CARLSBAD — A sinkhole northeast of Carlsbad is not growing quickly, but it is still active, an expert said.George Veni, executive director of the National Cave and Karst Research Institute in Carlsbad, said aerial photographs taken this past week show very little change since the last photos were taken in October.

The sinkhole is located on state trust land about 24 miles northeast of Carlsbad approximately 17 miles southeast of Artesia on Hagerman Road (County Road 217), between County Road 206 and State Highway 360, about 100 yards north of the roadway.

Until the collapse last July, the site was the location of a brine well operated by Jim’s Water Service.

Veni, speaking Thursday at New Mexico State University’s Carlsbad campus on sink holes and what causes them, said there is a possibility that within the next 10 years, County Road 217 will have to be rerouted.

“If this sinkhole continues to grow, it will make the road unstable and subsidence could occur,” he said.

On the morning on July 18 at about 8:15 a.m. a driver for Jim’s Water Service went to the Loco Hills site to check the well. When he heard a rumbling noise in the ground, he realized something was wrong and reacted quickly to get safely away from the area.

Veni said for scientists like him, the uniqueness of this sinkhole is that it is the first one that’s formation was actually captured by seismograph equipment networking in the area.

Explaining how the sinkhole occurred, Veni said there are three types of sinkhole. The sinkhole, named “Jim’s Sinkhole,” is considered a solution sinkhole.

Solution sinkholes form where soluble bedrock such as limestone, dolomite, marble and rock salt is exposed at the land surface. This allows it to be subjected to weathering by dissolution. Surface water collects in natural depressions and slowly dissolves a sinkhole.

In brine wells, water is injected and brine water is brought back to the surface. The constant up and down action can eventually cause a collapse of the earth and the opening can grow to an enormous diameter.

Veni noted that another sinkhole in November occurred in the Lakewood area in North Eddy County, and it too, is slowly growing. It is also considered a solution sinkhole.

Veni said since the occurrence of the two solution-type sinkholes last year, the state Oil Conservation Division has tightened up and strengthened its brine well production regulations to prevent more collapses

However, the sinkhole that occurred in December south of Carlsbad near the New Mexico-Texas state line was of a different nature, he said.

He said that particular sinkhole named “Cat Sinkhole” because it swallowed a large Caterpillar tractor with its operator inside could not have been prevented.

The operator, who was unaware that he was perched on a potential sinkhole, was brought to the surface after waiting for help to arrive for more than an hour. He was 40 feet below the surface.

Veni explained that the Cat Sinkhole is considered a collapse sinkhole. It forms when surface materials suddenly sink into a subsurface cavity or cave. The cavities form slowly over time, as groundwater moves along fractures in soluble bedrock and enlarges them though dissolution.

The collapse can occur two ways: The first is when a cavity gets sufficiently large and the roof becomes too thin to support the weight of any overlying rock or sediment, so it collapses into the cavity.

The second is when caves are sometimes able to support the weight of overlying sediments because they are filled with groundwater. However, if groundwater levels are lowered, then the overlying sediment will first erode and then collapse into the de-watered cavity.

In the area of Cat Sinkhole, there are known cave formations. However, this one was unknown. Fortunately, the heavy machine landed on a ledge that stopped a further drop down into the opening.

Veni said a study of sinkhole locations in the region has been conducted and areas have been mapped where potential sinkholes could occur. Most in this area appear to be in remote locations.

 

How do sinkholes develop and enlarge?

Sinkholes are depressions or holes in the land surface. They can be shallow or deep, small or large, but all result from the dissolving of the underlying limestone. Hydrologic conditions, including lack of rainfall, lowered water levels, or conversely, excessive rainfall in a short period of time (especially after a drought), can all contribute to sinkhole development. New construction, new roads and any diversion of water flow are also common culprits.

Source: http://www.sinkholes.net/new_page_5.htm