Official Stuff
This Earthcache is hidden in Hurricane Shoals Park. Permission has been granted by the County Manager. The park is NOT open year-round. Please obey all posted times. As of 3/8/2020, here are the hours*
- January-February: PARK CLOSED
- March: Open Saturdays and Sundays, 10 AM to 6 PM
- April: Open Daily 10 AM to 8 PM
- May 1st- Labor Day: Daily 9 AM to 9 PM
- September - October: Friday, Saturday, and Sunday 10 AM to 8 PM
- November-December: PARK CLOSED
*Note hours are subject to change. Please obey all posted hours
This Cache!!
This is an Earthcache! There is no physical cache to find/sign a log for. To receive credit for the Earthcache, please answer the questions below and provide a photo of you at the site.
Here are the questions to answer:
- As you observe the area, what two types of erosion are likely most common?
- Looking around, what do you notice about the area physically that may have contributed to additional heat buildup?
- Looking around, do you see any evidence of the previous explosion?
- Please take a picture of yourself at the cache site. Bonus points if it looks like you are worried about an explosion!
Below, you will find some additional details about the explosion that occurred here
What Happened Here?
On Monday, July 15, 1985, between 3 and 4 PM, a number of visitors to Hurricane Shoals Park were startled by a loud noise. "We were at the swings, and all of a sudden, it went 'boom' and 'boom' again and smoke came up out of the ground," said Johnette Rogers. "It wasn't a small noise. It was louder than a firecracker. It was like dynamite. It was enough to scare you." Said, Mrs. Cotton (Another person on site), "It sounded to me like thunder on the ground".
It took Rogers and some others nearby "about 10 seconds" to race to the spot. What they found was astounding.
The solid rock was split and shattered for a distance of about 15 feet and another 10-15 feet of ground was cracked as though an earthquake had occurred.
After ruling out "Indian Spirits" and any human activity, it was determined that the explosion was caused by a relatively rare geological phenomena (At least at the surface)
Why Would Rock Explode?
The rock in the Hurricane Shoals area was totally or partially melted when it was deposited millions of years ago. The thickness would average about 3 miles. That depth would put a tremendous amount of pressure on the rock near the bottom of the deposit.
Over the years, erosion would have worn the rock down to the highly compressed layers. But, the original stress is still there, and it is now at the surface. A hot day probably added enough stress to cause it to expand and shatter. It's basically the same thing as taking an ice tray from the freezer and putting it under running water.
This sudden expansion is not a foreign concept. In nearby Elberton, granite is mined, but cannot be mined effectively past a depth of more than 50-100 feet for the same reason. At that depth, the pressure is released and the marble cracks. It is far more uncommon for this feature to occur on the surface, but it is not unheard of.
Still, says Dr. Robert Carver of the Geology Department of the University of Georgia, visitors probably don't have to worry about being injured by such an incident in the future. "It's doubtful it will occur again in our lifetimes or even in the next 100 years.".
Of course, he did say "probably", so maybe watch out!!!
Types of Erosion
Since erosion was likely a factor, it's useful to look at different types of erosion. Here are the three main types of erosion:
- Water erosion: This can take a number of different forms that at its core is a result of water running over a surface. As the water runs over the surface, pieces of the surface (microscopic to larger) are moved by the water, exposing the earth beneath. Some examples of water erosion include:
- Splash: Water hits the ground, breaking up the top layer and causing individual particles to be hurled away (think of an impact crater, where debris is strewn out of the crater)
- Sheet: This is a result of shallow surface flow of water over the earth. Sometimes this can be subtle and hard to see
- Rill: Rills are shallow drainage lives less than 30cm deep. The develop when water concentrates in depressions or low points.
- Gully: These are channels greater than 30cm. Water flows will often concentrate and move additional earth away
- Tunnel: This occurs when water moves in channels beneath the surface.
- Wind erosion: When wind exceeds 20km per hour, it can carry particles of the earth along with it, causing erosion. This takes two main forms,
- Suspension: when lifts finer particles into the air (Example: dust storms)
- Saltation: when the wind lifts larger particles off the ground for short distances (Example: sand drifts)
- Mass Movement: This can be the result of gravity or previous glaical activity
Fun fact! The word "Erosion" comes form the Latin word ""rodere", which means to "gnaw"! Did you know that? That makes sense!
We hope you learned something new visiting this Earthcache site!
Sources
Thomas Toles. (1985, July 24). Ground Explodes. The Jackson Herald, pp. 1,10.
Soil erosion solutions: fact sheet 1: types of erosion. (n.d.). https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0003/255153/fact-sheet-1-types-of-erosion.pdf