ASBOG Geomorphology and Quaternary Geology 4 — Questions and Answers
Question 1: Isostatic rebound (glacial isostasy) refers to:
- The subsidence of the crust under the weight of a glacier
- The upward movement of the crust after glacier removal (Correct answer)
- Horizontal crustal movement due to ice loading
- Thermal expansion of bedrock beneath ice sheets
Correct answer: The upward movement of the crust after glacier removal
Isostatic rebound is the upward rise of Earth's crust after the removal of glacial ice load, a process still ongoing in Scandinavia and Canada.
Question 2: Which feature is characteristic of karst topography?
- Broad alluvial plains
- Sinkholes, caves, and disappearing streams (Correct answer)
- Deeply incised river canyons
- Glacially polished bedrock surfaces
Correct answer: Sinkholes, caves, and disappearing streams
Karst topography develops on soluble rocks like limestone and is characterized by sinkholes, caverns, springs, and disrupted surface drainage.
Question 3: A kettle hole is formed when:
- Glacial meltwater erodes through a moraine
- A buried block of glacial ice melts, causing the overlying sediment to collapse (Correct answer)
- Outwash sediment is deposited around an ice core
- A subglacial meltwater channel is abandoned
Correct answer: A buried block of glacial ice melts, causing the overlying sediment to collapse
Kettle holes form as depressions in glacial outwash plains when stagnant ice blocks buried by sediment melt out.
Question 4: What does a negative or falling stream gradient indicate in longitudinal profile analysis?
- The stream is at grade and not eroding
- A knickpoint may be present due to differential resistance or base level change (Correct answer)
- The stream is actively aggrading its bed
- The watershed is losing water to groundwater
Correct answer: A knickpoint may be present due to differential resistance or base level change
A steepened reach or knickpoint in a stream's longitudinal profile indicates differential erosion, resistant rock, or upstream migration of a base-level change.
Question 5: The Milankovitch cycles that drive glacial-interglacial cycles include all of the following EXCEPT:
- Eccentricity of Earth's orbit (~100,000 years)
- Axial precession (~26,000 years)
- Solar luminosity changes (~11-year sunspot cycle) (Correct answer)
- Axial obliquity (~41,000 years)
Correct answer: Solar luminosity changes (~11-year sunspot cycle)
Milankovitch cycles involve eccentricity, obliquity, and precession of Earth's orbit and axial tilt, not short-term solar luminosity cycles.
Question 6: Alluvial fans typically develop where:
- Rivers enter broad coastal plains
- Streams emerge from confined canyons onto open piedmont slopes (Correct answer)
- Glaciers melt at their terminus
- Longshore currents deposit sediment
Correct answer: Streams emerge from confined canyons onto open piedmont slopes
Alluvial fans form at the base of mountain fronts where confined streams spread out, lose velocity, and deposit coarse sediment in a fan shape.
Question 7: The Younger Dryas event (~12,900–11,700 years ago) represents:
- A brief warm interval within the Last Glacial Maximum
- A sudden return to near-glacial conditions during the last deglaciation (Correct answer)
- The onset of the Wisconsin glaciation
- The final melting of the Laurentide Ice Sheet
Correct answer: A sudden return to near-glacial conditions during the last deglaciation
The Younger Dryas was a rapid return to cold, near-glacial conditions that interrupted the warming trend of the last deglaciation.
ASBOG Geomorphology and Quaternary Geology 4
Isostatic rebound (glacial isostasy) refers to: