RFG 2018 Conference


Catastrophic debris flows transformed from landslides in volcanic terrains : mobility, hazard assessment and mitigation strategies

Communities in lowlands near volcanoes are vulnerable to significant volcanic flow hazards in addition to those associated directly with eruptions. The largest such risk is from debris flows beginning as volcanic landslides, with the potential to travel over 100 kilometers. Stratovolcanic edifices commonly are hydrothermal aquifers composed of unstable, altered rock forming steep slopes at high altitudes, and the terrain surrounding them is commonly mantled by readily mobilized, weathered airfall and ashflow deposits. We propose that volcano hazard assessments integrate the potential for unanticipated debris flows with, at active volcanoes, the greater but more predictable potential of magmatically triggered flows. This proposal reinforces the already powerful arguments for minimizing populations in potential flow pathways below both active and selected inactive volcanoes. It also addresses the potential for volcano flank collapse to occur with instability early in a magmatic episode, as well as the 'false-alarm problem'-the difficulty in evacuating the potential paths of these large mobile flows.

Stability of natural slopes in the Presumpscot Formation

Identification of landslide prone sites in Maine is imperative in order to maintain the safety of affected developed areas and future developments. Large landslides in Gorham, Maine in 1983 and Rockland, Maine in 1973, a number of smaller landslides, and evidence of historical and prehistorical landslides indicate that some areas of Maine, including developed areas will be susceptible to future landslides. Past landslides have occurred in deposits of the sensitive glaciomarine clay known as the Presumpscot Formation which covers the populated and rapidly developing eastern and southern Maine.

Landslides in the Presumpscot Formation: An engineering study

Many landslides in Maine have occurred in the marine clay, called the Presumpscot Formation, which covers much of southern Maine. This glacially derived clay was deposited in the sea during the retreat of the late Wisconsinan ice sheet, and subsequently was uplifted by crustal rebound after the glacier receded. Most of the landslides are single rotational slides, but some of them comprise a number of slides formed by retrogressive slope failure. The retrogressive slides are potentially the most destructive, since they occur rapidly with little apparent warning and cover a large area.

Inventory and bibliography of Maine landslides

A survey conducted by the Maine Geological Survey has provided information on recent and historical slides throughout the State of Maine (see Plate 1, Landslides in Maine). The landslide inventory questionnaire (Figure 1) was distributed to nearly 1,000 geologists, soil scientists, site evaluators, civil engineers, and public works directors. The location, date of occurrence (if known), slide type, size, material involved, and extent of damage for 50 failures has been compiled from the returned forms (Table 1).

Geologic, geotechnical, and geophysical investigation of a shallow landslide, eastern Kentucky

In eastern Kentucky, landslides occur in colluvial soils or at the colluvium-bedrock contact, and are commonly triggered by heavy rainfall. These slides occur particularly where steep slopes and weak rocks combine with various methods of slope modification. Landslides can damage roadways, infrastructure, and residences, and mitigation costs can exceed $10 million per year. The Meadowview landslide in Boyd County was investigated to assess the geologic conditions, extent, and behavior of a rainfall-triggered landslide in eastern Kentucky and evaluate the use of electrical resistivity as a tool to characterize a shallow colluvial landslide.

Kentucky Geological Survey landslide inventory: From design to application

The Kentucky Geological Survey is compiling a landslide inventory database to better document the distribution and geologic context of Kentucky’s landslides. The database provides users with easy access to landslide information, raises awareness of landslide causes, and will help prevent property damage or injury. The database was used to create an online landslide information map, which provides online access to landslide data and gives users the ability to customize the map using other data layers pertinent to landslides. The database design is based on common attributes collected by other states with active inventories and landslide hazard programs, as well as attributes necessary to document landslides in Kentucky and help with future research goals. A comprehensive landslide inventory database serves as a foundation for understanding landslide distribution, assisting land-use planning decisions, creating hazard maps, and modeling landslide susceptibility.

Interactive map of geohazards in Oregon

The Oregon Department of Geology and Mineral Industries statewide geohazard viewer, HazVu, provides a way to view a range of geohazards in the state of Oregon,including:

  • Earthquakes - active faults, historical epicenters, expected shaking, and liquefaction hazards
  • Tsunami inundation hazard
  • Volcanoes
  • Landslides - historical landslides and landslide susceptibility
  • Floods
  • Coastal erosion

The map also includes public buildings so that hazards can be assessed for these locations.


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