E8 Geomorphology and Surface Processes

Topic

Geomorphology studies how the Earth's surface evolves under the combined action of tectonic uplift and the erosion triggered by that uplift. A well-established principle directly links the rate of fluvial erosion to two factors: the drainage area feeding into a specific point along the river channel—which serves as a proxy for the flow rate at that location—and the channel's slope at that same point. When erosion and tectonic uplift are perfectly balanced, the landscape reaches a steady state, maintaining its form unchanged as long as tectonic rates remain constant.

When the rate of tectonic uplift changes abruptly, the disturbance generates a wave of incision that migrates upstream from the river mouth at a characteristic speed; in large river systems, the entire landscape may take up to millions of years to fully respond to such a disturbance.

A well-established criterion also determines when river flow possesses sufficient transport capacity to move a sediment grain of a given size: below this threshold, the sediment remains stationary on the riverbed, whereas above it, the flow entrains and transports the material.

Temperature-driven chemical weathering of silicates consumes atmospheric carbon dioxide; according to a well-established hypothesis, this process acts as a long-term climate thermostat: the warmer the climate, the faster chemical weathering proceeds, and the faster it proceeds, the more atmospheric carbon dioxide it consumes, thereby mitigating the very warming that triggered it. The interaction between tectonics, climate, and erosion is bidirectional: tectonic uplift increases the erosion of the uplifted terrain, but that same erosion—along with the resulting rock exhumation—in turn affects the stress field within the Earth's crust; this modified stress field can then accelerate or retard the very tectonic uplift that triggered the erosion, thereby closing the cycle between uplift and erosion with which this description of geomorphology began.

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