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Glacial History: During the past two million years there have been five major glacial advances and five glacial retreats, the last of these being our present period, the Holocene [1].
Large ice sheets covered the northern continents: most of the British Isles, the North Sea, The Netherlands, northern Germany and Russia were part of an ice sheet centred on Scandinavia and the Baltic, while mountain glaciers descended from the Alps and the Pyrenees.
Vegetation and Wildlife. The vegetation zones of the park are sharply defined, and their distribution is closely correlated with both the glacial history of the region and the altitudinal variation of the monutains. Meltwaters of receding glaciers of the past carried away the finer soils of the valley floor, leaving extensive outwash plains of porous cobblestones. On these broad plains drought-resistant sagebrush is the dominant plant.
The chronology of the periods of glacial advance and retreat is established by the study of periglacial lake sediments (forming annual layers known as varves), of fossil pollens of plants (showing the climatic conditions), of fossil soils between two glacial layers, and of ancient beaches and river terraces which reflect former sea-levels. Other dating techniques involve radio-isotopes and tree rings, while micro-fossils in deep-sea sediments and oxygen isotopic ratios from marine fossils provide clues to the then prevailing temperatures. |
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