ASBOG Geomorphology and Quaternary Geology 5 — Questions and Answers
Question 1: Solifluction is a periglacial mass-wasting process that occurs when:
- Frozen ground thaws and saturated soil slowly flows downslope (Correct answer)
- Wind erodes loose sediment from frozen surfaces
- Ice wedges expand and push soil laterally
- Permafrost melts catastrophically in thermokarst lakes
Correct answer: Frozen ground thaws and saturated soil slowly flows downslope
Solifluction occurs when the active layer above permafrost thaws and becomes saturated, causing slow downslope flow of waterlogged soil.
Question 2: Which of the following best describes a braided stream?
- A single sinuous channel with well-developed meanders
- Multiple interconnected channels separated by mid-channel bars (Correct answer)
- A straight channel with alternating pools and riffles
- A distributary network on a delta plain
Correct answer: Multiple interconnected channels separated by mid-channel bars
Braided streams have multiple shifting channels divided by transient bars of coarse sediment, typically reflecting high sediment load and variable discharge.
Question 3: Tafoni are weathering features consisting of cavernous hollows in rock surfaces, formed primarily by:
- Frost wedging in cold climates
- Salt crystallization and differential chemical weathering (Correct answer)
- Abrasion by wind-driven sand
- Biotic erosion by lichens and mosses
Correct answer: Salt crystallization and differential chemical weathering
Tafoni form through salt weathering and differential chemical weathering, creating honeycomb or cavernous textures on rock surfaces.
Question 4: What is the primary mechanism that forms oxbow lakes?
- Tectonic subsidence along a river valley
- Cutoff of a meander loop as a river straightens its course (Correct answer)
- Glacial erosion creating elongated depressions
- Dissolution of carbonate bedrock beneath a river channel
Correct answer: Cutoff of a meander loop as a river straightens its course
Oxbow lakes form when a river cuts through a meander neck during a flood, abandoning the old loop which becomes isolated as a crescent-shaped lake.
Question 5: Which Quaternary stratigraphic boundary is formally defined at the Global Boundary Stratotype Section and Point (GSSP) in the Vrica section in Italy?
- Pleistocene-Holocene boundary at ~11,700 years ago
- Pliocene-Pleistocene boundary at ~2.58 Ma (Correct answer)
- Miocene-Pliocene boundary at ~5.33 Ma
- Early-Middle Pleistocene boundary at ~0.77 Ma
Correct answer: Pliocene-Pleistocene boundary at ~2.58 Ma
The base of the Quaternary (Pleistocene) is formally defined at 2.58 Ma at the Vrica GSSP in Italy, marked by a paleomagnetic reversal.
Question 6: Desert pavement is a surface layer of tightly packed stones that forms through:
- Deflation removing fine particles and concentrating coarse clasts at the surface (Correct answer)
- Evaporation of groundwater cementing surface gravels
- Frost heaving pushing coarser material upward
- Alluvial deposition of coarse lag material during flash floods
Correct answer: Deflation removing fine particles and concentrating coarse clasts at the surface
Desert pavement forms primarily by deflation, where wind removes fine-grained material, leaving a lag of coarser clasts that armor the surface against further erosion.
Question 7: A striated boulder transported far from its source rock type is called an:
- Erratic (Correct answer)
- Dropstone
- Ventifact
- Flatiron
Correct answer: Erratic
A glacial erratic is a boulder transported by ice and deposited far from its bedrock source, often identifiable because it differs in rock type from local bedrock.
ASBOG Geomorphology and Quaternary Geology 5
Solifluction is a periglacial mass-wasting process that occurs when: