Major Ice Ages in Earth History
Pleistocene epoch = 1.8 m.y. to 10,000 yr ago
During the Last Ice Age
• 30% of the land surface was covered by ice
(only 10% covered today)
• NY was covered by ~1 - 2 km thick ice sheet
During the Last Ice Age
Sea level was ~125 m
lower than today
During the Last Ice Age
Temperatures were ~6 C colder than present
Last
glacial
Factors that Influence Climate
• Milankovitch Cycles
planetary cycles that affect amount of incoming solar radiation
• Plate Tectonics
Continent positions - relative to latitude
- affect on ocean circulation
Mountain building - amount of mineral weathering
- affect on wind patterns
• Atmospheric Variations
• Sunspot Activity
- greenhouse gas levels
- particulate levels
(affects amount of incoming solar radiation)
• Ocean Circulation Variations
(ex., El Niño / La Niña)
“Milankovitch Cycles”
Milankovitch Cycles
OBLIQUITY
In 1920, Milutin Milankovitch (Serbian
engineer and mathematician) showed
that regular variations in shape of
Earth's orbit and orientation of its
axis create variations of solar
intensity at high latitudes: warm
summers in which glaciers retreat,
and cool summers when they
advance. These climate cycles, called
Milankovitch Cycles, are determined
by three factors: orbital eccentricity,
changes in the tilt of Earth's axis, and
the precession of Earth's axis.
Effect of Ocean
Circulation Patterns
(& Tectonics)
Antarctic Ice cap began forming ~35 Mya
Was this related to opening of Drake Passage
that occurred about the same time?
Long-term oxygen isotope record
Temperature and Ice Volume Effects
Colder
More Ice
Warmer
Less Ice
Development of the circum- Antarctic
current prevented warm ocean currents
from reaching Antarctica
Effect of Ocean Circulation Patterns
In the northern hemisphere…
~ 10 Mya
- Central American Seaway allowed
Pacific & Atlantic Oceans to mix
(& Tectonics)
~ 5 Mya
- Volcanism created the Isthmus of
Panama restricting exchange
between the two oceans
- the Gulf Stream began to intensify
Effect of Ocean Circulation Patterns
Ocean Conveyor
With the closing of the Isthmus of
Panama…
- The Gulf Stream transported saltier
water to the North Atlantic, making
waters there dense enough to sink &
drive the lower limb of the Conveyor
Jack Cook, WHOI
The Gulf Stream also transported warm,
moist air to the North Atlantic region
- moisture would enhance ice formation
- but warmth would deter it
CO2 Levels in Atmosphere
Primary Natural Controls:
• Volcanic Outgassing
CO2
• Burial of Organic C
CO2
• Continental Erosion
& Silicate Weathering
warmer
cooler
CO2
- reactions take CO2 out of atmosphere - into water
- adds nutrients to oceans - increase productivity
Continental Erosion
& Silicate Weathering
- reactions use up CO2
- adds nutrients to oceans
- increased productivity
~35 Mya India began
colliding with Asia
Uplift in the Andes
& western US was
also occurring at
this time
• Active uplift lead to very high levels of
weathering & erosion
- CO2 entered oceans - precipitated - formed limestones
- nutrients (ex. iron) increased algal productivity
• Ice formed at high elevations - also increased albedo
Glaciers are thick masses of
flowing ice
It all starts with
"Last year's snow"
For glaciers to form:
More snow falls in winter
than melts in summer
Snow transforms to ice
density
≈ 0.2
Firn
density
≈ 0.5
density
≈ 0.9
Ice
Taku Glacier, Juneau Icefield, Tongass National Forest, en:Alaska (USGS)
Snowflakes
change to "Old Snow" or "Corn Snow"
• Sublimation of lacy parts
(evaporation of a solid)
• Pressure Melting
Pressure Melting
under high pressure water shifts to its
denser phase = liquid
Melt/Freeze
Point of Water
low
pressure
0˚C
high
pressure
zone of
high
pressure
water
ice
water
-10˚C
ice
MELT
Water Refreezes
under low pressure water shifts to its
less dense phase = solid
Melt/Freeze
Point of Water
low
pressure
0˚C
high
pressure
water
water flows
away from
zone of
high
pressure
ice
water
-10˚C
ice
FREEZE
Firn
"Last year's snow"
• Dense, old snow - it has a sugary texture.
• Crystals are partly joined together
• Air pockets between crystals are still connected to each other.
Firn from South Cascade Glacier
http://emu.arsusda.gov/snowsite/default.html
Prominent layering in the firn is visible in the wall of a
large crevasse on Weissmiesgletscher, Switzerland.
Photo J. Alean. www.swisseduc.ch
Firn to Ice
snow
firn
ice
In ice, air passages
become isolated from
each other
With enough pressure
Ice flows
Glacial Motion
Friction slows speeds
along bottom & sides
ice
Ogives (curved structures) in Iceland Glacier
Curved Glacial Fronts
Oraefajökull icecap in southern Iceland
Perito Moreno Glacier, Argentina
Photos: www.swisseduc.ch
Glacial Motion
basal slip internal deformation
Zone of
Brittle Deformation
- Fracturing & Faulting
Brittle-Ductile Boundary
~50 m
Zone of
Plastic Deformation
- Intragranular gliding
net movement
Mechanisms:
Internal Deformation of Ice via:
1. Faulting (in brittle zone)
2. Intergranular gliding (due to pressure solution)
* 3. Intragranular gliding (in plastic zone -sliding of atomic planes)
* 4. Basal Slip (on water formed at base from pressure melting, frictional &/or geothermal heat)
Brittle Zone - Crevasses
Transverse Crevasses
Fox Glacier, New Zealand
Longitudinal Crevasses
Inside a crevasse - Erebus
Glacier Tongue, McMurdo Sound,
Antarctica
Photos: www.swisseduc.ch
Brittle Zone - Crevasses
Crevassing increases
as velocity increases
Variegated Glacier, Alaska
2.5 m/hr!
700 m/yr
< 10 m/yr
Glaciers in NW Spitsbergen
Photos: www.swisseduc.ch
Plastic Zone Flow Structures
Crusoe Glacier on Axel Heiberg
Island in the Canadian Arctic
Thompson Glacier on Axel Heiberg
Island in the Canadian Arctic
Photos: www.swisseduc.ch
Glacier Dynamics
Glacial Budget
ACCUMULATION = Addition of snow/ice
ABLATION = Loss of snow/ice
• melting
• sublimation
• calving
Both occur over entire glacier
but vary seasonally & spatially
Annual Glacial Budget
Seasonal Variation:
Winter - Accumulation dominates
Summer - Ablation dominates
Terminus position depends on total annual budget so if…
ACCumulation > ABLation
Glacier advances
ABLation > ACCumulation
Glacier retreats
ACCumulation = ABLation
Glacial front stalls
glacial terminus
Examples of Glacial Retreat
Annual Glacial Budgets
over time periods
ABL > ACC
Glacial Impacts on Landscape
Glacial Erosion Processes
1. Plucking
Melt/Freeze
Point of Water
low
pressure
0˚C
high
pressure
water
ice
-10˚C
water
ice
http://www.homepage.montana.edu/~geol445/hyperglac/eroproc1/
Glacial Erosion Processes
2. Abrasion
Debris in basal ice - Midtre Lovénbreen Glacier, Svalbard, Norway
photo: www.swisseduc.ch
Glacial Erosion
Effects of Plucking
& Abrasion
Glacial Striations
Roche moutonnée
Steilimmigletscher, Bernese Alps, Switzerland
Erosional Landforms
Glaciers carve pre-existing
narrow valleys into broad,
steep-sided valleys
U-shaped Glacial Valley
V-shaped River Valley
Geiranger, Norway
Glacial Erosion
Effects of Abrasion
Production of fine sediments
Serac® Genuine Glacial Milk ®
Tasman Glacier, New Zealand
(Coarse sediments are also produced - by plucking)
Sediments are added to glaciers by erosion & also
quite a lot is added by mass wasting onto the glacier
Avalanches across alpine glacier
Glacial Sediments
Ice-lain deposits are generally
POORLY SORTED
Khumbu Glacier, Nepal
Ice carries all sizes equally well
The Great Glacial "Conveyer Belt"
Ice carries all sizes
equally well & drops
them all together
zone of net
ablation
zone of net
accumulation
sediments
buried under
new layers
of snow
Glacial Budget - Spatial Variation
Equilibrium Line
Net accumulation
last year's snow remains
Net ablation
Glacial Budget - Spatial Variation
Higher Latitudes & Altitudes
COOLER
ACCumulation > ABLation
Lower Latitudes & Altitudes
WARMER
ABLation > ACCumulation
Zone of
ACCUMULATION
ACC > ABL
Zone of
ABLATION
ABL > ACC
Equilibrium Line
ACC = ABL
glacial terminus
The Great Glacial "Conveyer Belt"
In Zone of Net Accumulation
Seasonal interlayering of snow & sediment
sediments
buried under
new layers
of snow
Glacial margin, southern Bylot Island, west of Aktineq, Nunavut.
Geological Survey of Canada
The Great Glacial "Conveyer Belt"
In Zone of Net Ablation
Snow & ice
melt leaving
sediments
behind
Ice-lain Deposits = TILL
Supraglacial & Englacial Transport
(on top)
(within)
Ablation Till
Subglacial Transport
(under)
Lodgement Till
Depositional Landforms - Moraines
Ridges or sheets of till
Usually -
Ridges of Till
ex. if glacial front stalls,
ridge forms = end moraine
if instead, steady retreat,
sheets of till cover the
valley floor = Ground Moraine
Depositional Landforms - Moraines
Extent of
Kansan
glaciation
Long Island is a
terminal moraine
- marks the furthest advance
of the Wisconsinan Glaciation
Another type of Ice-lain deposit = Glacial Erratics
Ice-lain boulder
Most Glacial
Sediments in an area
are locally derived
A really great analogy… really…
The wreck of the M&M Railroad
M&M
M&M
This glacial erratic is a rare
one from the Adirondacks
M&M
glacial advance - "rolling the snowball"
Another type of Ice-lain deposit = Glacial Erratics
Ice-lain boulder
Most Glacial
Sediments in an area
are locally derived
A really great analogy… really…
The wreck of the M&M Railroad
M&M
M&M
This glacial erratic is a rare
one from the Adirondacks
M&M
glacial advance - "rolling the snowball"
Another type of Ice-lain deposit = Glacial Erratics
Ice-lain boulder
Most Glacial
Sediments in an area
are locally derived
A really great analogy… really…
The wreck of the M&M Railroad
M&M
M&M
This glacial erratic is a rare
one from the Adirondacks
M&M
glacial advance - "rolling the snowball"
Another type of Ice-lain deposit = Glacial Erratics
Ice-lain boulder
Most Glacial
Sediments in an area
are locally derived
A really great analogy… really…
The wreck of the M&M Railroad
M&M
M&M
This glacial erratic is a rare
one from the Adirondacks
M&M
melting and retreat
Another type of Ice-lain deposit = Glacial Erratics
Ice-lain boulder
Most Glacial
Sediments in an area
are locally derived
A really great analogy… really…
The wreck of the M&M Railroad
M&M
M&M
This glacial erratic is a rare
one from the Adirondacks
M&M
melting and retreat
Glacial Sediments
Meltwater-lain deposits = OUTWASH
Austre Brøggerbreen, Norway
Water-lain deposits
are generally
WELL SORTED
Liz & Drew - Colgate Geology OC 2002
Sand & Gravel Quary - Near Gloversville, New York
Depositional Landforms
Outwash Plains
- broad, flat valley floors
- filled with thick layers of
sands and gravels
Thompson Glacier, Axel Heiberg Island,
Canadian Arctic
Tazman River, South Island, New Zealand
"Ice-Contact Stratified Drift"
Outwash deposited in contact with ice
ICSD Landforms
kames
kettles
eskers
Depositional Landforms
ICSD Landforms - Kames
Sediments deposited by
supraglacial streams…
Sediments deposited by
supraglacial streams into
holes in the glacier
remain as conical hills
after glacier ablates
… is deposited into crevasses
Depositional Landforms
ICSD Landforms - Kettles
Kettles are like "Reverse Kames"
Sediments deposited by
outwash streams around
stranded blocks of ice in
the outwash plain remain
as depressions
Depositional Landforms
ICSD Landforms - Eskers
Deposition within supra-, en-, and subglacial streams…
Thompson Glacier push moraine Axel Heiberg Island, Canada
Sediments deposited by
interglacial streams remain
as sinuous ridges after the
glacier ablates
2 Main Types of Glaciers
Alpine glaciers
Continental glaciers
This is what NY state would have
looked like 21,000 years ago
Impacts on our area
• thick glacial deposits
- good aquifers
- good soils
- flood prevention
• glacial topography
- broad valleys &
rolling hillsides
ice sheets ~ 2 km thick
- steep valley walls
The Finger Lakes
Flooded U-shaped Valleys
Oblique view of the Finger Lakes
from Oneida Lake toward the
southwest. The Valley Heads
Moraine is the light colored area
to the top-left of the image
Image: NASA
Dammed on their south ends
by the Valley Heads Moraine
(position indicated by red line)
R. W. Allmendinger © 2006-2010
DEM of
Local Topography
showing glacial
landforms
Valley Heads Moraine &
Munnsville Kame Complex
Broad, U-shaped valleys
/ Outwash planes
Munnsville &
Madison-Bouckville
Outwash Plain
Madison Kettle Holes
& Kettle Lakes
Solsville-Oriskany Falls
Kame Complex