Tom Badger. M.Sc.Project.  Adviser: Dr. Robert J. Watters The role of extensional tectonics on landsliding. Summer Lake Basin, Lake County, Oregon Summer Lake Basin is located in the northern Great Basin, a physiographic province characterized by closed, down-dropped basins and N-S mountain ranges produced by regional extension ongoing since the late Cenozoic. Summer Lake is bound on the west by Winter Rim, a 35 km long scarpment, and by Slide Mountain in the south. Pervasive, gigantic landslides dominate the nearly 1000 m high escarpments along the southwestern part of the basin. These landslides are characterized by an apparent, large rotational component within the steep bedrock escarpment and relatively long runout on the basin floor. Miocene-age basalt of andesite flows and breccias comprise the upper rim. Basin subsidence has exposed weak, underlying tuffaceous sedimentary rocks and tuffs within which landslides initiate. On the southern end of Winter rim, landslide morphology is subdued, and propagation of the range front, normal fault through the slide debris may esceed 200 m of offset. Hummocky topography and deranged drainage patterns increase northward in adjacent landslides, and fault offset within the landslide deposits diminishes. In addition to these observations, greater subsidence in the SW corner of the basin supports a theory for increasing recency of landsliding northward. Further, it suggests tha continued subsidence threatens new instability to the north in the presently stable portion of the escarpment. ^back to top

Steve Bowman. Ph. D. Project Adviser: Dr. Robert J. Watters Insights into Edifice Instability at Mount Adams, Washington (USA) Research at Mount Adams, Washington, entails investigating the geologic controls on edifice instability, including rock mass strength, discontinuity spacing and orientation, geologic structure, and the spatial distribution of hydrothermal alteration. The 1997 failures, which occurred on the west (south of the Pinnacles) and east (The Castle) sides of the volcano provide windows into the actual strength in portions of the edifice. The failures occur in regions of the edifice comprised of weak altered and unaltered rock traversed by major dominant joint sets. Inspection of the exposed sheared face below and east of the Castle summit, which acted as the failure surface of the Klickitat Glacier failure, allowed for geotechnical strength characteristics to be obtained for different portions of the failure surface. The unconfined compressive strength values from point-load testing and shear strength (cohesion and friction angle) from rock direct shear testing were obtained for the two main geotechnical units involved in the failure. The unconfined compressive strength of the main failure zone at the Klickitat failure ranged from 5.4 Mpa to 39.2 Mpa. Data from the Pinnacles area indicate unconfined rock strength from the altered andesite and scoria ranged from 10.9 Mpa to 39.7 Mpa. Three major joint sets exist at the edifice, which provide near vertical release boundaries for large fractured bounded rock masses to fail through and along a very weak lower rock mass. Preliminary stability calculations indicate continued instability of the edifice area, including the Pinnacles where pervasive hydrothermal alteration is present with the alteration of andesite rock to clay-rich soil with an andesite 'corestone' structure. Rock strength characterization of the edifice at the 1997 failure locations may permit extrapolation of the calculated strength values to other portions of the edifice with similar alteration  ^back to top

 
 

Michelle L. Broderson. M.Sc. Project DEM courtesy of Nevada Bureu of Mines (NBM) Adviser: Dr. Robert J. Watters An Engineering Analysis of Previous and Potential Shoreline Collapse in the Lake Tahoe Basin, California and Nevada. Detailed bathymetry images of the floor of the Lake Tahoe basin mapped by Gardner, et al. (1998) revealed the presence of a large landslide deposit.  Hyne, et al. (1972) proposed that the slide occurred due to instability caused by a rapid draw-down in lake level with the breaking of a glacial ice dam in the Truckee River canyon.  Alternatively, Schweickert, et al. (1999) suggested the slide was triggered by seismogenic slip events along the active faults of the West Tahoe - Dollar Point fault zone.  An engineering analysis will give more insight into the events that led to the large scale collapse in McKinney Bay.  Using strength parameters for the materials involved, both static and dynamic computer modeling will be used to interpret all probable conditions of instability in which the landslide could have occurred. The engineering stability analyses will additionally demonstrate the most likely slope failure scenario.  Stability analyses of Dollar Point and Sugar Pine Point, the shorelines adjacent to the submarine landslide scar, will assess the potential for a related, large-scale collapse in the future.  Sensitivity analyses of induced earthquake magnitude and decrease in lake level incorporated into the computer models will determine how large of a seismic event and/or amount of draw-down is needed to destabilize the slopes. ^back to top

 
 

Aline Concha-Dimas Ph.D. Project Adviser: Dr. Robert J. Watters Numerical modeling in understanding catastrophic volcanic collapse at  Citlaltepetl (Pico de Orizaba)volcano, Mexico Slope failures resulting from structural instability of andesitic volcanic edifices can generate mobile debris avalanches  that range from 0.5 to 10 km, travel as far as 100 km, and affect areas as large as 1500 km2. About 20 major volcano collapses have occurred in the past 500 years and they represent one of the most severe natural hazards for humankind. During these events more than 20,000 people have been killed (Siebert; 1984; Siebert et al.,1987) Understanding the processes of volcanic edifice failure is important as awareness of hazards in active volcanoes must be integrally recognized and evaluated.  The project proposed here has three goals: 1) Numerical modeling of previous volcanic failures to know the conditions that could trigger them; 2) Compare obtained results with actual geological conditions and volcanic activity; and 3) Predict possible future failures. A Mexican volcano with evidence of old flank collapse was chosen for this project.  Pico de Orizaba, is a dormant volcano. It has been previously modeled by Firth et al., (2000) but refinements of the models including magma injections and seismic loads are needed to complete a realistic approach to predict future possible failures. ^back to top

 

Rob Pickard. MSc Project Adviser: Dr. Robert J. Watters Rock strength and stability modeling studies of Mt. Shasta volcano, California Mt. Shasta, California rises to an elevation of 14,162 feet making it the second highest volcano in the Cascade Range.  Between approximately 300,000 and 380,000 years ago a catastrophic failure occurred on the ancestral edifice of Mt. Shasta.  The deposit from this failure covers an area of approximately 675 km2 with a volume of about 45 km3 causing it to be one of the largest Quaternary landslides known (Crandell, 1989).   The deposit forms numerous hummocks that dominate the landscape of Shasta Valley located NW of the present day volcano.  These hummocks are formed from intact blocks of the ancestral edifice and remained in place during transport.  Between the hummocks a matrix facies is found includes rip up clasts from the ancestral valley floor in addition to weaker material from the edifice, which was pulverized during transport.   This deposit is seen as a model for the type of failures that are possible today from the edifice of Mt. Shasta.  The present day Mt. Shasta is formed from four separate volcanic episodes the oldest of which is over 100,000 years old, which post dates the Shasta Valley debris avalanche deposit (Crandell, 1989).  AVIRIS data shows that each eruptive episode has corresponding areas of alteration.  Alteration of competent volcanic rock significantly decreases the strength characteristics of such altered rock.  Uniaxial compressive strength of such highly altered rock is 5.45 MPa in comparison to unaltered material with uniaxial compressive strengths of approximately 150 to 200 MPa.   Measuring discontinuity orientations within the rock mass and subsequent modeling allows the analysis of areas prone to failure, the conditions which increase the risk, the size and areas that would be affected by such failures.  The largest risk exists in the area of Shastina due to structural placement of the cone and alteration throughout the deposits.  ^back to top

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Last update: May, 2002