Search

Landslides are geologic hazards that threaten human lives, property, and infrastructure. Effective landslide threat mitigation requires identifying, inventorying, and studying landslides; developing a detailed landslide inventory map is the beginning of this process. Here we present the first landslide inventory map of parts of the Fairbanks North Star Borough (FNSB), Alaska, along with supporting data and a qualitative analysis of the results. This research was funded by the U.S. Geological Survey (USGS) EDMAP program, which funds universities to train the next generation of geologic mappers. The map and geodatabase were developed using lidar-derived elevation data and satellite imagery, and supplemented with data from targeted fieldwork, which included field verification of landslides and a detailed field survey and series of laboratory soil tests on the large, informally named Tanana 440 landslide. We identified 1,679 landslides within the FNSB region, with 681 mapped within the focused EDMAP study area. These landslides occurred in bedrock and surficial loess deposits and vary widely in age, morphology, and material type. Most are prehistoric, but we did observe some historic and active landslides. Potential landslide triggers may include thawing permafrost, rain events, seismic events, and river erosion. Our goals with this work are to increase awareness of landslides as a potential geohazard and to aid state and local agencies and the general public in making informed land management decisions. [ABSTRACT FROM AUTHOR]

Glaciers invaded the Tyonek area several times during the Quaternary Period. Subdued Blueberry Hill drift (MIS 6?) is locally preserved near Lone Ridge, outside the limits of the Upper Chuitna moraine (MIS 4). Lack of glacial erratics on the high-level volcaniclastic plateau between Tyonek and Mount Spurr volcano and the discontinuous ring of granitic and volcanic erratics along the plateau edge that are related to the penultimate glaciation demonstrate that the volcaniclastic plateau has not been glaciated during the late Pleistocene. Below the level of the penultimate (MIS 4) glaciation, high-relief moraines of the last major (MIS 2) glaciation document ice expansions from the Capps Glacier trough, the southern Susitna Lowland, and the Chakachatna-McArthur Embayment. Comparison of till-pebble compositions supports correlation of MIS 2 moraines in the Tyonek map area with moraines of the Naptowne glaciation near Nikiski on the northwestern Kenai Peninsula. Small moraines close to modern glacier margins document minor Neoglacial and Little Ice Age glacier advances during the Holocene. Major landslides in the West Foreland (middle Eocene) and Tyonek (early Oligocene-middle Miocene) Formations are encroaching on the southwestern, northeastern, and eastern margins of the high-level volcaniclastic plateau. Physiographic relations indicate that currently active landsliding began after the last major glaciation and an older generation of landslides probably postdates the penultimate glaciation. An incipient, north-striking trellis drainage system on the volcaniclastic plateau could be evidence that the plateau is spreading. A large, mid-Holocene volcanic-debris avalanche resulted from collapse of the southern flank of the Mt. Spurr edifice. Reinterpretation of the Granite Point bluff section demonstrates that the Kaloa deposits there record subestuarine landslides and debris flows late in the last major glaciation, not evidence of multiple Miocene glaciations as previously proposed. Physiographic evidence demonstrates that the Lake Clark fault has not produced surface ruptures for at least 30 ka, probably for at least 60 ka, and possibly not for 130 ka. Physiographic and stratigraphic evidence indicates that collossal outburst flooding periodically occurred in the Beluga River during the past ~17 ka, when glacier-impounded lakes suddenly drained; massive jòkulhlaups continue to episodically inundate that drainage. Temporary damming of the Chakachatna River valley by the massive mid-Holocene volcanic-debris avalanche from the southern flank of the Mt. Spurr massif ultimately produced a massive outburst flood in that drainage. In the near future it is unlikely that another sector collapse or thickening and advance of glaciers on the southern flank of the Mt. Spurr massif will occur to dam the eastern end of Lake Chakachamna and again produce outburst flooding down the Chakachatna River. [ABSTRACT FROM AUTHOR]

The article discusses a reconnaissance rock sampling project conducted by personnel from the Alaska Division of Geological & Geophysical Surveys (DGGS) from April 30 to May 4, 2012 to obtain modern, quantitative geochemical analyses to characterize select mafic-ultramafic rocks and one chalcopyrite-bearing quartz vein sample from Yellow Hill on Annette Island, southeastern Alaska. Twenty three rock samples were collected and submitted to ALS Chemex and analyzed for ore-related trace elements.