My research focuses on understanding the interactions between climate, tectonics, and surface processes that drive landscape evolution. Understanding these interactions provides a key to understand how landscapes may have changed in the past and may change in the future. Below I summarize my three main research topics.
Climate & Surface processes
Climate was conventionally considered one of the crucial controls on landscape evolution, suggesting that past climate changes could alter rates of erosion and deposition. However, measuring the climatic controls on erosion rates over thousand year time-scales has been difficult. To examine climatic controls on erosion rates, I studied erosion rates and surface processes in the Washington Cascades Mountains, USA. The deglaciated Cascades is a great place to study this since it has a strong precipitation gradient with relatively uniform steep slope resulted from the last deglaciation. This study of the deglaciated Washington Cascades showed, for the first time, a strong correlation between erosion rates and mean annual precipitation. (Moon et al., 2011)
In addition, I also examine how the landscape of the Cascades might have changed since the last glacial maximum using a numerical model. The model uses geomorphic mass transport rules for processes such as landslides, river incision, and soil creep/bioturbation. By applying the numerical model to the current topography of the Cascades, I explored how the likely spatial distribution of surface processes and postglacial erosion rates might change in the future as the landscape progressively approaches a state in which tectonic and erosion rates are balanced. (Moon et al., JGR-ES, 2015)
Tectonic & Surface processes
To understand the controls of tectonics on surface processes, I studied the spatial distribution of erosion rates and surface processes in the Mendocino Triple Junction (MTJ) region in northern California. Previous studies in MTJ showed that the uplift rates inferred from marine terraces varied an order of magnitudes. In this study, I measured 10Be- and 26Al-derived erosion rates from coastal rivers, compared them with rock uplift rates from marine terraces, and examined how the landscapes including rivers and hillslopes are responding to the spatial variations of tectonic rates. (Moon et al., in prep)
I am also interested in how topography and tectonics interact to influence the spatial distribution of bedrock fractures and subsurface bedrock chemical weathering. I examined the spatial distribution of topographic stress in three sites with different tectonic stress regime. In this study, I used a boundary element model to calculate three-dimensional elastic stress fields beneath topographic surfaces, accounting for the effects of gravity and ambient tectonic stress. Then, I compared the spatial distributions of modeled failure potential with seismic velocity profiles and fractures observed in borehole image logs. This collaborative study examined how topographic stresses influence near-surface bedrock fractures, which in turn should alter patterns of weathering, erodibility, and groundwater flow. (St.Clair, Moon et al., 2015; Moon et al., 2017)
Understanding the rates and processes of chemical weathering is important since chemical weathering of silicate rocks acts as a net sink for atmospheric CO2 on geologic time scales. My work involves quantifying chemical weathering rates at catchment to global scales using river water chemistry and numerical and statistical analysis. I use a rigorous mathematical method (e.g., inverse modeling, bootstrap analysis) to quantify the rates and uncertainties of silicate weathering, and to understand the climatic and tectonic controls on chemical weathering processes.
(Moon et al., GCA, 2007; Moon et al., AG, 2009; Moon et al., GCA, 2014; Ibarra et al., GCA, 2016; Goodfellow et al., JGR-ES, 2016)