Colorado has many areas susceptible to the problems that swelling soils cause. This video gives some background on the problem.
As a follow-up to our public AEG seminar last week, following are three of the PowerPoint presentations:
City of Colorado SpringsGeological Hazards Ordinance, Peter Wysocki, AICP, Planning and Community Development Director, City of Colorado Springs
Requirements for the Colorado Springs Landslide Susceptibility Zone, presented by Bob Moore, P.E., Risk Management Engineer
Landslide Susceptibility in the Colorado Springs Area – Geology and History (download), Jonathan L. White, Colorado Geological Survey
Members of our geoscience staff are busy this week participating in the Annual Meeting of the Association of Environmental & Engineering Geologists taking place in Colorado Springs this year. CGS Director and State Geologist, Karen Berry, PG, is the Technical Session Moderator, the organizer of Technical Session #18, and is hosting the annual Women in AEG/AWG Breakfast; Kevin McCoy, PhD, is a Symposium Convener and presenter; Jon Lovekin, PG, is leading the field-trip Fire, Flood, and Landslide Impacts and Mitigation around the area; CGS Deputy Director, Matthew L. Morgan presents Change Detection of the West Salt Creek Landslide, Colorado Using Multi-Temporal Lidar and UAVSAR Datasets; and Senior Engineering Geologist (Emeritus), Jon White, speaks on Landslide Susceptibility in the Colorado Springs Area — Geology and History at Technical Session #18: Landslide Hazard Info for Colorado Springs Residents and Real Estate Professionals which is a special program that is free and open to the public.
[See the AEG Annual Meeting Program/Abstracts catalog for further information.]
Kevin’s presentation, in particular, From Outcrop to Web: CGS Integrates Digital Data and GIS Technologies to Map Geology, Hazards, and Groundwater Resources, introduces some of the ground-breaking (pardon the pun!) work that we do on behalf of the citizens of the state of Colorado:
Abstract: The Colorado Geological Survey (CGS) employs an array of digital data and GIS technologies for mapping geology, natural hazards, and groundwater resources, and disseminating the resulting data to the public. Key technologies include iPads with GIS software for data collection and field verification of GIS models, a growing lidar data set for the state, digital aerial stereo imagery, GIS-based models for natural hazard analysis, GIS tools for mapping and analyzing groundwater resources, and web-based platforms for disseminating digital maps and data to the public. This talk will provide an overview of these technologies, a summary of current lidar data acquisition and statewide goals, and a summary of goals for integrating newly-emerging technologies in future projects. Two detailed case studies illustrating use of the technologies will be provided. In the County-Wide Debris Flow Susceptibility Mapping Program, CGS is mapping areas susceptible to debris flows and/or mudflows on a countywide basis for 43 counties in 13 Priority Areas comprising the mountainous portions of the state. Maps are prepared using GIS-based debris-flow source area and runout models, visual interpretation of high-resolution digital terrain data, and digitized geologic and soil survey data. In the County Geology and Groundwater Resources Program, geologists create three-dimensional layered models of geologic formations on a countywide basis in a GIS environment. This process integrates data from multiple sources starting with surface geologic maps and incorporating other datasets such as subsurface depth information, well distribution data, and water quality data. The compilation is presented in a format that allows users to visualize the spatial distribution of groundwater resources.
And the full presentation:
The city of Colorado Springs lies at the boundary between the Great Plains and the Front Range of the southern Rocky Mountains. Western sections of the city are underlain by weak claystones and shales that are prone to landslides. Several developed areas have experienced various degrees of damage from landslide movements during the 1990s and over the last several years. These landslides were widely reported in the press; however, it is apparent that significant segments of the general public are not aware that they reside in areas with landslide hazards. The purpose of this symposium is to help educate the public about the inherent risks, liabilities, and responsibilities of both living in and developing such terrain.
A free public symposium featuring a panel of experts will include informative presentations on landslide hazard risk, disclosure requirements for sellers and agents, construction requirements under the city’s revised geologic hazard ordinance, home warranties, and more.
Earthquakes strike suddenly, violently, and without warning. While Colorado is not as seismically active as some places, it does have a history of earthquake activity. Identifying potential hazards ahead of time and advance planning can reduce the dangers of serious injury or loss of life from an earthquake. Repairing deep plaster cracks in ceilings and foundations, anchoring overhead lighting fixtures to the ceiling, and following local seismic building standards, will help reduce the impact of earthquakes.
Six Ways to Plan Ahead
Nearly 100 potentially hazardous faults have been identified in Colorado. Generally, these are faults thought to have had movement within about the past 2 million years. There are other faults in the state that may have potential for producing future earthquakes. Because the occurrence of earthquakes is relatively infrequent in Colorado and the historical earthquake record is relatively short (only about 130 years), it is not possible to accurately estimate the timing or location of future dangerous earthquakes in Colorado. Nevertheless, the available seismic hazard information can provide a basis for a reasoned and prudent approach to seismic safety.
Sudden movement on long faults is responsible for large earthquakes. By studying the geologic characteristics of faults, geoscientists can often determine when the fault last moved and estimate the magnitude of the earthquake that produced the last movement. In some cases it is possible to evaluate how frequently large earthquakes occurred on a specific fault during the recent geological past.
Manitou Springs occupies a narrow valley where Fountain Creek emerges from the foothills northeast of Pikes Peak and west of Colorado Springs. The valley slopes are composed of interbedded resistant sandstone and conglomerates (i.e., gravelly sandstone), and weaker mudstones and shale. The outcropping sandstone is most prevalent on the steeper slopes on the north side of the valley.
During the wet spring of 1995, rockfall and landslides incidents increased throughout Colorado, some resulting in fatalities. In Manitou Springs, a fortunate set of circumstances occurred before the Memorial Day holiday weekend when local residents observed the movements of a large, dangerous block of rock before it actually could fall. The observation set into motion an emergency declaration by the town, resulting in a compulsory evacuation of homes located below the rocky slope, the closing of the road in the area, and an immediate rock stabilization project. During this emergency situation, the Colorado Geological Survey was asked to provide expert assistance to help stabilize the rock. The emergency evacuation decree remained in effect until the rock was stabilized and the area subsequently declared safe.
The Association of American State Geologists announced that their annual John C. Frye Memorial Award for 2017 is granted to the CGS and the staff members who authored the report The West Salt Creek Landslide: A Catastrophic Rockslide and Rock/Debris Avalanche in Mesa County, Colorado (CGS Bulletin-55). Utilizing a rich field data set, the report includes a comprehensive review of the geologic history of the area and presents a detailed timeline of the events surrounding the “the longest landslide in Colorado’s historical record.”
History of the Award:
Environmental geology has steadily risen in prominence over recent decades, and to support the growth of this important field, the Frye Award was established in 1989 by GSA and AASG. It recognizes work on environmental geology issues such as water resources, engineering geology, and hazards.
John C. Frye joined the US Geological Survey in 1938, he went to the Kansas Geological Survey in 1942, he was its Director from 1945 to 1954, he was Chief of the Illinois State Geological Survey until 1974, and was Geological Society of America Executive Director until his retirement in 1982, shortly before his death. John was active in Association of American State Geologists and on national committees, and was influential in the growth of environmental geology.
The Award is given each year to a nominated environmental geology publication published in the current year or one of the three preceding calendar years either by GSA or by a state geological survey. A shared $1000 prize and a certificate to each author is presented at the AASG Mid-Year meeting, held Tuesday morning at the GSA annual meeting.
The CGS recently installed the first of five new seismic recording stations that will collect information on seismic events around the state and the region. The CGS seismic network acts in conjunction with those maintained by the University of Colorado and Colorado State University, the Incorporated Research Institutions for Seismology (IRIS), and the US Geological Survey‘s National Earthquake Information Center (NEIC) — to provide near real-time earthquake detection. The addition of our monitoring capacity, the wider network allows the geoscience research community to better understand background seismicity in Colorado and better discriminate between natural and induced seismic events that may occur in the region.
The CGS already operates four other stations with Streckeisen STS-2 Broadband Sensors (capable of sensing ground motions over the frequency band 0.01 Hz (100 sec) to 15 Hz). They were part of a national consortium — USARRAY — that was a portable seismic network migrating around to different locations in the US several years ago. State-level organizations were allowed to ‘adopt’ some of the stations that were deployed within each state. The CGS purchased the four stations in 2010 — they are included on the map below as red boxes.
The set-up for a typical recording station includes the seismometer and its associated data recorder, a power system, and a communications system. The install site is carefully chosen for its relative acoustic silence — such that human-caused (road and air-traffic) and natural (wind, animal) noise levels are minimal at the relevant frequencies. The CGS cooperates with the Colorado State Land Board and the Colorado State Parks system in locating optimal sites for the stations in the CGS network. The particular station illustrated here is our Briggsdale Seismic Station #T25A-1 near Greeley, Colorado.
By Jill Carlson
On March 23, 2003, a large avalanche occurred about one mile west of the Town of Silver Plume. The avalanche brought trees, rock, soil and snow to the valley floor, knocked down overhead utility lines, blocked the I-70 frontage road, damaged the town’s water treatment plant (WTP), and dammed Clear Creek. The dam was breached using explosives before the plant’s electric pump motors were flooded. With damage to the WTP’s chlorine contact tank and building, Silver Plume residents had to boil their tap water for over a month.
The avalanche occurred three days after near-record snowfall. It was triggered by additional snow loading in the starting zone caused by a change in wind direction, and began in a known avalanche path above timberline on Pendleton Mountain. Its unusually large volume and velocity caused it to unexpectedly reach the valley floor, along a path not previously identified as an avalanche chute. Rick Gaubatz, the Town’s water commissioner, counted 110 rings in a spruce tree that was found in the avalanche debris at the damaged WTP, indicating that an avalanche of similar magnitude had not occurred in the immediate area in at least 110 years.
The earth’s surface can subside because of underground mining when rock is removed at depth. Although subsidence can occur due to hard rock mining, this article only considers the effects of coal mining.
When coal is extracted underground, gravity and the weight of the overlying rock may cause the layers of rock to shift and sink downward into the void left by the removal of the coal. Ultimately, this process can affect the surface, causing the ground to sag and crack and holes to form. Merely an inch of differential subsidence beneath a residential structure can cause several thousand dollars worth of damage.
Subsidence can happen suddenly and without warning. Detailed investigations of an undermined area are needed before development occurs to resolve the magnitude of the subsidence hazard and to determine if safe construction is possible. While investigations after development can determine the extent of undermining and potential subsidence, often, existing buildings cannot be protected against subsidence hazards. The cost of remedial measures is often extremely high.
The CGS’s Matt Morgan and Jon White were two of the co-authors on one of the top-ten Geological Society of America (GSA) 2016 book chapters and journal articles, this out of 600 papers. The article describes a comprehensive forensic analysis of the massive West Salt Creek rock avalanche that occurred in late May 2014 in western Colorado (USA). The analysis relied on large-scale (1:1000) structural mapping accomplished via high-resolution unmanned aircraft system imagery along with seismic data generated by more than twenty stations within approximately 500 miles (800 km) of the event. The avalanche was the largest mass-movement slope failure in the historical record of Colorado: it killed three people and narrowly avoided destroying a gas wellhead.
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On solid ground — that’s how many of us think of good old, stable earth. So it’s disconcerting when the ground moves out from under us in any way.
Because of our environment, history, and geology, Colorado has conditions where ground movements can costs millions of dollars in annual property damage from repair and remediation, litigation, required investigations, and mitigation. There has been recent attention to swelling clay soils and heaving claystone bedrock, and the media has helped publicize these problems, which are predominant along the Front Range. But that’s only half the story. Geologic hazards in Colorado also include ground that sinks. Ground subsidence and soil settlement pose significant hazards in Colorado in many areas throughout the state. A variety of causes, some human-made and others inherent to the geology and geomorphology of Colorado, cause these sinking problems.
At the end of the 19th and beginning of the 20th Century, some of the first settlers of the plateau region of western Colorado along the Colorado River, and the Uncompahgre and Paonia river basins, looked to fruit crops for their livelihood. The semi-arid but moderate climate was well suited for fruit orchards once irrigation canal systems could be constructed.
But serious problems occurred when certain lands were first broken out for agriculture and wetted by irrigation. They sank, so much in places (up to four feet!) that irrigation-canal flow directions were reversed, ponding occurred, and whole orchards, newly planted with fruit trees imported by rail and wagon at considerable expense, were lost. While not understood, fruit growers and agriculturists began to recognize the hazards of sinking ground. Horticulturists with the Colorado Agricultural College and Experimental Station (the predecessor of Colorado State University) made one of the first references to collapsible soil in their 1910 publication, Fruit-Growing in Arid Regions: An Account of Approved Fruit-Growing Practices in the Inter-Mountain Country of Western United States (pdf download). They warned about sinking ground and in their chapter, Preparation of Land for Planting, made one of the first recommendations for mitigation of the hazard. They stated that when breaking out new land for fruit orchards, the fields should be flood irrigated for a suitable time to induce soil collapse, before final grading of the orchard field, irrigation channels excavation, and planting the fruit tree seedlings.
Many areas of Colorado are underlain by bedrock that is composed of evaporite minerals. Indicative of the word evaporite, these minerals were deposited during the cyclic evaporation of shallow seas that existed in central Colorado millions of years ago. As the water continued to evaporate, the remaining solution became hyperconcentrated with salts: minerals such as gypsum, anhydrite, and halite (rock salt). These minerals precipitate out of solution and accumulate in shallow nearshore basins on the bottom of the sea floor. Depending on the paleoevironment, thinly interbedded fine sandstone, mudstone, and black shales can also occur in the evaporite. Mostly Late Paleozoic and Mesozoic rock formations contain evaporite beds in Colorado. Some are thin and discontinuous — only minor beds within a rock formation. Others are massive, with evaporitic minerals many hundreds of feet thick.
Millions of years of burial, plastic deformation, mountain building, and erosion have forced the evaporite beds to the shallow subsurface and/or ground surface today. Evaporite minerals in Colorado are a valuable mining resource. Historic mining occurred throughout the state where thin gypsum beds were exposed. Active mining continues in the massive deposits near the town of Gypsum.