Climatic control of bedrock river incision

Area of Science:

• Geomorphology
• Climate Science
• Earth Surface Processes

Background:

• Bedrock river incision is fundamental to Earth's topography, mountain belt evolution, and habitability.
• Quantifying the impact of precipitation on river incision rates is challenging due to measurement difficulties and confounding factors.
• A strong dependence of river incision on precipitation has long been hypothesized but empirically difficult to establish.

Purpose of the Study:

• To empirically quantify the influence of precipitation rates on long-term bedrock river incision rates.
• To investigate the relationship between rainfall gradients and river canyon development.
• To test the hypothesis that river incision efficiency is coupled to climate.

Main Methods:

• Measurements of river incision rates were conducted across a steep rainfall gradient on Kaua'i, Hawaii.
• Long-term incision rates were inferred from river canyon depths and volcanic bedrock ages.
• An empirical law for bedrock river incision was applied, alongside numerical modeling of transient incision.

Main Results:

• A positive correlation was found between upstream-averaged mean annual precipitation rates and long-term bedrock river incision efficiency.
• Incision rates across Kaua'i demonstrated a clear dependence on precipitation, ranging from 0.5 to 9.5 meters annually.
• Measurements align with a linear relationship between river incision rates and stream power.

Conclusions:

• Precipitation rates significantly influence long-term bedrock river incision rates, providing empirical support for climate-topography coupling.
• The findings support theoretical models linking river incision to stream power and climatic drivers.
• This study offers crucial evidence for feedbacks between topography, climate, and tectonics.