Major Geomorphic Processes

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Why This Matters

Earth's surface isn't static—it's constantly being sculpted by forces that break down, move, and rebuild materials. In Earth Surface Processes, you're being tested on your ability to explain how landscapes form and why they look the way they do. That means understanding the mechanisms behind geomorphic processes: weathering versus erosion, gravity-driven versus fluid-driven transport, endogenic versus exogenic forces. These distinctions show up repeatedly in exam questions asking you to compare landforms or predict how landscapes will change over time.

The processes covered here connect directly to larger course themes like landscape evolution, hazard assessment, and human-environment interactions. When you see a U-shaped valley or a coastal cliff, you should immediately recognize the process responsible and the conditions that created it. Don't just memorize definitions—know what agent of change drives each process, what landforms result, and how human activities modify natural systems.

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Breakdown and Preparation: Weathering

Weathering is the essential first step in landscape change—it prepares rock for transport by breaking it into smaller pieces or altering its chemistry. No weathering means no sediment supply for all the erosional processes that follow.

Weathering

• Breaks down rock in place—unlike erosion, weathering doesn't transport material; it simply weakens and fragments rock at the surface
• Three mechanisms operate simultaneously: physical (frost wedging, thermal expansion), chemical (dissolution, oxidation), and biological (root growth, burrowing organisms)
• Climate controls weathering type—chemical weathering dominates in warm, wet environments while physical weathering prevails in cold or arid regions

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Gravity-Driven Processes: Mass Wasting

When gravity alone moves material downslope without a transporting medium like water or wind, that's mass wasting. The steeper the slope and the more saturated the material, the greater the likelihood of failure.

Mass Wasting

• Gravity is the sole driving force—no wind, water, or ice required, though water often acts as a trigger by adding weight and reducing friction
• Speed and material vary widely—from slow soil creep (millimeters per year) to rapid debris flows and rockfalls (meters per second)
• Human triggers are common—road cuts, deforestation, and construction destabilize slopes and increase mass wasting frequency in developed areas

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Fluid Transport: Water, Wind, and Ice

These processes share a common mechanism: a moving fluid (liquid water, air, or glacial ice) picks up sediment, transports it, and deposits it elsewhere. The energy of the fluid determines how much and how far material travels.

Fluvial Processes

• Rivers are the dominant erosional agent—globally, flowing water moves more sediment than wind, ice, and gravity combined
• Erosion and deposition create distinctive landforms—V-shaped valleys, meanders, oxbow lakes, floodplains, and deltas all result from fluvial action
• Human modification is pervasive—dams trap sediment, channelization increases velocity, and land-use changes alter runoff and sediment supply

Glacial Processes

• Ice erodes through plucking and abrasion—glaciers quarry rock from bedrock and grind surfaces smooth, leaving striations as evidence
• Distinctive landforms signal past glaciation—U-shaped valleys, cirques, arêtes, fjords, moraines, and drumlins are diagnostic features
• Glaciers store freshwater and record climate—ice cores provide paleoclimate data, and glacial melt affects global sea levels

Aeolian Processes

• Wind transports fine particles selectively—saltation moves sand-sized grains; suspension carries silt and clay (loess) over vast distances
• Arid and coastal environments dominate—dunes, deflation hollows, and ventifacts form where vegetation is sparse and sediment is exposed
• Human land use accelerates wind erosion—overgrazing, deforestation, and poor agricultural practices strip protective cover and promote desertification

Coastal Processes

• Waves, tides, and currents shape shorelines—wave energy erodes headlands, transports sediment alongshore, and builds depositional features
• Erosional and depositional landforms coexist—sea cliffs, wave-cut platforms, beaches, spits, barrier islands, and tombolos reflect energy distribution
• Sea-level rise intensifies coastal hazards—erosion rates increase, and human infrastructure faces growing threats from storm surge and flooding

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Endogenic Forces: Tectonic and Volcanic Processes

These processes originate from Earth's interior heat and drive large-scale landscape construction. While exogenic processes tear landscapes down, endogenic processes build them up.

Tectonic Processes

• Plate movement creates first-order landforms—mountain ranges, rift valleys, ocean basins, and continental margins all result from plate interactions
• Three boundary types produce different features—convergent (mountains, trenches), divergent (mid-ocean ridges, rifts), and transform (fault scarps, offset streams)
• Earthquakes and uplift reshape surfaces rapidly—tectonic activity creates relief that exogenic processes then erode over geologic time

Volcanic Processes

• Magma composition controls eruption style—low-viscosity basaltic eruptions build shield volcanoes; high-viscosity silicic eruptions create explosive stratovolcanoes
• Volcanic landforms vary dramatically—calderas, lava plateaus, cinder cones, and volcanic islands each reflect different eruptive histories
• Eruptions impact climate and ecosystems—ash and sulfur dioxide can cool global temperatures, while lava flows destroy and create new land simultaneously

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Chemical Dissolution: Karst Processes

Karst landscapes form through a specific type of chemical weathering where acidic water dissolves soluble bedrock. This is weathering taken to an extreme, creating landforms entirely through rock removal.

Karst Processes

• Dissolution of solite rock drives formation—limestone, dolomite, and gypsum dissolve when exposed to carbonic acid ($H_2CO_3$) in rainwater and soil water
• Surface and subsurface features are diagnostic—sinkholes, disappearing streams, caves, and tower karst indicate active or relict karst systems
• Groundwater vulnerability is a key concern—karst aquifers lack natural filtration, making them highly susceptible to contamination from surface pollutants

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Quick Reference Table

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Self-Check Questions

1. Which two processes are both driven by fluid transport but differ in the size of particles they can move? Explain the difference.

2. How do endogenic and exogenic processes work together to create and then modify a mountain range over time?

3. Compare fluvial and glacial valleys: what diagnostic features would you use to distinguish between them in the field?

4. If an FRQ asks you to explain why karst regions face unique groundwater management challenges, which processes and landforms would you discuss?

5. Identify three geomorphic processes that are significantly accelerated by human activities, and explain the mechanism of acceleration for each.