Colorado has become synonymous with the Gold Rush of the late 1800s.
The Rockies were the perfect place for Mother Nature to create a Mother Lode.
Hard rock mining, however, is only a small part of the actual mining that has occurred throughout the Front Range.
Mining companies also discovered coal deposits in various areas around the Front Range.
They commenced coal mining operations in the late 1800's and continued mining operations until the 1920s at which time mines were abandoned.
The problem with the coal mining boom was that no one kept an accurate map of who was digging where.
We ended up with abandoned mine shafts in some pretty unlikely areas--areas which eventually became attractive to real estate developers.
There has been (and still is) extensive large-scale undermining present in our mineral rich backyard.
This has lead to a problem called subsidence.
Subsidence is simply soil sinking to fill in the voids created by the mining activities of a bygone era.
As decades-old mine support timbers and beams gradually rot away with the passing of time, gravity takes over and fills in those voids with soil from above.
The results can sometimes be sudden and dramatic to surface dwellers, their homes, and other manmade structures caught in the subsidence zone.
Why was Coal so Abundant in Colorado? Coal is the decomposed and compressed remains of primordial swamps.
It's abundant here because millions of years ago, this part of the North American Continent was covered with oceans.
As the oceans receded, fresh water swamps were formed that flourished with life.
Trees and other plant and small animal life died; decomposing and becoming peat.
Between Ice Age melting and glacial shifting, the peat became buried under tons of sand and water, which compressed under that pressure into coal.
In fact, diamonds are formed from even more pressure being applied to coal, which is why Colorado diamonds were discovered in the first place.
Due to the natural unevenness of the terrain, ribbons and fields of coal formed, which vary in depth, width, and proximity to each other.
Miners follow the ribbons of coal in an effort to find large fields of coal to excavate.
Coal in our area of the country is much sought after because it contains less sulfur than in the East-this is due to the fact that our coal is formed from fresh water swamp life, rather than saltwater! Why Does Coal Mining Lead to Subsidence? Coal is primarily mined in two ways: either surface mined or underground.
Surface mining is generally easy to detect, since the layers of earth are stripped away revealing the coal underneath.
Underground mining begins with vertical or diagonal shafts dug into the earth.
From there, horizontal tunnels called "streets" are dug until a coal seam or ribbon is discovered.
If possible, the ribbon is removed without disturbing the earth around it.
This leaves empty space where the coal used to be.
The empty spaces collapse as pressure from the surface, including the weight of a house, press down.
This is subsidence.
Ribbons of coal crisscross throughout the Front Range and as they were mined out, subsidence risks rose.
During the mining process, larger deposits of coal are found.
These areas are marked and recesses called "rooms" are created off the original tunnel.
These rooms become larger voids and are usually supported from collapse by timbers will rot away.
In some cases, vast amounts of coal are discovered in a single deposit.
It is often the result of an ancient lake or other body of water becoming completely filled with peat and turning to coal.
These are called "fields".
In order to remove a field, vast excavations occur.
This means that timber beam systems are constructed to keep the soil crust above from caving in.
During the mining process, portions of the coal, or other earth, would be left in pillars to help reduce the risk of cave in.
As the mine taps out the remaining coal in the area, these pillars are eventually removed as well and replaced with rubble, or timber.
Naturally, the pillars do not last forever.
When the soil crust above the field collapses, large areas of subsidence occur.
This subsidence usually happens quickly with dramatic results.
The signs of a shifting or subsiding foundation are not difficult to spot if you know what to look for.
The presence of any of these signs indicates that structural damage has probably already occurred in your home: --Windows and doors are sticking, hard to open --Multiple nail pops are appearing in ceilings and walls --There are large gaps in window and door frames --Window and/or door trim are developing spaces --Floors are starting to settle and become uneven --Bowed or leaning basement walls --Cracks in your foundation walls --Interior plaster walls are cracking --Chimneys are tilting or leaning --Foundations are sinking --Cracks in your basement walls If you are still concerned about subsidence, the MSIC is available to answer questions about your neighborhood's risk.
The Mine Subsidence Information Center is funded by a federal grant that was established to help residents become educated in mine subsidence concerns and remediation.
They respond, at no charge, to requests for general subsidence information from the public.
It's important to remember, though, that MSIC is a reference source and that only a qualified, independent engineer can give you an official professional opinion on the type and risk of subsidence.
This is especially important if you are entering into a real estate development, sale, or transfer.