Our group approaches a wide range of research questions with a variety of laboratory measurements, field work, and numerical modeling.
How does climate affect how quickly topography evolves?
Earth’s topography evolves as rock and sediment move from one place to another. The rate at which this happens is hugely variable in time and space, with some landscapes eroding hundreds of thousands of times faster than others. We use a variety of tools to investigate why this is, including measurements of the cosmogenic isotopes 10Be and 3He, which yield erosion rates over millennial timescales, as well as analysis of high-resolution topographic data, satellite imagery, and numerical modeling of landscape evolution.
Our work involves studying so-called natural laboratories – places with large variations in climate and minimal variations in other factors that might affect rates of landscape evolution. For instance, the Hawaiian island of Kaua‘i is home to some of the world’s largest and steepest rainfall gradients, while containing relatively small variations in rock type and rock uplift rates. Deep canyons incised into the underlying basalt have left sharp, steep ridges high above the rivers, and provide an exceptional natural laboratory for studying how climate steers the evolution of topography. Our work suggests that mean annual precipitation rates influence basin-averaged erosion rates as well as the efficiency of bedrock channel incision, and provides rare empirical support for theories about the size and asymmetry of mountain ranges.
Sea level dynamics
How does sediment affect sea level?
On decadal timescales, changes in sea level pose a serious hazard by modulating flood frequency, and on geologic timescales they steer the evolution of coastlines, marine sedimentary deposits, and continental topography. We are investigating how sea level responds to the massive redistribution of sediment during continental erosion and marine sedimentation around rivers with the world’s largest sediment fluxes. Our model simulations suggest that sediment erosion and deposition can significantly perturb rates and patterns of sea level change, and that these effects can persist for tens of thousands of years. Our investigations add a new piece of physics to our understanding of sea-level change, and imply that – at least near large rivers – modern rates of sea level change and patterns of paleo-sea level change must be interpreted in light of present and paleo sediment fluxes over the past tens of thousands of years.
What sets the rate of mineral weathering in soils?
Measuring chemical erosion rates in natural environments is important for a number of reasons: chemical weathering accelerates landscape evolution, releases solutes that provide the nutritional foundation for life, neutralizes acidic precipitation, and stabilizes Earth’s climate over long timescales (>100,000 years).
Steep mountains provide a natural laboratory in which to measure chemical erosion rates over a wide range of climates. Our measurements in the South Fork of the Salmon River in the Idaho Batholith show that chemical erosion rates are fastest at the highest elevations, where it is coldest and where snow cover is most persistent, suggesting that water content in soil exerts a stronger control on mineral dissolution than does temperature. Our measurements also show that mafic-rich dust has played an important role in setting soil chemistry in the Idaho Batholith, which led us to propose a novel geochemical method for inferring rates of dust incorporation into soils. Our numerical modeling suggests that soil chemical weathering fluxes should be fastest at intermediate physical erosion rates, a prediction with implications for the million-year-scale stability of Earth’s climate.