Logging Requirements
1. Find a good area to observe the sinkhole. what do you estimate the size (length and width) of the sinkhole?
2. What do you think caused the sinkhole to finally collapse?
3. In your opinion is this a cenote or sink/stream type of sinkhole? Explain your answer
4. Do you see signs of human interaction to help create this sinkhole? For example ground being disturbed by infrastructure, explain.
5. Optional:A picture of you at location would be great
HV Griffin
HV Griffin park opened in 1974 when I was 5 years old. I played baseball and football here from the time it opened and now play disc golf here more than anything else. Growing up we warmed up for baseball games close to here and there was a decent sized pond at this location. Foul balls and misdirected throws ended up in the pond and gone forever. At that age we never knew there was an underlying issue here waiting to collapse into who knows where? When we get fast and a lot of rain it fills back up but not for long. Cache is available from 5:00 AM to 11:00 pm every day. There is an older fence surrounding the sinkhole, please stay out of the fenced in area.
Karst Topography
Karst topography forms in areas where the underlying bedrock is composed of material that can be slowly dissolved by water. Examples of this type of sedimentary rock include carbonate rocks such as limestone, halite, gypsum, dolomite, and anhydrite. Carbonate rocks may develop karst and other dissolution features due to the effects of circulating groundwater that has been made slightly acidic through the presence of dissolved carbon dioxide (which creates carbonic acid that reacts with the rock, dissolving it). Sinkholes and caverns can form, creating potential hazards (i.e., the land surface could subside or collapse into the underground openings). This may principally occur in areas where cavities filled with water are emptied through groundwater withdrawal or other natural processes, resulting in the cavities being filled with air and reducing support for the overlying rock. Bedford County is surrounded in carbonite karst topography because of all the limestone and dolomite in the area. There are only a couple of mapped sinkholes in the county, mainly because they only map sinkholes greater than 100 feet deep.
Sinkholes
A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are also known as shakeholes, and to openings where surface water enters into underground passages known as ponor, swallow hole or swallet. A cenote is a type of sinkhole that exposes groundwater underneath. Sink and stream sink are more general terms for sites that drain surface water, possibly by infiltration into sediment or crumbled rock.
Most sinkholes are caused by karst processes – the chemical dissolution of carbonate rocks, collapse or suffosion processes. Sinkholes are usually circular and vary in size from tens to hundreds of meters both in diameter and depth, and vary in form from soil-lined bowls to bedrock-edged chasms. Sinkholes may form gradually or suddenly, and are found worldwide.
Sinkholes may capture surface drainage from running or standing water, but may also form in high and dry places in specific locations. Sinkholes that capture drainage can hold it in large limestone caves. These caves may drain into tributaries of larger rivers.
The formation of sinkholes involves natural processes of erosion or gradual removal of slightly soluble bedrock (such as limestone) by percolating water, the collapse of a cave roof, or a lowering of the water table. Sinkholes often form through the process of suffosion. For example, groundwater may dissolve the carbonate cement holding the sandstone particles together and then carry away the lax particles, gradually forming a void.
In a landscape where limestone sits underneath the soil, water from rainfall collects in cracks in the stone. These cracks are called joints. Slowly, as the limestone dissolves and is carried away, the joints widen until the ground above them becomes unstable and collapses. The collapse often happens very suddenly and without much warning. Water collects in these collapsed sections, forming sinkholes.
Rainfall percolating, or seeping, through the soil absorbs carbon dioxide and reacts with decaying vegetation, creating a slightly acidic water. That water moves through spaces and cracks underground, slowly dissolving limestone and creating a network of cavities and voids. As the limestone dissolves, pores and cracks are enlarged and carry even more acidic water. Sinkholes are formed when the land surface above collapses or sinks into the cavities or when surface material is carried downward into the voids.
Drought, along with resulting high groundwater withdrawals, can make conditions favorable for sinkholes to form. Also, heavy rains after droughts often cause enough pressure on the ground to create sinkholes.
Sinkholes can be triggered by human activities such as: overwithdrawal of groundwater or diverting surface water from a large area and concentrating it in a single point.
Limestone
Since most sinkholes are formed in limestone rock that must be relevant in the formation of sinkholes. Limestone is a sedimentary rock composed principally of calcium carbonate (calcite) or the double carbonate of calcium and magnesium (dolomite). It is commonly composed of tiny fossils, shell fragments and other fossilized debris. These fossils are frequently visible to the unaided eye on close examination of the stone surface, however this is not always the case. Some varieties of limestone have an extremely fine grain.Limestone is usually gray, but it may also be white, yellow or brown. It is a soft rock and is easily scratched. Since it's a softer rock it is susceptible to rain water runoff creating cavities in the rock.