Principal Investigator J Perron
Landscapes on Earth and other planets contain strikingly regular patterns at scales ranging from a few centimeters to hundreds of kilometers. By studying how these topographic patterns emerge from the processes that shape a landscape, we can learn how landscapes record the major factors that shape a planet's surface over time, including bedrock geology, tectonics, climate, and life. Here is an overview of recent projects focused on specific landscape patterns:
(*) Patterns in river networks -- River networks are among the most widespread and recognizable erosional landforms on Earth. In addition to transporting water and sediment across the continents, drainage networks develop characteristic scales and patterns that reflect the main factors that shape landscapes. Our aim is to understand the origin and evolution of these patterns. Taylor Perron, graduate student Paul Richardson, postdoc Ken Ferrier, and visiting student Mathieu Lapôtre recently showed that the familiar branching structure of tributaries at the uppermost reaches of river networks arises from two coupled instabilities in an eroding landscape, and that the size of the smallest river basins with tributaries (which varies from one landscape to the next) is a signature of the erodibility of the underlying rock and the ability of the land surface to produce runoff.
River networks also create striking patterns at finer spatial scales, as they interact with hillslopes. Valleys in many landscapes are evenly spaced, like the teeth on a comb. We showed that evenly spaced valley arise through a feedback in which neighboring valleys compete for water as they erode the landscape, and that the valley spacing is a signature of the relative strengths of river incision and soil creep.
Rivers are also commonly used to reconstruct tectonic patterns in space and time. In a collaboration with Leigh Royden (MIT), we explored the application of analytical solutions for the transient evolution of river elevation profiles to the reconstruction of a landscape's tectonic history. Our analysis shows that a river's elevation profile does not necessarily preserve a complete record of its uplift history, and provides a means of quantifying how much of that information may have been lost. In a separate paper, we show how a procedure for river profile analysis based on our analytical approach improves on conventional techniques.
(*) Patterns in bedforms -- Bedforms created by wave-generated oscillatory flows are a widespread and visually striking signature of the interaction of complex flows, sediment transport, and bed topography. Postdoc Justin Kao, graduate student Kim Huppert, and undergraduate Abby Koss are collaborating with Paul Myrow (Colorado College) to compare field-scale experiments in a laboratory wave tank with numerical experiments to understand how irregular patterns (defects) in rippled beds accommodate the adjustment of bedforms to changes in the driving flow. We have found that ripples develop characteristic defects that record whether their spacing is widening or narrowing, and that these defects are commonly observed in the rock record.
We are also working to develop a new model of bedform evolution that accounts for how upstream and downstream bed topography can influence the flow stress and sediment transport at a given point. Such effects are critically important in systems in which bedform patterns are controlled primarily by length scales in the flow, such as the length of the excursion in an oscillatory flow.