Coll. Res.: Tropical cyclone imprint on late Quaternary alluvial fans of Baja California: Key for understanding arid regions landscape evolution

Affiliation(s) PI Project period Funded by
DEES Antinao Rojas, Jose Luis 09/15/2011 - 08/31/2013 National Science Foundation

Project Description

The goal of the proposed project is to characterize the geomorphic response underlying alluvial fan sedimentation in the southern tip of the semiarid Baja California peninsula in Mexico, a region subjected to high intensity precipitation from tropical sources relatively isolated from other synoptic systems. The central hypothesis is that tropical cyclones have performed most of the geomorphic work during the Late Quaternary and that seasonal high intensity precipitation, coupled to rapid weathering of bedrock in this region, has generated cyclic alluvial fan aggradation in response to millennial-scale climate shifts. We propose to use cosmogenic nuclide and luminescence data supported with detailed analyses of soil chronosequence and sedimentology in the Late Pleistocene to Early Holocene alluvial units to simultaneously determine sediment production and delivery rates. Sub-hypotheses are aimed to quantitatively test sediment production and transport models widely used in arid regions of southwestern North America. For the first time, in the region of southwestern North America currently most affected by the influence of tropical circulation, its effects on Late Quaternary sediment transport will be quantified. Intellectual merit: Results will provide quantitative insights into how fast and when sediment is generated, transported and deposited in arid zone alluvial landscapes, addressing directly the program objectives of studying quantitatively coupling and feedback among processes that shape landscapes, their rates, and their relative roles. Establishing linkages between Late Quaternary synoptic patterns, especially those derived from tropical circulation, and alluvial deposition in this region might radically transform our conceptual models of arid zone landscape evolution and response to climate change, currently biased by a high-latitude climate perspective. This change will potentially prompt new hypotheses for study of other arid regions in southwestern North America, where deposition of similar alluvial fan units has occurred at times conflicting with mid-latitude proxy records. In these regions, direct observation of the effects of tropical source precipitation is not possible under the current climate, although it can be inferred from shifts in global circulation and associated synoptic patterns over millennial timescales. Improved understanding of these climate-geomorphology linkages is critical to a more precise application of arid zone alluvial fan geomorphology as a paleoclimate tool, in a relatively undeveloped research field with direct implications for global change research. Broader impacts: Expanding knowledge of arid zone alluvial fan evolution will be extremely useful in paleoseismology, paleoclimatology and paleotempestology. A more precise correlation of alluvial fans surfaces, normally used as strain markers, will improve determination of earthquake recurrence intervals and of local and regional fault slip rates, increasing our understanding of fault kinematics, not only in neighboring areas in Baja California but in all arid southwestern North America where alluvial fans can be used as chronological markers. Linkage with studies that assess activity of Eastern Pacific tropical cyclones over the last centuries and their effects on ecosystems and human population in the rapidly growing semi-arid southwestern U.S. and northwestern Mexico area will improve hazard characterization of these storms, in a global warming scenario where tropical cyclones have been suggested to strengthen. The interdisciplinary and trans-border nature of this project will reinforce collaborative ties between research institutions in Mexico and the U.S., which will include the participation of a broader but focused scientific and student audience during dissemination of the results at specific workshops. The proposed research is an integral portion of the development of a postdoctoral fellow from an underrepresented group at DRI, and will also support graduate and undergraduate student training at University of Nevada-Reno and UCLA, with substantial field and laboratory components. Further dissemination will be achieved through publications of results in peer-reviewed journals and presentations in scientific meetings.