Hilly and mountainous terrain has a remarkable tendency to organize itself into repeating ridges and valleys. The spacing of these landform sequences, which sets the density of drainage networks and the height of mountains, depends on the competition between advective sediment transport in channels and diffusive sediment transport on hillslopes. Despite promising results from numerical models, it is unclear how climate and tectonics modulates the relative effectiveness of hillslope and channel processes in determining landscape dissection. To test controls on these fundamental landscape properties, this research will incorporate diffusive hillslope transport into an existing laboratory model for actively eroding landscapes. Our physical experiments will generate reproducible hillslope transport via sediment incorporation in needle ice on the landscape surface while channels will evolve through precipitation from sprinklers. Because the experiments will be able to isolate and manipulate rates of hillslope and channel processes, we will document landform development under a wide range of climatic and tectonic scenarios. Furthermore, as the first physical experiment to explicitly incorporate hillslope processes, this research will track the dynamics of landform adjustment, such as ridge migration and drainage capture, in a system with relevance to much of the Earth?s surface.
Previous numerical and experimental studies of climate controls on landscape evolution generally focus on how precipitation drives channel discharge and valley incision. However, climate also modulates sediment production and transport on hillslopes through changes in periglacial processes and vegetation, profoundly affecting the topographic organization of landscapes. Results from our experimental landscape will inform efforts to decode past climate signals in topography as well as predict the effect of future climate change on landscape evolution. Physical experiments are a powerful tool for outreach and science recruitment because of their ability to reduce complex, million-year-scale processes in a real-time and highly accessible fashion. The funds will also provide for the construction of an experimental landscape apparatus designed explicitly for teaching and outreach. In addition to supporting the education of a PhD student, this grant includes research experience for students from local community colleges and provides for the development of a landscape evolution seminar for undergraduates.
From the arid badlands of the Henry Mountains, Utah, to the lush uplands of the Oregon Coast Range, alternating sequences of hills and valleys constitute one of the most intriguing patterns observed on Earth. The commonality of convex, soil?mantled hillslopes and concave valley profiles is particularly remarkable given that these features are found in locales that span a broad range of tectonic and climatic conditions, including some extra-planetary surfaces. Put simply, eroding terrain has a remarkable tendency to organize itself into ridge?valley sequences that collectively define drainage basins of varying scale. Our project aims to generate natural-looking landscapes in an experimental apparatus. As it stands, existing experiments have neglected to include processes representative of hillslopes wherein soil is created and conveyed into the river channel network. The combined activity of hilslopes and channels has been reasonably identified as generating commonly observed landforms, which highlights the generality of our results. To represent hillslopes, we will use a raindrop apparatus that incorporates hundreds of needles mounted on the bottom of a box with a tank that allows for the frequency and size of the raindrops to be manipulated. When these drops impact the surface of our experimental landscape, they effectively scatter and disturb silica grains of which our experimental mountain range is composed. This impacting process has the effect of blunting or smoothing sharp edges and generating smooth, convex features. By contrast, the apparatus will also be subject to periods of low intensity, but chronic misting, which collects on the landscape surface and runs off like natural rivers and streams. Real landscapes (as well as our experimental version) are generated by the combined influence of hillslope and channel processes and the forms that result encode information about climate and tectonic forces. Our experiments will enable us to better interpret and decipher real landscapes as well as assess the forces that sculpt landscapes over hourly (rather than million year!) timescales. Thus far, we have developed an appropriate experimental means to represent hillslope processes whereas the channel forming processes have been previously used in experiments for decades. In the coming year, we will conduct numerous experiments to determine how climate properties and sediment transport rates might be connected and reflected in landscape morphology.
