GLACIERS AND ENVIRONMENTL CHANGE PART III

Holocene Glacier and Climate Variations

Canada

The little Ice age was the most extensive Neoglacial glacier Advance in the Canadian Rocky mountains. Evidence of Earlier, less extensive Neoglacial advances is based on wood recovered from several glacier forefields. Three Radiocarbon dates, ranging between 8230 and 7550 yr BP obtained from wood flushed out of Athabasca Glacier and two dates from Dome Glacier Ranging between 6380 and 6120 yr BP indicate that the forests occurred upvalley of present glacier fronts due to the hysithermal. Radiocarbon dates from detrital and in situ logs indicate the forests were overridden by glaciers between 3100 and 2500 yr BP. This advance termed the Peyto Advance did not extend beyond little Ice Age maximum position. The earliest Little Ice Age advance is dated to ca 900-600 yr BP. Prior to the deposition of the Mazama Tephra 6800 yr BP, a minor glacier readvance (the crowfoot Advance) left deposits in the Rockied and the Interior of British Columbia (Osborn and Luckman 1988). The first Neoglacial Advances took Place 6000 – 5000 yr BP. Other Advances occurred between 4000-3000 yr BP and at About 2500 and 1800 yr Bp. The little Ice Age expansion which started shortly after 900 yr BP, culminated in the eighteenth and nineteenth centuries.

USA

In the American cordillera, a late glacial or early Holocene glacier readvances or stillstand deposited moraines about 1-3 km beyond present glacier fronts. The earliest dated neoglacial advance occure at about 5000 yr BP. In most mountain ranges of the western USA, unweathered sharp crested moraines adjacenet to modern ice margins or near cirque headwalls without glaciers at present date to the little Ice Age of the last several centuries.

The Alps

Cores removed from proglacial Lake Silvaplana in the swiss Alps showed that Glacial varves were deposited during glacil retreat in the early Holocene until 9400 yr BP. Glacial activity was absent of negligible within the catchment between 9400 and 3300 yr Bp. Maximum varve thickness, interpretated as reflecting the size of the glaciers in the catchment was observed between AD 1790 and 1870.

	9400 -9000 yr BP	9000 – 6000 yr BP	6600 -6000 yr BP	7700 – 7300 yr BP	8400 – 8100 yr BP	6000 – 4600 yr BP	4600 – 4200 yr BP	4600 – 3600 yr BP	#600 – 3000 yr BP
Advance	O		O	O	O		O		O
Retreat		O				O		O

Tree trunks and wood fragments in minerotrophic accumulated in the outwash plain of Unteraargletscher, Switzerland have been radio-carbon dated to represent Holocene retreat phases of the glacier.

Little Ice Age Glacier Variations

The Alps

The most recent interval of glacier advance occurred in the six centuries between about AD 1250/1300 and Ad 1850/1860 during which some outlet glaciers extended 2-2.5 km beyond their present marginal positions. From the records of glacier front variations, mass-balance reconstructions, temperature and precipitation data Kuhn concluded that Glacier activity since 1860 has been generally homogenous in the Als. There was a short period at the end of the nineteenth century when regional variability of precipitation may have caused different accumulation. During the last two decades of that century, glaciers had reached nearly equilibrium size after a rapid decrease following their mid century maxima. After the 1920 advance period, Alpine Glacier were not as close to equilibrium as before and during the period 1965 to 1985. In 1930-64 period was characterized by high continentalily, strong retreat and rather uniform response to the alpine glaciers.

The climate in the European Alps during the 20^th Century has been characterized by an increase in minimum temperatues of approximately 2C, a smaller increase in maximum temperatures and a decrease in sunshine during the mid 1980s. the temperature increase was most pronounced in 1940s and 1980s. Since the id 1850s (peak of little ice Age), the glaciated area has been reduced by 30-40 percent and by about half of the glacier volumn.

Switzerland

There is strong evidence of advancing glaciers before the sixteenth century from the eastern part of Valais and from the Bernese Oberland. Tree Logs from Within and soils from beneath, moraine sequences have been radio-carbon dated, majority of them giving dates ranging from the 8^th to 10^th century. The glacier fluctuations of the Unterer Grindelwaldgletscher was most extensive between 1600 and 1870. It reached its maximum extent between 1590 and 1640.

SOME DIAGRAM RELATED TO GLACIAL MAPPING