GLACIAL AND PERIGLACIAL

GLACIAL AND PERIGLACIAL FEATURES

Late 20th century retreat
- Alpine Glaciers
- Greenland Ice Sheet

CIRQUES and MORAINES form at 0^oC - -6^oC mean summer temperature if moisture sufficient

Cirque: glacial bowl formed in mountains , position strongly effected by winter wind (snow drift). Baffin Island	Wheeler Peak, NV	Pinedale Moraine, Wyo.
Moraine: glacially-transported material deposited at side or end of glacier. "Full Glacial" Angle Lake moraines and Pre-full glacial Lammoile moraines

Climate Reconstruction based on modern lapse rates

-6^oC/1000 m mean annual temperature
+50 cm/1000 m mean annual precipitation

Modern Snow lines (Equilibrium Line Altitudes = ELA's) are compared with Glacial age elevations of cirques and moraines

winter accumulation
summer ablation (Locke, 1989)
wind flow
cirque orientation
backwall height

Last Glacial Maximum ELA's were 1000 m lower
no Pleistocene snow lines at 30^o N because mountains too low

Pattern of LGM lowering generally parallels modern patterns so atmospheric circulation patterns similar to those of today. (Zielinski and McCoy, 1987)
Tropical cirques in Hawaii and Andes were 800 - 1000 m loweer
Pattern of coastal - inland increase is the same (Leonard, 1984; Dohrenwend, 1984)
Rainshadow Effect same as today
LGM and modern both higher in the lee of the Sierras, and near 30^o

Climatic Interpretation of ELA Lowering

Many possible combinations of precipitation and temperature may have produced Glacial Pattern in Colorado Rockies (54% increased winter accumulation; Leonard, 1989)
NOT 6^oC colder AND 50 cm/yr more precipitation
- Same Precipitation and 8.5^oC colder = 54% increased winter accumulation
  OR
- 75% reduction of temperature and 13^oC lowering = 54% increase

PERIGLACIAL FEATURES:

patterns in soil and surface deposits resulting from permafrost

Modern Tibetan Plateau (INQUA International Symposium 1998)

During the last glaciation, patterned ground was much more extensive, and ca. 1000 m lower than today

J. Steven Kite
- patterned ground: polygons of various sizes (2), with sediment of different texture or color filling old cracks
- ice wedges: V-shaped infillings which form in very cold (<-18^oC) areas in winter, with little snow cover (cold-dry)
- stone polygons: patterned ground with rocks making the pattern
- stone stripes: (patterned ground) elongated ridges formed from rocks

LATE HOLOCENE GLACIAL ADVANCE & RETREAT

e.g., Quelccaya Ice Cap, Peru. 163.6 m thick, 1500 years old. (5670 m, -3^oC) has now melted

ablation (sublimation) during dry period
thinner glaciers = less precipitation on summits
pattern and timing of retreat very similar to global warming
- Historic Retreat
- Little Ice AgeLittle Ice Age A.D. 1300-1910
  
  events
  A.D. Wolf
  1330 Sporer
  1550 Maunder
  1710 Dalton
  1825
  
  ELA's in the N. hemisphere were ca. 100 - 200 m lower (Porter, 1986)
  - MORE extensive than early Holocene in Canadian Rockies (Osborn & Luckman, 1988)
  - LESS extensive than early Holocene in Great Basin (Osborn & Bevis, 2001)
    - 1- 3 ^o C colder δ ¹⁸O/¹⁶O
    - 5 - 10 cm more annual precipitation
- Medieval Warm Period A.D. 1050-1250
  - Tree lines 100-140 m higher in Fennoscandia (Russia) ca. AD 1000-1300 (Boettger and Kremenetski, 2001)

Neoglacial (the last ca. 3500 years)

snow lines were lowest 2600 - 2800 yr B.P. in Rocky Mountains
Neoglacial lowering LESS than LIA in the Canadian Rockies and the Sierras.
Earlier Holocene advances indicate a 2500 yr climatic cycle. (Denton & Karlen, 1973).

GLACIAL ADVANCES AS CAUSES OF CLIMATE:

Younger Dryas (11-10K) surge of sea ice from Arctic and Norwegian Seas (Ruddiman & Glover, 1975)
1. increased albedo and lowered temperatures in North Atlantic
2. stratification (reduced salinity) and less evaporation

Periglacial Readings

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