Geology - Test 4
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- What is a glacier?
- A flacier is a thick ice mass that forms over hundreds or thousdands of years. It originates on land from the accumulation, compaction, and recrystallization of snow
- Approximately what percentage of Earth's land area is covered by glaciers today?
- About 10%
- About how much would sea level rise if all of today's glaciers melted?
- about 200 ft!
- About what percentage of Earth's land area was covered by glaciers during the Great Ice Age?
- 30%
- About how much lower was sea level during the Great Ice Age?
- 300feet
- Explain some key differences between alpine glaciers and continental ice sheets.
-
Alpine Glaciers
*slow moving
*probably streams where there before
Ice Sheets
*large scale
*flow out in all directions from one or more snow-accumulation centers - About how fast do glaciers flow?
- centimemters a day
- Discuss the budget of a glacier, and how a glacier responds to a changing budget.
- the glacial budget - is the balance, or lack of balance, between accumulation at the upper end of the clacier and loss at the lower end
- In plain English, what is ablation?
- loss of ice and snow from a glacier
- When, if ever, does glacial ice flow backward?
- glacier ice ALWAYS flows forward, the SNOUT will sometimes move backwards
- What sorts of work do glaciers do?
- Erosion, Transportation, Deposition
- Using the correct jargon, describe how glaciers erode the land.
-
Plucking - water flows into rock joints under glacier, freezes, wedging up chunks of rocks, glacier snags to --- rocks, carries them a long its base
Abrasion - Rocks carried by glacier scratch underlying rock
„X Striation ¡V scratches rock
„X Polishing ¡V abrasion by fine-grained material at base of glacier (works like sand paper) - What is "rock flour?"
-
o Pulverizing of rock by glacial flow makes wide range of clast sizes/ from boulders to very tiny “rock flour”
o Streeams leaving glacier sometimes are milky white due to load of rock flour - Flowing liquid water sorts clasts by size. Why doesn't the flowing ice in a glacier sort clasts?
-
• Glaciers have much greater competence than rivers, so can carry everything from rock flour to largest boulder
moving ice can not sort sediment - Describe till.
- materials deposited directly by the glcaier, which are known as till.... till is deposited as glacial ice melts and drops it load of rock fragment
- What is a moraine?
-
land form made of till -
simply layers or ridges of sills - end moraine
- is a ridge of till that forms at the terminus of a glacier
- terminal moraine
- a type of end morraine, marks the furthest advance of glacier -- a hill of till
- recessional moraine
- type of end moraine - end moraine left by retreating glacier that periodically stabilized before retreat resumed
- ground morraine
-
dispersed till left by retreating glacier whose snout didnÂ’t stabilize long enough for hill of till to form
so crap laying around kinda ---it has a leveling effect, think grat lakes regions - lateral moraine
-
the material left as ridges a long the sides of the valley -
form on sides of alpine glaciers by plucking valley walls and by rock falls from above - medial moraine
-
formed when two valley glaciers coalesce to form a single ice stream, these create stripes and stuff
„X When tributary glacier joins main glacier, one of its lateral moraine becomes a medial morrain (because it winds up in middle of --- glacier) - Explain the origin of medial and lateral moraines.
-
medial, when two lateral moraines meet,
lateral--- the stuff from the sides and stuff - What was the origin of a glacial erratic?
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when boulders are found in the till or lying free on the surface, they are called glacial erratics if they are different from the bedrock below...
o Glacial erratic = boulder (in till or on glacially eroded surface that is different from rocks upon which it rests) was brought in from elsewhere - Explain how the cross-section shape of an alpine stream valley differs from that of an alpine glacial valley.
- *
- Arete
- a narrow, knifelike ridge separating two adjacent glaciated valleys
- horn
- a pyramid-like peak formed glacial action in three or more cirques surrounding a mountain summit
- hanging valley
- a tributary valley that enters a glacier trough at a considerable height about the floor of the trough
- glacial trough
- a mountain valley that has been widened deppened, and straightened by a glacier
- tarn
- a small lake in a cirque
- cirque
- an amphitheater-shaped basin at the head of a glaciated valley produced by frost wedging and plucking
- During the Great Ice Age, Earth had continental ice sheets. Do continental ice sheets exist today? Where?
- greenland and antarctica
- When did the Great Ice Age occur?
- ?
- About when did the Great Ice Age end?
- ?
- Describe a drumlin, including its shape, composition, and origin.
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streamlined asymmetrical hills composed of till, they occur in clusters, it is thought that drumlins originate when glaciers advance over previously deposited drift and reshape the material
 Drumlin – “spoon-shaped” deposits of glacier Till.
• Elongated in direction of flow of glacier - Describe an esker, including its shape, composition, and origin.
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ridges are deposited by meltwater rivers flowing within/on/beneat a mass of motionless/stagnant glacia ice --- only course material can settle, so it's snake of gravel and sand
• Esker – curving hill made of sediment deposited by stream that flows, in, or under glacier, sediment deposited by stream, so is sorted – not till - Explain what determines whether the snout of a mountain glacier will advance or retreat. That is, explain the “budget” of a glacier.
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accumulation > ablation - advance
accumulation < ablation - retreat - Explain the origin of kettles ("kettle lakes").
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 During glacial retreat, large block of unmelted ice are “stranded in front of glacier” <dead ice> - detached from ice sheets
• While dead ice is melthing, it can be partly buried in outwash
• Sediment huild up around the dead ice
• The shape of the dead ice is retained by the surrounding sediment, the depression is a kettle, if it contains a lake, it’s kettle lake - Name the glacial stages and interglacial stages of the Great Ice Age.
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Glacial Stage Interglacial Stage
Wisconsin Recent
Illionoisan Sangamon
Kansan Yarmouth
Nebraska Aftonian - When did the "Recent" interglacial stage begin?
- 18,000 years ago
- Distinguish between proglacial lakes and pluvial lakes.
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pluvial - a lake formed during a period of increased rainfall, for example - this occured in many nonglaciated areas during periods of ice advance elsewhere
proglacial - proglacial lakes formed in front of melting ice sheets - What was the origin of Lake Agassiz?
- ?
- Where was Lake Agassiz and about how long did it exist?
- ?
- What are Milankovich Cycles?
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o Milankovich cycles = orbital movements (of earth) that govern temperature contrast between the seasons
„X Eccentricity (stretch) ¡V of Earth¡¦s orbit. Orbit changes from nearly circular to elliptical and back over a cycle of 100,000 years
„X Obliquity (tilt) ¡V angle of inclination of Earth¡¦s axis varies from about 22.5 degrees to about 24.5 degrees over a cycle of 41,000 years
„X Process (wobble) ¡V accuses Earth¡¦s north pole to gradually point to different spots in the sky over a cycle of 26,000 years - What is the apparent relationship between Milankovich Cycles and the Great Ice Age?
- ?
- Explain how the “ice age” is actually not over and glacial ice advance is expected again.
- ?
- What is wave base?
-
• Wave base – depth below which water is calm, even though wave is passing over ---
o Depth to wave base = ½ x wavelength - Define wavelength.
- o Wave length (horiztonal distances between crests of the two waves)
- What is wave refraction?
- a change in direction of waves as they enter shallow water. The portion of the wave in shallow water is slowed, which causes the wave to bend and alighn with the underwater contours
- Explain the relationships between wave refraction and coastal erosion and deposition.
- ?
- Explain the origin of a wave-cut platform.
- a bench or shelf along a shore at sea level, cut by wave erosion
- What controls the depth (below sea level) at which a wave-cut platform could form?
- the wave length
- Explain the concept that beaches have a budget of sand.
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 Many natural beaches keep a – balanced sand budget
• Beach shrinks or grows from season to season, but there is a long term balance
 But humans disturb a beach’s sand budget
• Reservoir behind damn traps sand that would have been delivered to coast
• Beach is starved - What is the origin of longshore drift?
- „X Swash and backwash cause water and sand to move in a zig-zag patter. Net results are
- What is the origin of a longshore current?
- „X Swash and backwash cause water and sand to move in a zig-zag patter. Net results are
- Beaches have been referred to as "rivers of sand." Why is this an apt analogy?
- why is this an appropriate analogy - because the beaches moves and stuff
- Many beaches are dominated by grains of quartz sand. What is the source of all this quartz, and how does the quartz get onto the beaches?
- from rivers and stuff duh---quartz is resistant to breakdown
- What is the relationship between shoreline erosion and the construction of dams on rivers?
- ?
- What is a groin?
- a short wall built at a right angle to the seashore to trap moving sand
- Explain the effect of groins on longshore drift.
- a sand glutted area and a sand starved area
- Emergent/Submergent
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emergent = steps
submergent = estuaries - Explain the relationships between stress, strain, elastic limit, and earthquakes.
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earthquakes - is the vibration of Earth produced by the rapid release of energy...generally caused by slippage
------- ---
original position
build up strain
rupture
strain released
----
??? - Distinguish between an earthquake's focus and its epicenter.
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focus - the zone within Earth where rock displacement produces an earthquake
epicenter - the location on earth's surface that lies directly above the focus of an earthquake - What are the three main types of seismic waves?
- P S L
- Which types of seismic waves are body waves and which are surface waves?
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p and s = body
l = surface - In the name "p-wave," what does "p" stand for?
- primary
- In the name "s-wave," what does "s" stand for?
- secondary
- Which kind of body wave travels by compression (and rarefaction)?
-
p waves
think of a slinky
- - - - ------ - - - - ---- - - - - - Which type of seismic body wave travels by shearing the material through which it is traveling?
- ?
- Which type of seismic body wave cannot travel through a liquid?
- s waves
- Explain how we can deduce that Earth has a molten outer core.
- because of the shadow zone
- Which is the fastest kind of seismic body wave?
- p waves
- Explain the method of triangulation to locate an earthquake epicenter.
- circle - circle - circle
- What is "amplitude"?
- Greatness of size; magnitude.
- What does the Richter Scale attempt to determine?
- in 1935 charles richter of the california institue of technology developed the first magnitude scale using seismic records to estimate the relative sizes of earthquakes= === based on the amplitude of the large seismic wave recorded on a seismogram
- Compare the maximum amplitude of seismic waves from an earthquake with Richter Mignitude = 6 to the maximum amplitude of seismic waves from an earthquake with Richter Magnitude = 7.
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6.5 - 100
6 - 50
5.5
5 - 25
4.5 - 10
4 - 5
.....2
.....1
......5 - What was the approximate Richter Magnitude of the largest earthquakes ever recorded? About how much energy did they release?
- 9, 1 billion tons of tnt
- Do rigid or flexible building materials tend to perform better in earthquakes? Would you expect a woodframe house or a brick house to survive better in a quake?
- flexible - wood
- Seismic waves become amplified as they move through what sorts of geologic materials?
- soft sediments amplify seismic waves
- What is liquefaction? Is it "good" or "bad"? Why?
-
hmmm milkshake
• Wet soils and wet sediment can undergo liquefaction, turning them briefly into a milkshake like fluid that cannot support structures
yeah it's bad - What is a tsunami?
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„X Tsunami ¡V (seismic sea waves) ¡V can move out at great speed through ocean water and ---- sea floor is ------- by a quake. When tsunami reached shore, wave height can increase to more than 50 feet
- the japanese word for a seismic sea wave ---
a rapidly moving ocean wave generated by earthquake activity and capable of inflicting heavy damage in coastal regions - About how fast can tsunami travel in the open ocean?
- 300-600 mils per hours
- What is the basis for long-term earthquake prediction?
- Long-range predictions are based on the premise that earthquakes are repetitive or cyclical, like the weather. In other words, as soon as one earthquake is over, the continuing motions of Earth's plates begin to build strain in the rocks again until they fail once more.
- When speaking of "long-term" earthquake prediction, what is meant by "long-term"?
- 30---100 or more years
- Which section of the San Andreas Fault is estimated to have the highest probabilty of experiencing a major earthquake in the long-term?
- Parkfield --- 90% ---every 22 years