Glacial landforms and the
Little Ice Age
Linking process to landscape
• Glacial mechanics
grossly oversimplified
• Difficult to observe
process at base of
glacier!
• Larger system still
poorly understood
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Glacial erosion (driving forces)
• Abrasion vs. quarrying/plucking
• Ice is soft (1.5 on Mohs)
– Sediment in glacier
– Resistance of bedrock
– Force with which clasts are pressed to base
• Weight of ice (when thin)
• Drag on clasts by ice flow towards base
– Extensional flow
– Replacement of melted basal ice
Effects of abrasion
• Dependent on clast size
• Small: polish
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Striations
• Sand sized particles or sharp edges of
larger particles
• Requires sediment supply
• Discontinuous
Glacial grooves and furrows
• Big stuff- boulders
• Upper limit on size
3
Chattermarks
• Chipping/gouging/fracture of rock surface
• Ice flow “jerky”
Quarrying/plucking
• Depends principally on properties of
underlying rock
• Must be fractured
– Pressure release
– Crushing
– Freeze-thaw
– Water pressure variations
• Ice flow exerts shear on loose particles
• Ice freezes around loose particles
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Form of erosional surfaces
• Streamlined
• All bedrock, all sediment, both
• Asymmetrical forms when plucking
involved
• Jointed surface
promotes plucking
Erosional landforms
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Cirques (cwm, corrie, kar, botn)
Rock basin, often containing tarns
Oriented w/respect to radiation, winds
Elevation related to snowline
Often in headwaters of stream valleys
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Horns and arêtes
• Remnants of many cirques
Cirque erosion
• Glaciers plus mech. Weathering and mass
wasting
• Freeze-thaw at glacial base loosens particles
– Move by creep, subglacial water flow
• Ice rotates as it slides
• Headwall erosion
col
– Unloading joints (feedback)
– Aided by bergschrund
– Plucking
– Hydration shattering
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Glacial troughs
• Ice flowing beyond cirque creates glacial valley
• Differential erosion creates U-shape
– Minimum resistance to glacier flow (?)
– Form hanging valleys when trunk erodes farther
than tributaries
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Trough profile
• Variation in joint spacing?
• Preexisting irregularities, weaknesses in
valley
• Erosion increased where tributaries join
trunk
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Fiords
• Glacial trough partially submerged by sea
• Work done by submerged portion (90%) of
glacier
Deposition and depositional
landforms
• Deposited material: drift
– Nonstratified (till)
• Transported by ice
• Poor sorting
• ?Angular clasts
– Subglacial till
• Lodgement till
• Subglacial melt-out till
• Deformation till
– Supraglacial till
• Melt out (ablation)
• Flow till
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Stratified drift
• Material transported by running water
(fluvioglacial)
– More sorting, rounding
– Ice-contact deposits may be interbedded w/till
– Deposits supported by ice
– Outwash (beyond terminus)
Depositional environments
• Ice contact vs. proglacial
• Moraine
– Accumulation of ice-deposited drift
• End
– Terminal
– Recessional
• Lateral
• Interlobate
– Formed by
• Dumping, squeezing, pushing
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Stratified drift deposits
• Eskers
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Kames and kettles
• Ice-margin features
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Interior Moraine
• Ground moraine
– Low relief, hummocky
• Rogen/ribbed moraines
– Transverse ridges
• Saturated subglacial sediment
• Localized accumulation of debris at base of ice
• Debris being ploughed
• Fluted surfaces
– Longitudinal
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Outwash plains (sandur)
Climates of the last 1000 years
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Medieval warm period
900-1250 A.D. In Europe
– As warm as anything in last 8000 yrs
– Sees expansion of settlement along North
Atlantic by Norse
– Not just warmer temperatures, most
importantly lack of pack ice
• Ice inhibits sailing
• Also, ice cover prohibits fishing
• Warm temperatures allow for growth of crops not
possible from 1200-1900.
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Medieval Warm in continental
Europe
• Melting glaciers caused sea level rise
– low-lying British land becomes easily
defensible networks of islands and
channels
• Summer temperatures average 0.7-1.4
degrees higher than normal.
– Vineyards planted 300 to 500 km north
• Populations rose sharply
• Marginal lands exploited
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Time of bountiful harvests,
abundant resources
• Surge in cathedral building across Europe
• Trade routes open between Germany and
Italy as snowbound passes open
• Glacial retreats across the Alps
What happens in Europe?
• Early 13th century
– Climatic instability begins
• Glacial advances destroy irrigation canals
• Early frosts and crop failures in Poland and Russia
– people “sell their children and eat pine bark”
• Mid-late 13th century
– Similar to “medieval warm phase”
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Europe in the 14th century
• Heavy rains, extensive flooding common in
early 1300s
• Soil erosion, loss of fertility in waterlogged soil
Æ crop failures
• 1315: hunger across N. Europe
• The “Great Famine” (1315-1321)
• Population growth w/out economic growth
during last few centuries makes for unstable
situation
– End 11th century: 6.2 million in France
– beginning of 14th: 17.6 million
What happened to the Vikings?
• West Greenland settlement abandoned by
1340
• East settlement last visited 1410,
abandoned by ca. 1500
• Stock rearing became unreliable, crops
failed and the settlements were cut off
from the outside world by sea ice for
several years at a time
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14th-15th century Europe:
• Famine, plague (~1347-1351), war had
decimated populations
– 3000 villages in France abandoned
• Still lousy conditions with frequent food
shortages until ~1450, when conditions
seem to have improved
• ~1 century of relatively decent conditions
16th century-it gets bad.
• Only when summer temperatures dropped
(~1560), glaciers began to advance
• Bad storms August 3, 1562, thunderstorm in
Central Europe
– destroyed rooves, windows, hailstorm flattened
crops, stripped trees of their vegetation
– No one could remember a storm like it
– “Unnatural”; “Judgement Day”
• sign from God, work of the Devil, witchcraft
• Wine production drops simultaneously over
broad region 1580-1600 (beer)
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Emergence of witchcraft as crime
• 14th century (?), religious councils said people
couldn’t affect the weather
• When focus shifted from disease to famine, (late
14th century) magic weathermaking begins
showing up as charges in trials
• 15th century: Church recognizes crime
• Rise of humanist thought
• Coincides with brief warm phase in LIA
• Times of witchcraft persecution seen as “dark”,
and most definitely over.
• Then climatic conditions deteriorate again.
As bad weather continues...
• In smaller political entities, witchcraft trials
begin again
– Barons made uncomfortable by riots/protests
among the peasantry
– 63 witches burned in 1 town over 1563
• Intense debate begun over whether or not
people could affect the weather
• Individual “unnatural” accidents- 1 person tried
• “Unnatural” weather (collective damage/loss:
wholesale persecution
• 1580-1620
– 1000 people burned in Vaudois region of Bern
– 2700 people in Duchy of Lorraine
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1680-1730: Coldest time
• Sea ice along the coasts of Britain and
France
• 1695: ice surrounds all of Iceland for most
of the year
• Inuit kayakers sighted off Scottish coast!
– Possibly following fish who migrated south
• Permanent snow cover on Scottish
mountains
What to do about advancing ice?
• Villagers prayed
– People marched to glaciers, erected
statues, had priests perform exorcism
– Promised no festivities, balls, or card
playing for 40 years to avoid divine wrath
• Really nothing you can do
– Glaciers had seemed stationary
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