Midterm Prep Flashcards
The first known ice age took place in the _____. This is known as the ____ ____
archean
snowball earth
the last ice age is referred to as the ____ ____ ___
last glacial maximum (LGM)
when did the LGM take place?
25-20ka
*ka= 1000s yrs
Generalizations of an ice age:
- ___ global sea level (__m)
- ____ (colder/ warmer) climate
- ecological ____
- extensive ice sheets to ___-___
- ____ glaciation
lower (120m)
colder
changes
mid-latitudes
periodic
Explain the origins of “ice age” theory. Who led most of this?
Early scientists were confused by poorly sorted sediments and boulders. The controversial ideas that glaciers once covered Europe and N. America arose.
This was led by Louis Agassiz
T/F
By the 19th century, the idea of extensive past glaciation was more accepted
true
Once ideas of past glaciation were more accepted, what did the focus shift to? What was the consensus?
focus was shifted to # of glacial events. The consensus was 4 glacial events in N. America and Europe
What is “Etudes sur les glaciers”?
“A study on Glaciers”
A book by Louis Agassiz, principle of uniformitarianism introduced
What is Astronomical Theory? What is it often known as?
ie Milankovitch theory
Idea that Earth’s orbit around the sun is not constant, and that these changes in orbit lead to spatial and temporal difference in distribution of energy at Earth’s surface
The 3 aspects of Milankovitch theory are:
1
2
3
- Eccentricity (shape of orbit)
- Obliquity (tilt)
- Precession (wobble)
Paleoceanography=
the study of the oceans as they were in the past, from a few hundred years to billions of years ago, with the aim to reconstruct their physical, chemical and biological character
T/F
stable isotopes decay
false!
stable isotopes do NOT decay
Physical, chemical, and biological transformations lead to changes (ie. ______) in the relative abundance of _____
fractionation
isotopes
Which is more likely to evaporate, water with 16O or water with 18O? Condense?
Water with 16O is more likely to evaporate than water with 18O (because it’s lighter)
Water with 18O is more likely to condense than water with 16O
______ secrete at CaCO3 “test” shell
foraminifera
What is a glacier?
= a body of ice that flows under the influence of gravity and its own mass
What are 2 examples of ice movement that could classify it as a glacier?
Deformation of ice, sliding (*under the influence of gravity and its own mass)
Glaciers will form when ice accumulation is ____ (less/ greater) than ice loss. What is this called?
Glaciers will form when ice accumulation is GREATER than ice loss.
= Accumulation
T/F
Studying glaciers can be useful, but can’t give us a baseline for future climate changes
False
They can preserve highly resolved records of past environments that provide a baseline for future changes (temp, dust, pollution,
volcanism)
T/F
glaciers and ice sheets interact strongly with the climate system through a variety of feedbacks
true
Is it possible to find evidence of glaciers across the northern hemisphere?
Yes!
Surface sediments associated with growth and decay of ice sheets are widespread across the N. hemisphere
List some things that are factors of the distribution of glaciers
elevation, aspect/ topography, continentality, marine currents, ocean temps
T/F
avalanches, calving, sublimation, and geothermal heat flux don’t have much impact on the distribution of glaciers because they’re relatively small-scale
FALSE
these all play a role in shaping the distribution of glaciers
mass balance=
net difference between accumulation and ablation over time (usually winter/ summer cycle)
Glaciers will recede when ice accumulation is ____ (less/ greater) than ice loss. What is this called?
LESS
= ablation
what is the density of snow?
= 0.05g/cm^3
Explain what firnification is.
What’s the density of firn?
= a process when snow survives a year of summer melt to become firn
Density of firn ~ 0.8g/cm^3 (void space reduced)
The density of glacial ice is ___g/cm^3 (____ dense than snow and firn)
Are there any void spaces? Is there exchange with the atmosphere?
0.9g/cm3
MORE
All void spaces are isolated. There is no exchange with the atmosphere
Thermal regime determines:
determines how material is eroded and transported, glacier velocity, and geomorphic legacy of glaciations (landforms)
Cold-based glacier=
frozen to bed, no subglacial water
warm-based glacier=
Basal ice is at high pressure, so above melting point. This results in the presence of liquid water at the base of the glacier
Polythermal ice=
cold/ warm based in different places and times
A body of ice is greater than 50,000km^2. What is it classified as?
An Ice sheet
A body of ice is less than 50,000km^2. What is it classified as?
An ice cap
Icefields=
the glacier fills and elevated basin (controlled by topography), commonly with radiating outlet valley glaciers
Cirque glacier=
occupies a small basin on a mountain slope
Piedmont glacier=
lobe-shaped glacier formed when steeper ice spills out into a broad lowland
Tidewater Glacier=
a glacier that terminates at sea level into the ocean
Calving=
ablation of glacier ice by breaking off into the ocean
There is only one movement mechanism possible for cold-based glaciers. What is this motion called? Describe it
= internal deformation (“creep”): change in shape of ice crystals in response to an applied load (strain)
Basal sliding is a type of glacier motion, explain how it works
basal sliding= sliding along the interface between ice and substrate
- strongly controlled by presence of water, whereby glacier can be locally detached from its bed
What is subglacial deformation? What largely controls it?
= deforming of sediments underlying base of ice, which contributes to the overlying glacier
- strongly controlled by presence of water and nature of underlying materials
Why do crevasses form?
They form when ice can’t deform fast enough to an applied stress, resulting in brittle failure
T/F
internal deformation heals surface fractures where crevasses form
true
What is a glacier surge?
transient episode of rapid movement 10-100x the normal velocity of the glacier
- Lead to a rapid transfer of mass from high to low elevation
T/F
glacier surges are directly related to climate
false
glacier surges are internally driven, not directly related to climate
How long do glacier surges last?
Can last for months up to ~1yr, separated by many years of quiescence
Looped moraines=
moraines from tributary glaciers that get stretched out by the surging glacier
Surge-front propogation:
indicates buildup of ice reservoir, which will eventually be rapidly transferred downslope during a surge
What can happen if there’s lots of water at the base to facilitate basal sliding?
= high basal water pressure!
This can locally approach ice overburden pressure
Till=
a generic term for unsorted, generally unstratified sediment, directly deposited by a glacier
What are the 3 principles for till-formation?
- Lodgement
- Deformation
- Melt-out
Describe “lodgement” in the till-formation process
= the plastering of debris along the base of moving ice
- occurs when frictional resistance exceeds the shear stress at the base of the ice
Describe “deformation” in the till-formation process
= change in the shape and orientation of sediments
Subglacial sediment deformation will occur when:
1
2
- the glacier is coupled to the underlying sediment
- shear stress from overlying ice exceeds the shear strength of the underlying sediment
Describe “melt-out” in the till-formation process
= the slow release of sediment from basal ice due to melting
Debris-rich ice will be deposited during melting at the ___ of the glacier
base
Subglacial erosion=
processes occurring at interface between ice and ground surface that promote the breakdown of surface materials.
There are 2 main processes
What are the 2 main processes of subglacial erosion?
- Abrasion= wearing down of bedrock by direct contact b/w particles carried by ice and the surface
- Plucking/ Quarrying= fracture due to stress build-up leads to detachment of rock fragments that are then entrained (carried away)
What are 2 landforms associated with erosion by abrasion?
- Striation
- Glacier polish
Striation=
particles carried by ice directly abrade thin linear grooves into bedrock or clasts. Appear smooth, but are the result of a series of microfractures due to a build-up of stress
Glacier Polish=
polishing of bedrock surfaces by action of smaller particles (carried by ice) being dragged across the bedrock
Landforms associated with erosion by plucking are called:
Roche Moutonee
(rock looking like a sheep at rest)
Aretes, horns, U-shaped valleys, and hanging valleys are all landforms associated with ____
erosion
Arete=
A ridge that forms between cirques
Horns=
erosional remnant of glacier erosion (high triangular peak)
U-shaped valleys=
longitudinal valleys produced by widening & deepening of pre-existing valleys by glacial erosion
Hanging valley=
a tributary valley that enters a larger U-shaped valley
Equifinality=
principle that in open systems a given end state can be reached by many potential means
Drumlins=
glacially elongated hills, generally w/ steep stoss side and gently sloping lee side
teardrop shape in planform
Flutings are __glacial ____. Describe what they might look like
Like drumlins, but stretched, and lacking teardrop planform and “inverted spoon” cross-section.
- Parallel ridges, tens of cm to a few m high and wide, & tens of m in length
Moraines=
ridges or mounds of glacial material deposited at, or close to, ice margins
Hummocky moraine=
topographically, a strongly undulating surface of irregular, steep, small hills and hollows
Gilbert Deltas provide evidence of past ___ level
water
dropstones=
clasts carried by floating ice & released as ice melts
varves=
annual couplet of fine sediment recording seasonal changes in deposition
___ __ ___ developed the study of varves for glacial geochronology
Gerald de Geer
What does the term “palimpsest” mean?
refers to something reused or altered but still bearing visible traces of its earlier form
