The western Columbia Gorge has been long recognized as an area susceptible to landslides. Abundant rainfall, steep terrain, geologic structure and erosion by the Columbia River combine to create topography capable of ground movement. Yet dense forests have hampered efforts to accurately map old and currently active landslides and to fully understand the scope of this hazard.
A new study uses lidar to map and characterize known and previously unrecognized landslides in the western Columbia Gorge, Washington. Lidar is a remote-sensing technique that provides images of terrain from which vegetation and structures can be digitally "erased" to show the underlying bare ground. Formerly hidden by forest, lidar reveals telltale landslide indicators such as scarps, cracks and ridges, slope depressions, bulges and toes.
The imagery shows that landslides cover about two thirds of the 222 square km (86 square mi) map area. Two of the largest landslides in the map area—the Bonneville and Red Bluffs landslides, averaging about 75 m (250 ft) thick with runouts of 6-7 km (~4 mi)—failed catastrophically and slid rapidly to the river within the last 600 years; the Bonneville landslide temporarily dammed the Columbia River and formed the "Bridge of the Gods" known from Native American legends.
Research shows that these landslides have complex movement histories and have been active over thousands of years; some have moved recently or are currently moving. Another such landslide rapidly sliding into the Columbia River today could have a catastrophic impact on downstream communities and on the transportation and energy-distribution infrastructure of the Pacific Northwest.
The publication, Landslides in the western Columbia Gorge, Skamania County, Washington, is available online.
Much is known about the shallow magmatic system beneath Mount St. Helens. But as you go deeper, the picture is less clear. New research suggests that temperatures 40-50 miles beneath the volcano are too cold to generate magma. Yet, Mount St. Helens is the most active in the Cascade Range, erupting catastrophically on May 18, 1980 and producing two dome-building pulses from 1980-86 and 2004-08. So where does the magma come from?
In a recent article from researchers at the University of New Mexico, Rice, University of Washington, Cornell and University of Arizona, the dataset from seismic experiments conducted in 2014 for the collaborative iMUSH program (Imaging Magma Under St. Helens) show that Mount St. Helens sits atop a cold hydrated mantle wedge (less than 1300 degrees F) produced by subduction of the oceanic plate. The temperature of the wedge is too cold to be part of the process that forms magma to feed Mount St. Helens. A primary conclusion of this article is that magma is generated somewhere to the east of the volcano, with magma at some point moving west into Mount St. Helens' magmatic system. More studies are needed to determine the lateral pathway(s) necessary for the magma to reach the shallow reservoir beneath the crater floor. Additional iMUSH results are expected to be published in the coming months.
Follow the link for more information on the eruptive history of Mount St. Helens.
Newberry is a broad shield-shaped volcano in central Oregon that rises a mile above sea level. It has been constructed by thousands of eruptions, including at least 25 in the last 12,000 years.
To better understand Newberry's past and assess future hazards, the USGS worked with the Oregon Department of Geology and Mineral Industries and Oregon Lidar Consortium to obtain 500 square miles of high-precision airborne lidar (Light Detection and Ranging) data at and around Newberry. These data provide a digital map of the ground surface beneath forest cover, revealing landforms with astounding clarity. The lidar-derived Digital Elevation Model (DEM) of the area also includes bathymetric surveys of East Lake and Paulina Lake.
The DEM dataset, High-resolution digital elevation dataset for Newberry Volcano and vicinity, Oregon, based on lidar survey of August-September, 2010 and bathymetric survey of June, 2001, is available online. The individual DEMs must be opened by software that can read and process GIS data. The hillshades zip file includes tifs that can be opened by an image viewer.
In the early morning hours of September 23, 2004, a swarm of small-magnitude earthquakes about half a mile below Earth's surface marked the reawakening of Mount St. Helens after 18 years of eruptive quiescence. Steam and ash explosions on October 1 were followed by three years of lava extrusion that formed a new dome inside the crater. The lava dome pushed Crater Glacier aside, causing it to flow rapidly toward the front of the 1980 breach; flow continues today.
Scientists at the USGS-Cascades Volcano Observatory and its partners used many techniques during the 2004-2008 eruption to monitor the volcano, including interpretation of seismicity, ground deformation, thermal imaging, time lapse photography and lava sampling. Because of its location, easy access, and varied styles of eruptions, Mount St. Helens has become our 'go-to' volcano for development and testing of monitoring devices and techniques. Lessons learned at Mount St. Helens have been shared with researchers around the world to better understand volcano behavior, assess hazards and potential impacts, and provide timely warnings of future events.Read more in USGS Professional Paper 1750, chronicling the renewed eruption of Mount St. Helens (2004-2006). Follow the link for a brief recap of 2004-2008 events.