| SCIENTIFIC CHALLENGES: TECTONICS AND CLIMATE INTERACTION
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We know the land surface evolves as tectonic forces cause deformation and as transient hydrologic and biologic forces mediate erosion and deposition on the surface. The majority of the destructive U.S. earthquakes of the last twenty years occurred on faults that did not rupture the surface, although they deformed the land surface above the fault and promoted new patterns of erosion. Interpretation of the deformed land surface allows us to construct rates of fault growth and past seismic activity. As large storms rain upon the land, topography, soils, vegetation, and rainfall intensity determine how floods and landslides are generated. We know that the amount of antecedent rainfall, soil cohesion and water content, recent fire history, water routing through the landscape, and hillslope angles all interact to determine where and when a landslide will occur. Similar interactions determine how flood waves will migrate through a catchment and how much sediment will be eroded, transported, and deposited during a storm. Remotely sensed data play an integral role in reconstructing the recent history of the land surface and in predicting hazards due to events such as floods and landslides. Because land-surface properties change through time, remote sensing of such changes yields critical time control on landscape evolution. Remotely sensed data can determine properties of the surface and atmosphere in real time and with a high spatial resolution. Recognition that destructive floods or landslides can be launched by intense, short-lived storm cells a few kilometers in width pinpoints the need for higher spatial and temporal resolution of remotely sensed data. At present, even “well monitored” river catchments commonly have only a few gauges measuring precipitation and discharge. Few data exist on soil moisture, thickness, and strength, or on vegetation cover, fire history, or detailed topography. The only practical way to gather these data is through implementation of a broad-based remote-sensing program. The height and width of rivers, as well as rainfall intensity and amounts, need to be measured hourly during storms. Developing a process-based understanding of natural hazards depends on studies of the character of previous and ongoing events. Information needed to address the challenges falls into the categories of surface, subsurface, and hydrologic characterization. These categories have diverse observational requirements. Those that change rapidly, such as river stage or precipitation, call for hourly measurements, whereas others, such as vegetation, com- monly require seasonal measurements. Occasional (5–10 yr) quantification of soil composition and thickness would suffice in areas governed by gradual processes, but more frequent measurements will be needed in areas affected by such dynamic events as flooding or landsliding. The remote sensors that will provide these data include InSAR, GPS, visible and near infrared/ thermal infrared (VNIR/TIR) imaging, multi-parameter SAR, laser altimetry, and microwave imaging. These observations will need to be augmented with extensive land-based measurements and data from existing and new hydrologic, seismologic, and geodetic arrays. By means of frequent, high-resolution remote sensing, a new capability will emerge for predicting hazards caused by tectonic–climate–land surface interactions. |
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