Geology Reports⌕ Search

Geology topics

G. F. Wieczorek

Publications and source records attributed to G. F. Wieczorek.

32 records · Page 2Linked to original sources
USGS1997

Debris-flow hazards in areas affected by the June 27, 1995, storm in Madison County, Virginia

A severe storm on June 27, 1995 triggered hundreds of rock, debris and soil slides from the steep hillsides of Madison County, Virginia. Most of these transformed into debris flows that inundated areas downslope causing damage to structures, roads, utilities, livestock and crops. This report contains an analysis of areas susceptible to debris flows including an examination of source areas, channels and areas of deposition. These analyses are used to develop a methodology for identifying areas subject to debris-flow hazards in Madison County. The report concludes with a discussion of strategies for reducing debris-flow hazards and the long term risk of these hazards in Madison County as well as for similar areas along the eastern flank of the Blue Ridge.

Virginia↗
USGS1996

Triggering mechanisms and depositional rates of postglacial slope-movement processes in the Yosemite Valley, California

We examined information collected from 395 reports of slope-movement events during about the past 150 years in Yosemite National Park, central Sierra Nevada, California, to identify the most prevalent types of slope movements and their triggering mechanisms. Rock slides and rock falls have been more numerous than debris slides, debris flows, and miscellaneous slumps. Rock falls have produced the largest cumulative volume of deposits. About half of slope movements had unreported or unrecognized triggering events. Earthquakes and rain storms individually accounted for the greatest cumulative volumes of deposits from recognized triggers of all types of historical slope movements; snowmelt, human activities and freeze-thaw conditions accounted for only a small proportion of the volumes from reported triggers. A comparison of the historical and postglacial average annual rates of deposition from slope-movement processes in a portion of the Yosemite Valley indicates that, during the period 1851-1992, slope-movement processes have been producing about half the average rate of deposits than during the past 15,000 years.

Geomorphology↗
USGS1987

Real-time landslide warning during heavy rainfall

A real-time system for issuing warnings of landslides during major storms is being developed for the San Francisco Bay region, California. The system is based on empirical and theoretical relations between rainfall and landslide initiation, geologic determination of areas susceptible to landslides, real-time monitoring of a regional network of telemetering rain gages, and National Weather Service precipitation forecasts. This system was used to issue warnings during the storms of 12 to 21 February 1986, which produced 800 millimeters of rainfall in the region. Although analysis after the storms suggests that modifications and additional developments are needed, the system successfully predicted the times of major landslide events. It could be used as a prototype for systems in other landslide-prone regions.

California↗
USGS1986

Seismically induced landslides: current research by the US Geological Survey.

We have produced a regional seismic slope-stability map and a probabilistic prediction of landslide distribution from a postulated earthquake. For liquefaction-induced landslides, in situ measurements of seismically induced pore-water pressures have been used to establish an elastic model of pore pressure generation. -from Authors

Geologia Applicata e Idrogeologia↗
USGS1985

Map showing ground failures from the Greenville/Mount Diablo earthquake sequence of January 1980, Northern California

The Greenville/Mt. Diablo earthquake sequence of January 24-26, 1980, was composed of Small and moderate earthquakes; the two largest shocks, on January 24 and 26, were of magnitudes (M) 5.5 and 5.6, respectively (Bolt and others, 1981). A 5.5 event is at the lower end of the range of earthquake magnitudes which cause observable ground failure (Youd and Perkins, 1978; Keefer, 1984). While none of the slope failures produced by the Greenville/Mt. Diablo earthquake sequence (GMDES) was larger than a few tens of cubic meters, they were both widespread in area (see map) and rich in variety, and thus have much to teach us about seismically induced slope failures in the San Francisco Bay area. This map depicts the location, type, and relative size of the ground failures observed during our reconnaissance, which began at 2:30 pm PST on January 24 and continued on January 25, 26, and 28 and February 6. Our observations were generally limited to that part of the Livermore region that is accessible by state and county roads. Information about the individual ground failures may be obtained from the map and the brief descriptions in table 1. The following text is a general discussion of the distribution and the mechanisms of the ground failures, followed by a discussion of the effects of wet winter conditions and of topographic amplification on the distribution and mechanisms of slope failure, and it concludes with a description of our (unsuccessful) efforts to locate any ground failures due to liquefaction. The discussion is intended not only to describe the GMDES slope failures but also to place them into the larger general context of seismically induced slope failures.

California↗
USGS1982

Geotechnical properties of ash deposits near Hilo, Hawaii

Two holes were hand augered and sampled in ash deposits near Hilo, Hawaii. Color, water content and sensitivity of the ash were measured in the field. The ash alternated between reddish brown and dark reddish brown in color and had water contents as high as 392%. A downhole vane shear device measured sensitivities as high as 6.9. A series of laboratory tests including grain size distribution, Atterberg limits, X-ray diffraction analysis, total carbon determination, vane shear, direct shear and triaxial tests were performed to determine the composition and geotechnical properties of the ash. The ash is very fine grained, highly plastic and composed mostly of gibbsite and amorphous material presumably allophane. The ash has a high angle of internal friction ranging from 40-43? and is classified as medium to very sensitive. A series of different ash layers was distinguished on the basis of plasticity and other geotechnical properties. Sensitivity may be due to a metastable fabric, cementation, leaching, high organic content, and thixotropy. The sensitivity of the volcanic ash deposits near Hilo is consistent with documented slope instability during earthquakes in Hawaii. The high angles of internal friction and cementation permit very steep slopes under static conditions. However, because of high sensitivity of the ash, these slopes are particularly susceptible to seismically-induced landsliding.

Open-File Report↗