Aug 142017
 
Dramatic landslide headscarp threatens this structure on Constellation Drive in Skyway, Colorado Springs, Colorado, May 2017. Photo credit: Jon Lovekin, PG.

Dramatic landslide headscarp threatens this structure on Constellation Drive in Skyway, Colorado Springs, Colorado, May 2017. Photo credit: Jon Lovekin, PG.

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.

WHAT

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.

Held in conjunction with the annual meeting of the Association of Environmental and Engineering Geologists, there is no cost or preregistration requirement but seating is limited. If you wish to attend other AEG events you will need to preregister and pay a registration fee.

WHERE

Carson Room, Antlers Hotel, Downtown Colorado Springs, Colorado

WHEN

September 15, 2017, 9:00 AM – 12:00 NOON

SCHEDULE

8:45 am — Doors Open (seating is first-come-first-serve!)

9:00 am — Opening Remarks, Mayor John Suthers, City of Colorado Springs

9:20 am — Jon White, Senior Geologist, Colorado Geological Survey: Landslide Susceptibility in the Colorado Springs Area — Geology and History

10:00 am — Marcia Waters, Director of the Division of Real Estate, Colorado Department of Regulatory Agencies: Real Estate Disclosure Requirements

10:20 am — Robert Moore, Risk Management Engineer: 2-10 Home Buyers Warranty, Requirements for Colorado Springs Landslide Susceptibility Zone

10:40 am — Don Knight and Tom Strand, Council members, City of Colorado Springs: Public Policy and Landslides, Revising the City’s Geologic Hazard Ordinance

11:20 am — Peter Wysocki, City of Colorado Springs Planning Director: New Requirements for Developing in Geologic Hazard Areas

11:40 — Panel Discussion

Jul 092017
 

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

1.) Check for Hazards in the Home
  • Fasten shelves securely to walls.
  • Place large or heavy objects on lower shelves.
  • Store breakable items such as bottled foods, glass, and china in low, closed cabinets with latches.
  • Hang heavy items such as pictures and mirrors away from beds, couches, and anywhere people sit.
  • Brace overhead light fixtures.
  • Repair defective electrical wiring and leaky gas connections. These are potential fire risks.
  • Secure a water heater by strapping it to the wall studs and bolting it to the floor.
  • Repair any deep cracks in ceilings or foundations. Get expert advice if there are signs of structural defects.
  • Store weed killers, pesticides, and flammable products securely in closed cabinets with latches and on bottom shelves.
2.) Identify Safe Places Indoors and Outdoors
  • Under sturdy furniture such as a heavy desk or table.
  • Against an inside wall.
  • Away from where glass could shatter around windows, mirrors, pictures, or where heavy bookcases or other heavy furniture could fall over.
  • In the open, away from buildings, trees, telephone and electrical lines, overpasses, or elevated expressways.
3.) Educate Yourself and Family Members
  • Contact your local emergency management office or American Red Cross chapter for more information on earthquakes. Also read the “How-To Series” for information on how to protect your property from earthquakes.
  • Teach children how and when to call 9-1-1, police, or fire department and which radio station to tune to for emergency information.
  • Teach all family members how and when to turn off gas, electricity, and water.
4.) Have Disaster Supplies on Hand
  • Flashlight and extra batteries.
  • Portable battery-operated radio and extra batteries.
  • First aid kit and manual.
  • Emergency food and water.
  • Nonelectric can opener.
  • Essential medicines.
  • Cash and credit cards.
  • Sturdy shoes.
5.) Develop an Emergency Communications Plan
  • In case family members are separated from one another during an earthquake (a real possibility during the day when adults are at work and children are at school), develop a plan for reuniting after the disaster.
  • Ask an out-of-state relative or friend to serve as the “family contact.” After a disaster, it’s often easier to call long distance. Make sure everyone in the family knows the name, address, and phone number of the contact person.
6.) Help Your Community Get Ready
  • Publish a special section in your local newspaper with emergency information on earthquakes. Localize the information by printing the phone numbers of local emergency services offices, the American Red Cross, and hospitals.
  • Conduct a week-long series on locating hazards in the home.
  • Work with local emergency services and American Red Cross officials to prepare special reports for people with mobility impairments on what to do during an earthquake.
  • Provide tips on conducting earthquake drills in the home.
  • Interview representatives of the gas, electric, and water companies about shutting off utilities.
  • Work together in your community to apply your knowledge to building codes, retrofitting programs, hazard hunts, and neighborhood and family emergency plans.

What To Do During an Earthquake

Stay as safe as possible during an earthquake. Be aware that some earthquakes are actually foreshocks and a larger earthquake might occur. Minimize your movements to a few steps to a nearby safe place and stay indoors until the shaking has stopped and you are sure exiting is safe.

If indoors
  • DROP to the ground; take COVER by getting under a sturdy table or other piece of furniture; and HOLD ON until the shaking stops. If there isn’t a table or desk near you, cover your face and head with your arms and crouch in an inside corner of the building.
  • Stay away from glass, windows, outside doors and walls, and anything that could fall, such as lighting fixtures or furniture.
  • Stay in bed if you are there when the earthquake strikes. Hold on and protect your head with a pillow, unless you are under a heavy light fixture that could fall. In that case, move to the nearest safe place.
  • Use a doorway for shelter only if it is in close proximity to you and if you know it is a strongly supported, load-bearing doorway.
  • Stay inside until shaking stops and it is safe to go outside. Research has shown that most injuries occur when people inside buildings attempt to move to a different location inside the building or try to leave.
  • Be aware that the electricity may go out or the sprinkler systems or fire alarms may turn on.
  • DO NOT use the elevators.
If outdoors
  • Stay there.
  • Move away from buildings, streetlights, and utility wires.
  • Once in the open, stay there until the shaking stops. The greatest danger exists directly outside buildings, at exits, and alongside exterior walls. Many of the 120 fatalities from the 1933 Long Beach, California earthquake occurred when people ran outside of buildings only to be killed by falling debris from collapsing walls. Ground movement during an earthquake is seldom the direct cause of death or injury. Most earthquake-related casualties result from collapsing walls, flying glass, and falling objects.
If in a moving vehicle
  • Stop as quickly as safety permits and stay in the vehicle. Avoid stopping near or under buildings, trees, overpasses, and utility wires.
  • Proceed cautiously once the earthquake has stopped. Avoid roads, bridges, or ramps that might have been damaged by the earthquake
If trapped under debris
  • Do not light a match.
  • Do not move about or kick up dust.
  • Cover your mouth with a handkerchief or clothing.
  • Tap on a pipe or wall so rescuers can locate you. Use a whistle if one is available. Shout only as a last resort. Shouting can cause you to inhale dangerous amounts of dust.

What To Do After an Earthquake

  • Expect aftershocks. These secondary shockwaves are usually less violent than the main quake but can be strong enough to do additional damage to weakened structures and can occur in the first hours, days, weeks, or even months after the quake.
  • Listen to a battery-operated radio or television. Listen for the latest emergency information.
  • Use the telephone only for emergency calls.
  • Open cabinets cautiously. Beware of objects that can fall off shelves.
  • Stay away from damaged areas. Stay away unless your assistance has been specifically requested by police, fire, or relief organizations. Return home only when authorities say it is safe.
  • Be aware of possible tsunamis if you live in coastal areas. These are also known as seismic sea waves (mistakenly called “tidal waves”). When local authorities issue a tsunami warning, assume that a series of dangerous waves is on the way. Stay away from the beach.
  • Help injured or trapped persons. Remember to help your neighbors who may require special assistance such as infants, the elderly, and people with disabilities. Give first aid where appropriate. Do not move seriously injured persons unless they are in immediate danger of further injury. Call for help.
  • Clean up spilled medicines, bleaches, gasoline or other flammable liquids immediately. Leave the area if you smell gas or fumes from other chemicals.
  • Inspect the entire length of chimneys for damage. Unnoticed damage could lead to a fire.
  • Inspect utilities.
  • Check for gas leaks. If you smell gas or hear blowing or hissing noise, open a window and quickly leave the building. Turn off the gas at the outside main valve if you can and call the gas company from a neighbor’s home. If you turn off the gas for any reason, it must be turned back on by a professional.
  • Look for electrical system damage. If you see sparks or broken or frayed wires, or if you smell hot insulation, turn off the electricity at the main fuse box or circuit breaker. If you have to step in water to get to the fuse box or circuit breaker, call an electrician first for advice.
  • Check for sewage and water lines damage. If you suspect sewage lines are damaged, avoid using the toilets and call a plumber. If water pipes are damaged, contact the water company and avoid using water from the tap. You can obtain safe water by melting ice cubes.

Refer to Federal Emergency Management Agency‘s earthquake preparedness web site for further information.

Jul 032017
 

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.

Faulting

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.

Geological studies in Colorado have discovered about 100 faults that moved during the Quaternary Period (past 2 million years) and could be considered potentially active. The Sangre de Cristo fault, which lies at the base of the Sangre de Cristo Mountains along the eastern edge of the San Luis Valley, and the Sawatch fault, which runs along the eastern margin of the Sawatch Range, are two prominent and potentially active faults in Colorado. However, not all of Colorado’s potentially active faults are in the mountains. For example, the Cheraw fault, which is in the Great Plains Physiographic Province in southeast Colorado, appears to have had multiple movements during the recent geologic past. Some potentially active faults cannot be seen at the earth’s surface. The Derby fault near Commerce City lies thousands of feet below the earth’s surface. It has not been recognized at ground level, and for that reason it is not included on the CGS Earthquake and Late Cenezoic Fault and Fold Map Server [1].

Screen-shot from the Earthquake and Late Cenezoic Fault and Fold Map Server.

Screen-shot from the Earthquake and Late Cenezoic Fault and Fold Map Server.

Several potentially active faults in Colorado are thought to be capable of causing earthquakes as large as magnitude 7.2 based on recent detailed studies. In comparison, California has hundreds of hazardous faults, one or two of which can cause earthquakes of magnitude 8.0 or larger. The time interval between large earthquakes on faults in Colorado is generally much longer than on faults in California.

Past and Possible Future Earthquakes

About 400 earthquake tremors of magnitude 2.5 or higher have been reported in Colorado since 1867. More earthquakes of magnitude 2.5 to 3.0 probably occurred during that time, but were not recorded because of the sparse distribution of population and limited instrumental coverage in much of the state. The largest known historical earthquake in Colorado occurred on November 7, 1882 and had an estimated magnitude of 6.6. The location of this earthquake probably was in the northern Front Range.

Although many of Colorado’s earthquakes occurred in mountainous regions of the state, some have been located in the western valley and plateau region or east of the mountains. The best known Colorado earthquakes were a series of events in the 1960s that were later shown to be triggered by the injection of liquid waste into a deep borehole at the Rocky Mountain Arsenal. Twelve of the so-called “Arsenal” earthquakes caused damage, including a magnitude 5.3 earthquake on August 9, 1967 that resulted in more than a million dollars in damage in Denver and the northern suburbs. This series of earthquakes continued for about ten years and was followed by about six years of quiescence. Earthquake activity resumed in the northeast Denver area in 1978, including a magnitude 4.3 event on April 2, 1981.

Colorado’s earthquake hazard is similar to other states in the intermountain west region. It is less than in states like California, Nevada, Washington, and Oregon, but greater than many states in the central and eastern United States. It is prudent to expect future earthquakes as large as magnitude 6.6, the largest historical event in Colorado.

Conclusions and Recommendations

Based on Colorado’s historical earthquake record and geologic studies, an event as large as magnitude 6.5 to 7.2 could occur somewhere in the state. Scientists are unable to accurately predict when the next major earthquake will take place in Colorado; only that one will occur. The major factors that prevent the prediction of the timing and location of future damaging earthquakes are the limited knowledge of potentially active faults and short historical record of earthquakes. Given Colorado’s continuing active economic growth and the accompanying expansion of population and infrastructure, it is prudent to continue the study and analysis of earthquake hazards. Existing knowledge should be used to incorporate appropriate levels of seismic safety into building codes and practices. Seismic safety of critical facilities and vulnerable structures is especially important. Emergency response and recovery planning should consider earthquake hazards and risk. Concurrently, we should expand earthquake monitoring, geological and geophysical research, and mitigation planning and activities.

References:

[1] Kirkham, R. M., W. P. Rogers, L. Powell, M. L. Morgan, V. Matthews, and G. R. Pattyn. “Bulletin 52B – Earthquake and Late Cenezoic Fault and Fold Map Server.” Earthquake. Bulletin. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 2004.

Jun 192017
 

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 ledge of jointed sandstone along with several large displaced blocks is seen at the center of the image. Photo credit Jon White.

The ledge of jointed sandstone along with several large displaced blocks is seen at the center of the image. Photo credit Jon White.

A prominent 12-foot-thick ledge of strongly-jointed sandstone forms the rim of this slope. Two essentially vertical and intersecting joint sets produce large orthogonal sandstone blocks that are being undermined by the more easily weathered mudstone beds below the ledge. The blocks begin to topple as the underlying rock that supports them erodes, creating dangerous overhangs. At the time of discovery, this particular block had moved 5.5 feet from the back face of the sandstone ledge and tilted precariously over the next sandstone ledge below. Had the 70-ton block fallen, it would have certainly crushed a home below.

A precarious rock above Manitou Springs started to move in 1995 after a period of wet weather. As an emergency measure, high-strength steel cables were wrapped around the rock and anchored to the surrounding ledge to arrest the movement. Photo credit Jon White.

A precarious rock above Manitou Springs started to move in 1995 after a period of wet weather. As an emergency measure, high-strength steel cables were wrapped around the rock and anchored to the surrounding ledge to arrest the movement. Photo credit Jon White.

The extremely unstable, tilted, rock could not be removed due to the proximity of homes directly below, so high-strength steel cables were wrapped around the rock and anchored to the surrounding ledge. Once the block was safely restrained, additional cables were physically attached to the top of the block at anchor points that were cemented into drill holes to provide an additional level of support for the block and safety for the homes below.

After the rock was stabilized, additional cables were physically attached to the top of the rock block and secured to surrounding stable rock. Photo credit Jon White.

After the rock was stabilized, additional cables were physically attached to the top of the rock block and secured to surrounding stable rock. Photo credit Jon White.

May 162017
 

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.”

White, Jonathan L., Matthew L. Morgan, and Karen A. Berry. “Bulletin 55 - The West Salt Creek Landslide: A Catastrophic Rockslide and Rock/Debris Avalanche in Mesa County.” Bulletins. Golden, CO: Colorado Geological Survey, 2015. Bulletin 55.

White, Jonathan L., Matthew L. Morgan, and Karen A. Berry. “Bulletin 55 – The West Salt Creek Landslide: A Catastrophic Rockslide and Rock/Debris Avalanche in Mesa County.” Bulletins. Golden, CO: Colorado Geological Survey, 2015. Bulletin 55.

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.


Citation: White, Jonathan L., Matthew L. Morgan, and Karen A. Berry. Bulletin 55 – The West Salt Creek Landslide: A Catastrophic Rockslide and Rock/Debris Avalanche in Mesa County. Bulletins. Golden, CO: Colorado Geological Survey, 2015. Bulletin 55.
May 032017
 

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.

The physical installation of an isolated off-grid seismometer station includes the excavation of a pit for the seismometer ‘vault’ to sit in, a trench for cabling from the seismometer to the recording and power equipment, and a photo-voltaic (solar) power and data transmission tower. Adequate fencing to isolate the installation from noise and physical disturbance — in this particular case, grazing cattle — is important.

Images from the installation of our fifth seismometer station near Briggsdale, Colorado.

A seismometer is a device that can sense a wide range of ground motions or vibrations. Environmental considerations require that its underground installation be both level and thermally insulated. A sub-surface concrete pad is prepared with a glass plate embedded on the top to provide a perfectly flat platform for the seismometer to sit on. After precise leveling, the seismometer is then connected to a data recording system that is installed some distance away in a weather-proof console — again to keep possible vibrations from the tower at a minimum. The data recording box includes an A-to-D (Analog-to-Digital) converter that digitizes the signal and prepares it for transmission via the communications system.

The communications system consists of a modem and a GPS transceiver. Once recorded by the seismometer, a seismic trace is converted to a digital signal, processed and sent via the modem to a local cell tower where it is relayed first to IRIS and then on to the NEIC for correlation and display. The GPS provides a standard clock signal for data synchronization, an important factor in coordinating each individual seismic station with the wider network of stations. The IRIS website provides current near-real-time data for the Briggsdale station as well as all other stations in the network.

The power system includes a deep-cycle marine battery, and a photovoltaic panel for recharging along with a voltage inverter/charge controller to ensure a stable power supply for the data recording and communications system.

The map includes our seismic stations (totaling five as of 2017) along with others available across Colorado:

Feb 062017
 

With all the precipitation in the Rockies this year (we’re at +153% normal snowpack at the moment), we thought we would re-release a publication that highlights at least one important aspect of Colorado snowfall — that is, the significant danger of avalanches. The Snowy Torrents: Avalanche Accidents in the United States 1980-86, compiled and written by Nick Logan and Dale Atkins and illustrated with Larry Scott’s fine pencil drawings, was first published in 1996. We still have a few hard-copies available and, because of that, yes, we do charge for the PDF download. However, Larry went back and re-made the PDF from the original publication file, producing a file that is far better than the rather poor digital scan we had offered previously.

The volume details 146 oft-times harrowing stories surrounding avalanches, the lives they claim, survivors and witnesses, along with assessments as to what happened, why it happened, and what could have been done to prevent loss of life and/or property. The authors are never judgmental, and their clear-eyed accounts contain a wealth of wisdom that will add to the knowledge-base of any winter backcountry enthusiast.


Citation: Logan, Nick, and Dale Atkins. SP-39 The Snowy Torrents: Avalanche Accidents in the United States, 1980–86. Special Publications 39. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 1996.
Feb 012017
 

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.

Avalanche debris in the runout zone taken by Xcel Energy from a helicopter on the morning after the avalanche occurred, 24 March, 2003.

Avalanche debris in the runout zone taken by Xcel Energy from a helicopter on the morning after the avalanche occurred, 24 March 2003.

Continue reading »

Jan 302017
 

Introduction

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. Continue reading »

Jan 162017
 

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. Continue reading »

Jan 122017
 

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. Continue reading »

Jan 102017
 

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.

Evaporitic bedrock locations in Colorado. [Gypsum Mines from Mineral Resources of Colorado, 1968, P. 191; Geology Modified From Tweto, 1979]

Evaporitic bedrock locations in Colorado. [Gypsum Mines from MI-07 Mineral and Water Resources of Colorado, 1968, P. 191; Geology modified from Tweto, 1979]

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. Continue reading »

Apr 222016
 

Subsidence experts visiting the Netherlands. Deltares hosted 15 international subsidence experts to discuss subsidence problems worldwide at the annual meeting of UNESCO Land Subsidence working group. Gilles Erkens, subsidence expert Deltares showed the impact of subsidence in the Netherlands during a field trip.

Land subsidence is causing more and more damage every year. It scarcely registers on the radar of many countries. Even so, the impact on coastal cities and peat areas is increasingly apparent. Levels of flood damage are rising and the risk of casualties is following. Land subsidence can also lead to major economic losses such as structural damage and high maintenance costs for roads, railways, dikes, pipelines and buildings. The total bill worldwide mounts up to many billions of dollars annually. It can only rise further in the future with population growth and the intensification of economic activities in delta areas.