Earth Fundamentals

My goal as an earth scientist is to understand how the natural world works, what processes are currently occurring, what has happened in the past and what we can expect for the future. The environment changes on many, many different spatial and temporal scales. Some changes are part of natural cycles, others are indisputably driven by human actions. Regardless of what is driving change, it is important to put contemporary processes into context.

Erosion is a pervasive process that drives the formation of landscapes. You can study erosion on a small scale, watching how a creek eats it's bank, removing chunks of your backyard in the process, or a regional scale, shaping the hills and valleys in eastern Pennsylvania, where I live, or on a larger scale, looking at how erosion drives the evolution of an entire mountain range or continent. It is a natural process, though in some cases humans have greatly enhanced local rates of erosion.

There are a number of ways to quantify erosion rates. Which method you use depends on the timescale you want to investigate. To study modern erosion rates, you can simply measure the sediment carried in a river. To understand how a mountain range has been eroding over million year timescales you can measure the damage trails or tracks left as a result of nuclear fission reacions in certain uranium bearing minerals (see fission track dating). Intermediate timescales, however, have proven difficult to study.

Over the past decade, a method has developed to study erosion rates over the past 10,000 to 500,000 years. This method exploits the fact that cosmic radiation, which is generated all over the universe, produces Beryllium-10 (10-Be) from Oxygen in quartz at the surface of the earth. So the amount of 10-Be in the quartz serves as a proxy for the amount of time that the quartz crystal has been at or near the surface. If there is a lot of 10-Be, it means that the quartz has been exposed at the surface for a long time, which indicates very slow rates of erosion. Little 10-Be indicates quick removal of material, or fast erosion rates.

Obtaining ~75,000,000 grains of sand in a river and subsequently measuring the amount of 10-Be in the sample allows you to infer erosion rates over 10,000 to 100,000 year time scales for the entire basin upstream from that point on the river. This method has been developed over the past decade and proven robust in many different climatic and tectonic settings, but several issues remain to be explored. Among these is a grain size dependency that has been observed in some settings, but not in others, such that larger grains (gravel or cobbles) yield faster erosion rates than do finer grains (sand). Multiple hypotheses for the generation of this grain size dependency have been proposed, but no study to date has thoroughly investigated the issue. I have identified the Clearwater River basin, western Washington state, as an ideal natural laboratory for resolving the grain size issue in tectonically active, humid settings.

The results of this study were published in Earth and Planetary Science Letters in 2007. You can download the published paper here and access all available data from my dissertation here. Contact me if you are interested in learning more about the basin-average erosion rate technique or my study in particular.


	Basin-wide erosion rates and landscape evolution in the Olympic Peninsula, western Washington State

My goal as an earth scientist is to understand how the natural world works, what processes are currently occurring, what has happened in the past and what we can expect for the future. The environment changes on many, many different spatial and temporal scales. Some changes are part of natural cycles, others are indisputably driven by human actions. Regardless of what is driving change, it is important to put contemporary processes into context. Erosion is a pervasive process that drives the formation of landscapes. You can study erosion on a small scale, watching how a creek eats it's bank, removing chunks of your backyard in the process, or a regional scale, shaping the hills and valleys in eastern Pennsylvania, where I live, or on a larger scale, looking at how erosion drives the evolution of an entire mountain range or continent. It is a natural process, though in some cases humans have greatly enhanced local rates of erosion. There are a number of ways to quantify erosion rates. Which method you use depends on the timescale you want to investigate. To study modern erosion rates, you can simply measure the sediment carried in a river. To understand how a mountain range has been eroding over million year timescales you can measure the damage trails or tracks left as a result of nuclear fission reacions in certain uranium bearing minerals (see fission track dating). Intermediate timescales, however, have proven difficult to study. Over the past decade, a method has developed to study erosion rates over the past 10,000 to 500,000 years. This method exploits the fact that cosmic radiation, which is generated all over the universe, produces Beryllium-10 (10-Be) from Oxygen in quartz at the surface of the earth. So the amount of 10-Be in the quartz serves as a proxy for the amount of time that the quartz crystal has been at or near the surface. If there is a lot of 10-Be, it means that the quartz has been exposed at the surface for a long time, which indicates very slow rates of erosion. Little 10-Be indicates quick removal of material, or fast erosion rates. Obtaining ~75,000,000 grains of sand in a river and subsequently measuring the amount of 10-Be in the sample allows you to infer erosion rates over 10,000 to 100,000 year time scales for the entire basin upstream from that point on the river. This method has been developed over the past decade and proven robust in many different climatic and tectonic settings, but several issues remain to be explored. Among these is a grain size dependency that has been observed in some settings, but not in others, such that larger grains (gravel or cobbles) yield faster erosion rates than do finer grains (sand). Multiple hypotheses for the generation of this grain size dependency have been proposed, but no study to date has thoroughly investigated the issue. I have identified the Clearwater River basin, western Washington state, as an ideal natural laboratory for resolving the grain size issue in tectonically active, humid settings. The results of this study were published in Earth and Planetary Science Letters in 2007. You can download the published paper here and access all available data from my dissertation here. Contact me if you are interested in learning more about the basin-average erosion rate technique or my study in particular.