GEO 200: Glaciology, Glacial Landforms, and Fluvial Geomorphology

Comprehensive practice flashcards covering glaciology, glacial mechanics, erosional and depositional glacial landforms, ice sheet processes, and fluvial geomorphology from physical geography lectures and study guides.

What are the four progressive stages of snow transformation into glacial ice, and what is the air content at each stage?

1. Fresh snow: $90\%$ air (six-armed structure keeping crystals separated)
2. Granular snow: $50\%$ air (snowflakes settle, break apart, partially melt, and sublimate)
3. Firn (or névé): $25\%$ air (several seasons of accumulation packed by gravity)
4. Glacial ice: Less than $20\%$ air (ice crystals melt and refreeze to fill air spaces)

What is the formal definition of a glacier?

A large mass of ice formed from the accumulation of snow that flows slowly downslope.

Why do glaciers fail to form in periglacial environments?

Glaciers do not form in periglacial environments because snow melts in the summer or because there is insufficient snowfall.

What are the two primary mechanisms by which glaciers move downslope, and which is the dominant method?

Glaciers move downslope by plastic deformation and basal sliding. Plastic deformation is the dominant method, and some glaciers never move by basal sliding.

At what depth does glacial ice become plastic, and what forms in the brittle zone above this depth?

From the glacier surface down to $60\,\text{m}$, ice behaves brittly. Cracks called crevasses form at the surface where the glacier flows too fast for the brittle ice.

What is the typical average rate of flow for a glacier?

An average rate of a few centimeters per day (though not always steadily), which is much slower than a snail.

In continental glacial environments, what is a nunatak?

An island of bedrock or mountaintop that protrudes above an ice sheet or ice cap.

What are the four primary glacier categories sorted in descending order of size?

1. Ice sheet (continental glacier)
2. Icecap ($\le 50{,}000\,\text{km}^2$)
3. Ice field (topography evident, such as nunataks)
4. Alpine glaciers (various types found in mountainous areas)

What are the only three ice sheets in the world, and what percentage of Earth's ice do they hold?

The East Antarctic Ice Sheet, West Antarctic Ice Sheet, and Greenland Ice Sheet; together they contain over $99\%$ of all ice on Earth.

What is an ice shelf, and what type of iceberg does it produce when it calves?

An ice shelf is a portion of an ice sheet or outlet glacier that extends floating over the ocean; it calves tabular icebergs.

What is an outlet glacier?

A glacier that flows out from an ice sheet or ice cap through a constricted valley, typically draining into the ocean.

What are the four types of alpine glaciers listed in ascending order of scale/extent?

1. Cirque glacier: forms at the head of a valley
2. Valley glacier: occupies a mountain valley
3. Piedmont glacier: lobe of ice that forms when a valley glacier flows onto a flat plain
4. Ice cap: dome of ice covering an extent of $50{,}000\,\text{km}^2$ ($19{,}300\,\text{mi}^2$) or less atop a high mountain region

What is a tidewater glacier?

A valley glacier that flows all the way to reach the sea.

What is the largest piedmont glacier in the world?

Malaspina Glacier in Alaska.

What is ablation, and what are its three physical mechanisms?

Ablation is the loss of ice from a glacier by any means:

• Calving: $\text{solid} \rightarrow \text{solid}$ (pieces break off; forms icebergs in water)
• Melting: $\text{solid} \rightarrow \text{liquid}$
• Sublimation: $\text{solid} \rightarrow \text{gas}$ (ice shifts directly to water vapor)

How is glacial mass balance formulated, and how does its sign indicate glacial advance or retreat?

$$\text{Mass balance} = \text{Accumulation} - \text{Ablation}$$

• Positive sign ($\text{Accumulation} > \text{Ablation}$): Glacial advance (forward/downslope movement of the toe)
• Negative sign ($\text{Ablation} > \text{Accumulation}$): Glacial retreat (upslope movement of the toe)

In which direction does internal ice within a glacier move when the toe of the glacier is in retreat?

Ice within a glacier is always flowing downslope, even when the toe is retreating upslope.

What is the equilibrium line on a glacier?

The transition boundary on a glacier between the zone of accumulation (where ice gain exceeds ice loss) and the zone of ablation (where ice loss exceeds accumulation).

What is the difference between glacial plucking and glacial abrasion?

Plucking is the process where a glacier pulls up and breaks off fractured pieces of bedrock as it flows downslope; abrasion is the mechanical scouring and grinding of bedrock by rock fragments embedded in the glacier's base.

What are glacial striations, glacial flour, and glacial polish?

• Glacial striations: linear grooves gouged into bedrock by rocks dragging at the glacier's base
• Glacial flour: rock pulverized into extremely fine powder by abrasion
• Glacial polish: a smooth, shiny, reflective bedrock surface caused by fine-level abrasion and mineral deposition

Identify the bowl-shaped depression, its mountain lake, and the steep headwall shown in this glaciated Alaskan landscape.

The amphitheater-like bowl is a cirque (occupied by a cirque glacier), backed by a steep cirque headwall, which drains via an outlet stream into a tarn (mountain lake).

What alpine erosional landforms are labeled in this view of the Himalayas near Shivling?

A horn (steep, pyramid-shaped peak), arêtes (sharp, knife-like ridges separating adjacent valleys), a cirque headwall, and a col (a mountain pass or opening in the ridge).

How does the cross-sectional shape of a glacial valley differ from that of a stream valley?

Glacial valleys are U-shaped troughs (wide, broad, and steep-sided) because glaciers bulldoze, pluck sides, and abrade across the whole cross-section; river valleys are V-shaped because running water downcuts vertically.

What is a hanging valley, and what feature commonly forms where it meets the main valley (such as Bridalveil Fall in Yosemite)?

A hanging valley is a tributary valley left high above the main valley floor after a deeper trunk glacier cuts and shears off the confluence; a hanging valley waterfall forms where the tributary stream plunges over the cliff.

What are paternoster lakes and glacial steps?

Paternoster lakes are a sequence of small, connected lakes along a glacial valley resembling beads on a string, separated by differential drops in elevation known as glacial steps.

What is a roche moutonnée, and how does its asymmetry indicate ice flow direction?

An elongated, asymmetrical bedrock ridge. The gently sloped, smoothed side represents abrasion by incoming ice (up-glacier), while the steep, jagged side represents plucking as ice pulled away (down-glacier).

What is a fjord, and under what conditions did fjords originally form?

A fjord is a steep-sided, U-shaped coastal glacial valley flooded by seawater. They formed during the last ice age when global sea levels were lower and glaciers carved bedrock deep below modern sea level before melting.

What is glacial drift, and how do till and fluvial sediments differ in sorting?

Glacial drift encompasses all deposits related to glaciers and meltwater streams. Till is unsorted (jumbled particles of all sizes deposited directly by ice without running water), whereas fluvial deposits are sorted by grain size by moving water.

What is a glacial erratic?

A large boulder transported by glacial ice that does not match the local bedrock where it was deposited, such as Glenstone Rock in Sweden.

What are the four primary types of glacial moraines?

• Lateral moraine: forms along the sides of a glacier
• Medial moraine: forms within the interior of a valley glacier where two lateral moraines merge
• Terminal moraine: marks the farthest downslope advance of a glacier's toe
• Recessional moraine: a ridge of till deposited at the toe during a temporary pause in retreat

When examining a succession of recessional moraines and a terminal moraine, which moraine is the oldest?

The terminal moraine is the oldest because advancing ice destroys previous moraines; recessional moraines become progressively younger as they ascend upslope toward the current glacier toe.

What is lichenometry, and how is it used in studying moraines?

A dating method based on the slow, predictable growth rate of lichens on exposed rocks, allowing scientists to determine the age of a moraine and the duration since glacial ice receded.

What distinguishes a supraglacial stream from a subglacial stream?

A supraglacial stream flows over the upper ice surface of a glacier, whereas a subglacial stream flows through channels beneath the glacier along the bedrock interface.

What is a proglacial lake?

A lake formed at the terminus (toe) of a glacier where ice has gouged a bedrock basin or where morainal sediment dams meltwater.

What is an outwash plain, and why are its streams predominantly braided?

A flat plain of glaciofluvial sediments deposited by glacial outlet streams. Streams braid because meltwater channels are overloaded with more glacial sediment than their modest discharge can carry in a single channel.

What is a drumlin?

An elongated, streamlined hill formed when an ice sheet overrides and reshapes previously deposited glacial drift or till.

What is an esker, and by what mechanism does it form?

A long, sinuous ridge of sorted sand and gravel deposited within an ice tunnel by a subglacial meltwater stream.

In kame-and-kettle topography, what are kames and kettle lakes?

Kames are irregular mounds or small hills of sediment deposited by meltwater; kettle lakes are water-filled depressions formed when buried or isolated stagnant ice blocks melt.

What were the two major ice sheets covering northern North America during the last ice age?

The Laurentide Ice Sheet (which covered Canada and shaped the Great Lakes and Midwest) and the Cordilleran Ice Sheet (west of the Rocky Mountains).

What is a moulin, and how does it affect ice sheet velocity?

A moulin is a vertical shaft in an ice sheet through which surface meltwater plunges; this water reaches the bedrock and creates a lubricating layer (basal lubrication) that accelerates glacial flow toward the ocean.

What is the modern measured rate of global sea-level rise, and how many people live within $1\,\text{m}$ of the high-tide line?

Sea level is rising at $3.2\,\text{mm}$ ($0.13\,\text{in}$) per year; over $100\text{ million}$ people worldwide reside within $1\,\text{m}$ ($3.3\,\text{ft}$) of the high-tide line.

In a meandering river system, what happens at the cut bank versus the point bar?

Erosion occurs at the outer bank due to higher water velocity (producing a cut bank), while deposition occurs at the inner bank where water velocity slows (producing a point bar).

How does an oxbow lake form from a meandering stream?

As river meanders become increasingly pronounced, the stream cuts through the narrow neck separating adjacent bends during a flood, isolating the abandoned meander loop as an oxbow lake.

What are the three categories of sediment load carried by a fluvial stream?

1. Dissolved load: mineral ions carried in chemical solution
2. Suspended load: fine solid particles (clay, silt) kept aloft by turbulent water currents
3. Bed load: coarse sand, gravel, and boulders rolling, sliding, or saltating along the streambed

What characterizes a graded stream in fluvial geomorphology?

A graded stream is in a state of dynamic equilibrium where its slope, channel geometry, and velocity are balanced to transport exactly the sediment load supplied to it without net aggradation or degradation.

How do flash floods differ from downstream floods in terms of onset, location, and hazard?

Flash (upstream) floods occur rapidly with intense localized rainfall in upper tributary basins, featuring high velocities that make them exceptionally dangerous; downstream floods occur in lower trunk streams, inundating broad floodplains with larger water volumes over longer durations.

What primary environmental issues associated with sediment loss were highlighted by the Elwha and Klamath dam removals?

Dams block fish migration routes and trap delivered sediment, starving downstream channels and coastal beaches of sand and gravel, which alters aquatic habitats and causes coastal erosion.