ASBOG - Association of State Boards of Geology Geomorphology and Quaternary Geology Questions and Answers — Questions and Answers
Question 1: A geologist mapping surficial deposits in a formerly glaciated region identifies a long, sinuous ridge composed of well-sorted sand and gravel. This feature can extend for many kilometers. What is this landform most likely to be?
- A terminal moraine
- An esker (Correct answer)
- A drumlin
- A kame
Correct answer: An esker
An esker is a long, winding ridge of stratified sand and gravel which formed in meltwater tunnels underneath, within, or on top of glaciers. As the glacier retreats, the sediment deposited by the subglacial stream remains as a distinct ridge. Terminal moraines are typically poorly sorted till, drumlins are elongated hills of till, and kames are irregular mounds of sand and gravel.
Question 2: The cyclical variations in Earth's orbital eccentricity, axial tilt (obliquity), and precession, which are understood to be a primary driver of Quaternary glacial-interglacial cycles, are known as:
- Wilson Cycles
- Davisian Cycles
- Milankovitch Cycles (Correct answer)
- Bowen's Reaction Series
Correct answer: Milankovitch Cycles
Milankovitch Cycles describe the collective effects of changes in the Earth's movements on its climate over thousands of years. These cycles—eccentricity (orbital shape), obliquity (axial tilt), and precession (wobble)—alter the amount and distribution of solar radiation reaching Earth, influencing the advance and retreat of ice sheets during the Quaternary Period.
Question 3: Which of the following geomorphic features is formed by deposition on the inside bend of a meandering river where water velocity is lowest?
- A cut bank
- An oxbow lake
- A point bar (Correct answer)
- A riffle
Correct answer: A point bar
A point bar is a depositional feature made of alluvium that accumulates on the inside bend of a meandering river. The water velocity is slower on the inside of the bend, reducing the stream's capacity to transport sediment and causing it to be deposited. A cut bank is an erosional feature on the outside bend, and an oxbow lake is an abandoned meander loop.
Question 4: Extensive, thick blankets of homogenous, unstratified, wind-blown silt that cover large areas of the mid-latitudes are known as:
- Till
- Loess (Correct answer)
- Outwash
- Alluvium
Correct answer: Loess
Loess is a clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. These deposits are typically associated with Quaternary glaciations, where glacial grinding produced fine 'rock flour' that was picked up by winds from barren outwash plains and deposited over vast areas.
Question 5: A geologist studies a coastline characterized by a series of uplifted, flat surfaces resembling steps, known as marine terraces, which are located at various elevations above the current sea level. What is the most likely geologic history of this area?
- A submergent coastline experiencing a relative rise in sea level.
- A stable coastline dominated by a prograding delta.
- A passive margin with consistent sediment accumulation.
- An emergent coastline experiencing tectonic uplift or a relative fall in sea level. (Correct answer)
Correct answer: An emergent coastline experiencing tectonic uplift or a relative fall in sea level.
Marine terraces are former wave-cut platforms and beaches that are now elevated above the current sea level. Their presence indicates an emergent coastline, where the land has risen relative to the sea. This relative change is typically caused by tectonic uplift in active margin settings, sometimes combined with global (eustatic) sea-level fluctuations.
Question 6: What is the term for the steepest angle, measured from the horizontal, at which a pile of unconsolidated granular material, such as sand or gravel, will remain stable without slumping?
- Angle of repose (Correct answer)
- Dip angle
- Angle of incidence
- Shear angle
Correct answer: Angle of repose
The angle of repose is the maximum slope at which loose, solid material will remain in place without sliding. It is a critical property in geomorphology and geotechnical engineering for assessing the stability of slopes, and it varies depending on factors like particle size, shape, and moisture content.
