Outburst floods provide erodability estimates consistent with long-term landscape evolution

Abstract

Most current models for the landscape evolution over geological timescales are based on semi-empirical laws that consider riverbed incision proportional to rock erodability (dependent on lithology) and to the work performed by water flow (stream power). However, the erodability values obtained from these models are entangled with poorly known conditions of past climate and streamflow. Here we use the erosion reported for 82 outburst floods triggered by overtopping lakes as a way to estimate the outlet erodability. This avoids the common assumptions regarding past hydrology because water discharge from overtopping floods is often well constrained from geomorphological evidence along the spillway. This novel methodology yields values of erodability that show a quantitative relation to lithology similar to previous river erosion analyses, expanding the range of hydrological and temporal scales of fluvial incision models and suggesting some consistency between the mathematical formulations of long-term and catastrophic erosional mechanisms. Our results also clarify conditions leading to the runaway erosion responsible for outburst floods triggered by overtopping lakes.

Inverting Topography for Landscape Evolution Model Process Representation: 3. Determining Parameter Ranges for Select Mature Geomorphic Transport Laws and Connecting Changes in Fluvial Erodibility to Changes in Climate

“…For example, average values found in rivers eroding igneous rocks are several orders of magnitude lower than those found in rivers eroding sedimentary rocks. While not directly comparable, this result is consistent with that of Garcia‐Castellanos and O'Connor () who found a consistent relationship between lithology and erodibility and found variations of 2 orders of magnitude within lithology classes. Additionally, the variability in within a given climatic or lithologic regime is substantially less than the global range.…”

“…We thus omit from this compilation the results of Lavé and Avouac () because they present a ‐like constant in terms of excess nondimensional stress (defined below in equation ). We also omit the work of Garcia‐Castellanos and O'Connor () who present their estimates in terms of excess shear stress and focus on outburst floods. While such events can be constrained, their hydraulics differ substantially from most river systems.…”

How Lithology Impacts Global Topography, Vegetation, and Animal Biodiversity: A Global‐Scale Analysis of Mountainous Regions

“…This could suggest higher‐average erosional resistance of carbonate rocks compared to metamorphic rocks, or it may indicate that carbonate mountains are steeper due to higher rates of surface water infiltration, which can reduce discharge and stream power and therefore cause channels to steepen (Ott et al, 2019). Overall, these topographically inferred differences in erodibility are consistent with the findings from previous local‐ and regional‐scale studies (Gabet, 2020a; Garcia‐Castellanos & O'Connor, 2018; Harel et al, 2016; Kühni & Pfiffner, 2001).…”

The Geomorphic Impact of Outburst Floods: Integrating Observations and Numerical Simulations of the 2000 Yigong Flood, Eastern Himalaya

“…More information about the geometry of the Yigong landslide dam would be needed to apply breaching models using sophisticated predictive equations that involve dam dimensions (e.g., Froehlich, ). The time to peak discharge, t p , can be estimated based on the timescale of natural landslide dam failures, which varies over several orders of magnitude depending on the erodability of landslide material and failure mechanism (e.g., Garcia‐Castellanos & O'Connor, ; O'Connor & Beebee, ; Walder & O'Connor, ). Many natural landslide dams made of unconsolidated material fail by overtopping in <1 hr (Canuti et al, ; Costa, ; Costa & Schuster, ; Hewitt, ; King et al, ; Plaza‐Nieto & Zevallos, ), but dam erosion rates can also be several orders of magnitude slower, thereby producing longer breaching timescales (e.g., O'Connor & Beebee, , and references therein).…”