Thursday, June 26, 2014

Update - West Salt Creek Landslide - One month post landslide

Activities through June 26, 2014

One month following the massive West Salt Creek Landslide, Mesa County operations commander, Peter Baier, is pleased to provide the following updates and information on the monitoring activities related to the West Salt Creek Landslide.

The landslide area remains closed to the public. US Forest Service on Tuesday confirmed the closure order remains in place for USFS property around the landslide area. (The landslide began on USFS property.) The other property surrounding the landslide area is Private Property.

Please do not trespass on private property, and please respect closure of USFS access.

There are no new concerns.  Mesa County experts and others continue working to understand what happened and to learn the depth and volume of the landslide area. What we have before us is a whole new landform. So literally, experts observe “the new lay of the land” every day. Eight monitoring devices are installed, to watch the slide area. A map showing where these devices are installed, in relation to the landslide, is provided with this release. We also have received LIDAR based-maps from the Colorado Geological Survey (College of Earth Resource Sciences & Engineering, Colorado School of Mines).

Has there been movement of the landslide? Not significant movement. The large landslide block that fell off the top of the Mesa does not appear to be moving in a substantial way. We see some areas settling, or compressing. Rock fall occurs frequently from the rim, the area where the land broke away, which is on US Forest Service land. The area below the block, where the flow of mud occurred, is drying out, and compressing.

We call the landslide area dynamic. We also say the area is unstable, not necessarily because there is movement of the slide, but because it is a whole new landscape, a mix of rock, mud, sand, and broken trees. The experts say the landslide was an event that built over a 100 years or 10,000 years. We don’t know. We know it happened quickly and changed a huge amount of land form. Landslides are common on the Grand Mesa. In fact, the many ponds on the Grand Mesa were created by past landslides. What is unique about this landslide was the size. So, since this landslide occurred, we have been watching the new landform. It is not really simple to say what is ‘stable’. We know from our monitoring devices and site visits that the landslide has not shifted very much. The monitoring devices are in place, so that we can be alerted to changes to the current status.

Where are the eight monitoring devices? We include a map with this release, depicting where the monitoring devices are (“Sensor Map”).  The photo is of GPS unit 3.


What about the pond? Experts say the Pond (“sag pond” at the top of the landslide area) appears to be growing, but at a slow rate of increase. It is estimated to be the same area size that it was a week ago, which is approximately 10 acres. The level of this Pond is monitored by a pressure transducer, which sends data to USGS Water Resources and issues a warning if there is a rapid change. There has been no rapid change since the monitor was installed. A graph of the data from pond monitor is shown below.
To view similar data, please visit the National Water Information System web interface: http://waterdata.usgs.gov/co/nwis/nwisman/?site_no=09096570&agency_cd=USGS

LiDAR data and what it shows. The LiDAR information was processed by Colorado Geological Survey (CGS) and provided to Mesa County this week. A photo of the top of the landslide, based on the June 1-3, 2014 LiDAR. Courtesy: Mesa County IT/GIS and Colorado Geological Survey.

LiDAR is an acronym for “Light Detection and Ranging” which utilizes the projection of millions of laser signals to the ground from a specially equipped aircraft. The result is extremely detailed ground elevation data. The data from these LiDAR reflections are collected by measuring the time it takes for the aircraft to receive each of the millions of laser reflections. The resulting data is then combined and converted into an elevation image that looks exactly like the terrain below the aircraft, including buildings, trees, roadways, creeks, and rock outcrops. Also, using powerful software the “raw” LiDAR data can be processed to generate a number of useful end-products, including an accurate “bare-earth” terrain model in which trees, vegetation, and manmade structures have been edited out.

Colorado Geological Survey, Colorado School of Mines, prepared two posters based on LIDAR data. The first poster shows an overall LiDAR image of the landslide. https://app.box.com/s/nvv4ry8pl509hhmbk0v0. The second poster shows areas of excavation and accumulation from the landslide. https://app.box.com/s/5lszxgjxylztsd61yehw

Poster 1:“This LiDAR image of the West Salt Creek landslide was acquired June 1-3, 2014 by Quantum Spatial under the direction of the Colorado Geological Survey with funding provided by the Colorado Governor’s Office. Features as small as 3 feet across are visible. Vegetation was removed from the original data, allowing visualization of the bare ground below. The image was created by applying a simulated sun direction or hillshade effect to the original elevation dataset which enhances subtle features that may not be visible on the ground. Geologists use LiDAR for many things including mapping obscured geologic features, calculating accurate dimensions and volumes of features, generation of high-resolution slope classification maps and other derived imagery, and modeling water flow and flood inundation.” MM, Colorado Geological Survey, Colorado School of Mines.

Poster 2: “The multi-colored image is a “difference” model that shows areas of excavation (shades of blue) and accumulation (shades of red). This was created by using a computer model to subtract the surface elevations of the pre-landslide topography from the elevations of the post-landslide LiDAR dataset described above. Based on the “difference” model a calculated volume of approximately 39 million cubic yards of material was mobilized by the landslide. This is nearly 4 times the amount of material from the recent landslide near Oso, Washington.” -MM, Colorado Geological Survey, Colorado School of Mines.

Other activities. Field operations are underway for cutting trail access from the east to the west. We check and recalibrate the instruments, stake out the perimeters of the slide, so that we can measure it. We observe what is occurring in the area. We recently installed a third GPS on the top of the slide. That photo is included in this release.

We also have an advisory group of local interests impacted by the slide, and they continue to meet weekly. This meeting allows private property interests and impacted parties to ask questions, discuss concerns and make requests for assistance related to private property irrigation, fences, access, energy and related questions.

We are beginning early discussions with the property owners and others, to one day allow academic related research on this landslide. We want this effort to be coordinated to provide the utmost respect to the families of the three men who perished in this landslide, respect the property rights of the property owners and further academic research in the geology of our unique area. When more information is available concerning this goal, we will provide updates.

Information: Future media updates on this topic will be provided when conditions require. Otherwise, to view monitoring data through third party sources, please refer to the various links within this release.  Please see Mesa County government Facebook and twitter pages for many of the photos and images shown here. 

Mesa County’s webpage specific to this landslide: http://www.mesacounty.us/West-Salt-Creek-Landslide/ will also contain links to any information that may become available related to this landslide. 

For all media related inquiries, please contact Victoria Patsantaras, Mesa County Administration, 970-244-1885, or email mcadmin@mesacounty.us. Thank you.

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