The Black Hole EarthCache
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Solve the mystery of the Black Hole!
This Earthcache is located at a geological marker. Plenty of parking is available at the posted coordinates. Entrance is located on the North-bound lane of highway 371. Please take note of the logging requirements located near the bottom of the description.
The Brainerd Lakes Area was shaped by Glaciers many thousands of years ago. Glaciers are large bodies of ice formed when snow/ice accumulates faster than it can melt. When the bottom layer of ice melts, the glacier may move. This movement is what was often responsible for carving out the many lakes found in Minnesota.
"The Black Hole"
This marker is located on North Long Lake. In the early 2000's, this lake had the attention of many scientists, biologists, geologists, and even astronomers.
In the middle of the harsh Minnesota winter, a mysterious hole - measuring 2,128 feet long by 400 feet wide - opened up in the middle of the ice-covered North Long Lake. Average January temperatures for the area typically range from a high of 20 degrees F (-7 C) to a low of -5 degrees F (-20 C). More surprising is that when the temperatures warmed up to over 40 degrees, the hole froze back up. It earned the 'Black Hole' nickname after it engulfed over a dozen vehicles and even claimed a life.
The cause of this phenomenon became an instant source of speculation.
Theories ranged from distant earthquakes, new thermal springs on the lake bottom, space junk that fell into the lake, heat from light reflecting off water and windows of nearby houses, radiation, backed up septic tanks, sunken ice house warmers, illegal piping under the lake, tectonic shifts, pollution, UFOs, and a secret stash of nuclear material buried by the KGB.
Clearly, some of these were more scientific than others. Let's explore some of the more plausible possibilities.
North Long Lake lies directly on the Great Lakes Tectonic Zone. The GLTZ is a Precambrian crust that extends over 740 miles (1,200 kilometers) from Minnesota to Ontario. This area has historically had the most seismic activity in the state. It is also the most likely area for seismic activity to occur in the future. Even the slightest shifts in the tectonic plates here could cause enough friction to create thermal phenomena on a local level. The last earthquake in this region was a magnitude 2.5 that occurred near Alexandria on April 29, 2011.
This area also shares a large water table. This lake belongs to the Thirty Lakes Watershed District, which is part of the Upper Mississippi River Basin. At the time of the 'Black Hole' the area was the wettest it had been in 70 years. If the water tables were full, it could cause extra water movement. Water flowing in from lake bottoms could create currents that melt ice and snow in areas.
Divers were sent to investigate the lake bottom multiple times for any clues. They also took water samples to be tested. High levels of phosphorus were measured. Phosphorus readings typically range from 20 to 28; but on two occasions the phosphorous content was found to be 56 and 107.
Another notable difference was that the snow cover was significantly less during the time of the 'Black Hole.' The snow acts as a layer of insulation, as well as a reflector of light. Plant life at the lake bottom could have been affected by this difference.
After two consecutive Winters, the 'Black Hole' disappeared as mysteriously as it arrived. It hasn't been seen since February of 2003. It would take another year for the mystery to be solved.
Now you must use your Geo-Senses to solve the mystery of the Black Hole!
Other Interesting Facts:
- The 'Black Hole' inspired an award winning independent film entitled The Hole Story.
- It also drew the attention of major news networks such as ABC.
- Multiple research firms did research on the cause of the 'Black Hole.'
- Over $10,000 was spent in pursuit of the answer.
- This is the first Earthcache in the Brainerd area.
To receive the smilie for this cache, email the Cache Owner the answers to the following questions:
1. In what stage of glaciation were these lakes formed?
2. In which direction did the glacier retreat?
3. List four of the lakes featured at the top of the geological marker.
4. What was the cause of the black hole? *
* Info for this question is hidden on the cache page, NOT at the cache site
You will know when you have found it based on the information and the nature of the 'hide'
Optional: Post a picture of yourself at the site.
[NOTE] The Cache Owner reserves the right to deny 'found it' logs if the answers to these questions are not supplied or correct.
If the answers are not supplied within a 24 hour time period, the log will be deleted.
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Additional Hints
(Decrypt)
Gur nafjre gb #4 vf whfg orybj gur rirag 'ubevmba'.