Faculty Research Highlight
We’ve had two papers published in the latest issue of Geosphere:
First, the study by Fattaruso, Cooke, and our Becky Dorsey uses 3D boundary-element models to simulate crustal deformation for different interpretations of the geometry of the southern San Andreas fault and smaller secondary faults in southern California. When compared to observed vertical motions in the Coachella Valley, Santa Rosa Mountains, and Mecca Hills, the model results suggest that this section of the fault dips steeply northeast, in contrast to existing models that assume the fault is vertical.
Fattaruso, L.A., Cooke, M.L., and Dorsey, R.J., 2014, Sensitivity of uplift patterns to dip of the San Andreas fault in the Coachella Valley, California: Geosphere, v. 10, no. 6, p. 1235–1246, URL: http://geosphere.geoscienceworld.org/content/10/6/1235.abstract.
Additionally, this study by Mackey (PhD UO 2009), and our own Sammy Castonguay, Paul Wallace, and Ray Weldon, dates the timing of normal faulting and emplacement of a lava field on the margins of ancient Fort Rock Lake. They find evidence for a period of synchronous normal faulting and dike-fed cinder cone activity about 14,000 years ago, with minimal movement since.
Mackey, B.H., Castonguay, S.R., Wallace, P.J., and Weldon, R.J., 2014, Synchronous late Pleistocene extensional faulting and basaltic volcanism at Four Craters Lava Field, central Oregon, USA: Geosphere, v. 10, no. 6, p. 1247–1254, URL: http://geosphere.geoscienceworld.org/content/10/6/1247.abstract.
In this month’s issue of Ecography, Edward Davis published a study that found a consistent mis-match between Ecological Niche Models of mammal species distributions during the Last Glacial Maximum (~20,000 years ago). This work suggests that niche models that are used to predict range shifts under future warming would be better calibrated if they also included data from Pleistocene and Holocene fossil distributions.
Davis, E.B., McGuire, J.L., and Orcutt, J.D., 2014, Ecological niche models of mammalian glacial refugia show consistent bias: Ecography, v. 37, no. 11, p. 1133–1138, URL:http://onlinelibrary.wiley.com/doi/10.1111/ecog.01294/abstract.
In that same issue, Davis has an editorial with Jenny McGuire discussing the future of conservation paleobiogography.
McGuire, J.L., and Davis, E.B., 2014, Conservation paleobiogeography: the past, present and future of species distributions: Ecography, v. 37, no. 11, p. 1092–1094, URL:http://onlinelibrary.wiley.com/doi/10.1111/ecog.01337/abstract.
Our own Gene Humphreys just published a paper in today’s issue of Nature (11/13/2014). The study is about how subduction can remove the mantle lithosphere along a continental margin, leaving it vulnerable to later tectonics and volcanism. The authors describe a type of interaction where subduction propagates along a continental margin that has a subduction zone perpendicular to the margin. Two cases are explored in this paper: the Caribbean-South America margin and the Mediterranean-Moroccan margin.
Prof. Emilie Hooft and M. Sc. Matthew Beachly investigated the magma chamber beneath Newberry volcano in central Oregon.
A 10-minute documentary for the general public explains their research
In 2008, a team of community members, undergraduate and graduate students, technicians, and scientists installed seismometers at short intervals (300 m) along a 30-km line across the volcano to record an explosion. The experiment recorded seismic waves passing around a magma chamber and later waves from energy that passed through the magma body. They combined seismic first-arrival travel-time tomography with waveform modeling of the secondary arrival to constrain the size and melt volume of the magma chamber beneath Newberry. Emilie and Garron Hale (CASIT) worked with two Digital Arts seniors, Adam Paikowsky and Hayden Steinbock, to generate the documentary.
Wherever the Earth’s surface sinks down in response to applied tectonic forces, sediments are deposited to fill the space created by subsidence. Examples of actively subsiding basins include the Ganges River plain in India, the Mississippi Delta, and the San Francisco Bay. As sediments accumulate they store a record of the local environment, depositional processes, and changing climate. Sedimentary deposits also contain a wealth of information about ancient faults, structures, and regional tectonic forces that drive basin subsidence. When sediments are later revealed by uplift and erosion, stratigraphers can extract information from the deposits to reconstruct histories of landscape evolution, climate change, and crustal deformation in tectonically active regions.
Becky Dorsey and her students use sediments to study the San Andreas fault system in southern California and NW Mexico, where it makes up the active plate boundary between the Pacific and North American plates. Because the shape of the plate boundary is highly irregular, the crust is subjected to complex deformation as the two plates grind past each other. We want to know when faults have turned on and off and how their behavior has changed through time, to help us understand controls on crustal deformation and landscape evolution. Sedimentary rocks in this region preserve a record of alternating basin subsidence and uplift over the past ~8 million years, reflecting a complex history of fault initiation, growth, and destruction.The Fish Creek – Vallecito Basin contains a remarkably well exposed record of these processes.
Basin analysis also has yielded new insights into the birth and evolution of the Colorado River. As the Pacific plate in southern and Baja California moves obliquely away from North America, this motion has opened up a deep gash, or “rupture” in the old continent that represents the early stage of a new ocean basin (see image on right). The Colorado River first entered the Salton Trough lowland about 5.3 million years ago, concluding a major integration event that completely reorganized river drainages in the Colorado Plateau region. Vigorous erosion by the Colorado River has transferred a large volume of crust from the stable continental interior to deep basins embedded in the active plate boundary over the past 5-6 million years (see related Paper). Thus we see that processes of fluvial erosion and sedimentation in this setting play a major role in regional-scale recycling of the Earth’s crust.
Do ocean currents inside Greenland’s fjords regulate the speed of mass loss from the ice sheet? What controls the onset and strength of low oxygen events in Puget Sound, WA? Though seemingly unrelated, questions like these underline the importance of understanding how coastal ocean processes can interact with estuaries prone to sensitive environmental issues, such as Greenland’s fjords or Puget Sound.
Over the last decade, observations in Greenland have shown the ice sheet to be losing an increasing amount of mass, with evidence pointing towards an ocean source as the cause. However, oceanographers’ understanding of how the fjord circulation works, which connects the outlet glaciers to the continental shelf, is extremely limited. Dr. Sutherland’sresearch is aimed at describing the processes that control the currents inside these fjords, such as Sermilik Fjord in southeast Greenland (left), by measuring water velocities, temperature and salinity (or “saltiness”) within the fjord. Dr. Sutherland and colleagues have found warm, Atlantic-origin waters penetrating the deep parts of Sermilik Fjord, which is close to 3000 feet deep (>1/2 mile!). The presence of this relatively warm water in close contact with the ice may play a role in driving glacial melt (read more).
In Puget Sound, a large fjord in Washington, coastal ocean processes also significantly impact the estuary. Puget Sound is home to millions of people in the greater Seattle area, and this population stress has been implicated in an increasing trend of hypoxic, or low-oxygen, events in some areas of the Sound. However, isolating the human effects on the Sound versus what is brought in from the coastal ocean naturally is difficult. Dr. Sutherland has developed a numerical computer model to simulate the ocean currents in Puget Sound (right) and to improve our understanding of the estuary functioning. With this tool, we aim to make predictions of what variables, such as tidal strength, winds, and/or river discharge, and what areas, such as Admiralty Inlet, affect Puget Sound the most. These predictions can help coastal managers set policy for fisheries and aquaculture, as well as aid in site identification for future tidal energy projects (read more).
If the glaciers and ice sheets that rest on top of Earth’s continents could slide away into the ocean at once, they would cause sea level to rise by several hundred feet. The terminations of ice ages have witnessed sea level changes of similar magnitudes in the past, but most current rates of flow are reassuringly glacial. Important exceptions occur on the margins of Greenland and Antarctica, where ice streams and outlet glaciers slide along at breakneck speeds of up to several miles per year past less dynamic ice ridges that stick to more normal velocities that are 100 times slower. This curious behavior is of more than simple academic interest. The most recent IPCC report emphasizes that projections for future sea level rise have no representation of ice stream behavior beyond the naive expectation that they will simply continue to behave in the same way as is seen today, no matter how the conditions that surround them change.
The ice streams sit on top of porous sediments that contain water at pressures that are almost high enough to support the entire glacier weight – almost, but thankfully not quite. A small, but important part of the load is supported instead by intermolecular forces that act between the ice and the sediment grains themselves so that friction can help to resist even more rapid sliding. In a recent paper published in the Journal of Geophysical Research – Earth Surface (Paper), Alan Rempel outlines a mathematical model that accounts for the microphysics of these ice–particle interactions.
The theory demonstrates how the same forces that cause needles of ice to grow and lift up bark mulch and small clumps of dirt at the Earth’s surface (see photo above and to the right) are instrumental in determining the fraction of ice stream weight that keeps them from flotation and firmly grounded on a layer of till instead. Further work is underway to examine how variations in the overall level of till support produce thick fringes of partially frozen till (see graph to the left) that might mark the boundaries between ice streaming regions and the more stagnant ridges alongside.