology, archaeology, botany, climatology, geology, glaciology, oceanography, volcanology, zoology, etc. More than 5000 scientists (and science students) are involved with INQUA activities worldwide; most are associated with universities or governmental agencies. INQUA achieves its aims largely through the work of its commissions.
Similar oscillations took place for smaller ice caps and glaciers in widespread montane and maritime locations: Iceland, Alps, Yellowstone, Andes, Tibet, etc. These glacial cycles were accompanied by major changes in climate, global sea level, and shifts in plant and animal populations. Four glacial cycles were traditionally recognized in North America and Europe. These names were chosen in the late 1800s and earliest 1900s, but several are no longer accepted for stratigraphic use--see Table 1-2. * Vistulian is the English term derived from the Wisla River in northern Poland.Quaternary Period
The Quaternary Period is the last period of the geologic time scale. It follows the Tertiary Period and is divided into the Pleistocene and Holocene (Recent) Epochs--see GSA time scale. The terms Quaternary and Tertiary, although firmly established in modern usage, are archaic, dating from early geologic practice of dividing the Earth's history into four intervals. The term Quaternary was first used by Desnoyers in 1826 to describe deposits overlying Tertiary strata in the Paris basin (Bowen 1978). It was subsequently defined by Reboul in 1833 to include deposits whose fossils mainly represent extant organisms.
Based on Episodes (1988, 11, p. 228).Stage/Age Definition Beginning
Upper/Late Pleistocene oxygen-isotope stage 5/6 app. 130,000 years BP Middle Pleistocene Matuyama/Brunhes paleomagnetic reversal app. 720,000 years BP Lower/Early Pleistocene Olduvai paleomagnetic event app. 1.6 million years BP 
INQUA homepage.Modern glacial theory
Multiple glaciations by continental ice sheets during the past few million years are the basis of the modern glacial theory. Comparable glaciations also took place during certain earlier intervals of Earth history. Several major ice ages each with multiple glaciations are known in the geologic record (ages in millions of years; Harland 1983):
During each Pleistocene glaciation, large ice sheets grew in North America, Greenland and Eurasia--see Fig. 1-5. Some ice sheets were relatively stable and survived for millions of years, as in Antarctica and Greenland. Others were inherently unstable and underwent repeated growth and destruction in cyclic manner. The North American and Eurasian ice sheets have behaved this way during the past one million years with glacial cycles averaging about 100,000 years. These unstable ice sheets developed in essentially the same locations and grew to nearly the same limits during each cycle.
Central U.S.A. Northern Alps Baltic lowlands Wisconsin Würm Vistulian* Sangamon R/W Eemian Illinoian Riss Saalian Yarmouthian M/R Holsteinian Kansan Mindelian Elsterian Aftonian G/M Cromerian Nebraskan Günz Menapian
This name is often used in its German version, Weichselian.
| Reconstruction of the Wisconsin glaciation for North America and Greenland. Low sea level and exposed continental shelves are depicted along with glacial Lake Missoula and Lake Bonneville in the western United States. Image © by Jeff Silkwood, Forest Service, U.S. Dept. of Agriculture (used here by permission). Limit of glaciation taken from North American glaciotectonic database. |
| Mazurian upland, northeastern Poland. This classic glaciated landscape was molded by late Vistulian ice advances that left a beautifully undulating morainic topography. Photo date 9/93; © by J.S. Aber. |
| View over glaciated landscape, Wabaunsee County, northeastern Kansas. Erratic boulders of Sioux Quartzite (derived from SD/MN) are scattered in the foreground of this scene from the Flint Hills. The glaciation of Kansas took place more than half a million years ago. Photo date 10/89; © by J.S. Aber. |
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