Keith A. Labay

New Imaging of Submarine Landslides from the 1964 Earthquake Near Whittier, Alaska, and a Comparison to Failures in Other Alaskan Fjords

The 1964 Alaska M w 9.2 earthquake triggered numerous submarine slope failures in fjords of southern Alaska. These failures generated local tsunamis, such as at Whittier, where they inundated the town within 4 min of the beginning of shaking. Run-up was up to 32 m, with 13 casualties. We collected new multibeam bathymetry and high-resolution sparker seismic data in Passage Canal, and we examined bathymetry changes before and after the earthquake. The data reveal the debris flow deposit from the 1964 landslides, which covers the western 5 km of the fjord bottom. Individual blocks in the flow are up to 145-m wide and 25-m tall. Bathymetry changes show the mass transfer deposits originated from the fjord head and Whittier Creek deltas and had a volume of about 42 million m3. The 1964 deposit has an average thickness of ∼5.4 m. Beyond the debris flow, the failures likely deposited a ∼4.6-m thick megaturbidite in a distal basin. We have studied the 1964 submarine landslides in three fjords. All involved failure of the fjord-head delta. All failures eroded basin-floor sediments and incorporated them as they travelled. All the failures deposited blocks, but their size and travel distances varied greatly. We find a correlation between maximum block size and maximum tsunami run-up regardless of the volume of the slides. Lastly, the fjord’s margins were influenced by increased supply of glacial sediments during the little ice age, which along with a long interseismic interval (∼900 years) may have caused the 1964 earthquake to produce particularly numerous and large submarine landslides.

Geospatial analysis identifies critical mineral-resource potential in Alaska

Alaska consists of more than 663,000 square miles (1,717,000 square kilometers) of land—more than a sixth of the total area of the United States—and large tracts of it have not been systematically studied or sampled for mineralresource potential. Many regions of the State are known to have significant mineral-resource potential, and there are currently six operating mines in the State along with numerous active mineral exploration projects. The U.S. Geological Survey (USGS) and the Alaska Division of Geological & Geophysical Surveys (ADGGS) have developed a new geospatial tool that integrates and analyzes publicly available databases of geologic information and estimates the mineral-resource potential for critical minerals, which was recently used to evaluate Alaska. The results of the analyses highlight areas that have known mineral deposits and also reveal areas that were not previously considered to be prospective for these deposit types. These results will inform land management decisions by Federal, State, and private landholders, and will also help guide future exploration activities and scientific investigations in Alaska. For a detailed discussion of the datasets used in the analyses, explanations of the analytical process, and interpreted results of the study, see http://dx.doi.org/10.3133/ ofr20161191.

Alaska Geochemical Database - Mineral Exploration Tool for the 21st Century - PDF of presentation

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