Bubbles in Harris Lake EarthCache
-
Difficulty:
-
-
Terrain:
-
Size: 
(not chosen)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
A kayak, canoe or small boat is needed to access the Earthcache site.
Coalbed methane gas is a form of natural gas extracted from coal beds. In recent years it has become an important source of energy in United States, particularly here in Alabama in the Black Warrior Basin where it accounts for about 48% of all natural gas produced in the state. In this area, the extraction of coalbed methane gas has resulted in the development of nearly 5,000 shallow methane gas wells.
Geologists use the term "basin" to describe a broad area where layered sedimentary rocks sag thousands of feet downward into a "bowl" shape, although there is often no evidence of this at the surface. The Black Warrior Basin is composed of Paleozoic rocks, some of which date back 580 million years. This region is also famous for its vast coal reserves, such as the Warrior Coal Field. Methane is a by-product of the geologic process that turns organic material into coal.
Coalbed methane has presented coal mining operations a serious safety risk, as the gas is stored in the solid matrix of the coal. Confined in a mine, the methane gas is highly flammable and explosive. The methane gas encountered in mines is normally wasted into the atmosphere. The methane gas is released into the mine when the coal seam is depressurized through fracturing of the coal seam and decreasing the water pressure by pumping water from the mine.
Natural seeps of methane gas occur in this area of the Black Warrior Basin. Here at this Earthcache, you should see bubbles coming to the surface of Harris Lake. Fissures in the bedrock under the lake allow the gas to move and be released into the water and then into the air. These seeps are also present on shore, but with the low pressure venting and the gas having no smell, the locations are difficult to spot. The seeping coalbed methane gas dissipates quickly in air, and poses no danger. Campers and fishermen have located some of these seeps next to the shore line and use them as a heating source for cooking, with the blue flame of a methane gas burning as is released through a rock fissure.
To log this Earthcache, visit the site at the posted coordinates, and answer the following questions. Email the answers to the CO, and post a photo of your visit if you wish.
Do you think the volume of gas bubbling up here at the Earthcache site is enough for a coalbed methane company to capture?
Do you detect any odor from the seeping gas?
The bubbles come to the surface of the lake in several places; is there a pattern to the locations of the seeping gas bubbles?
Additional Hints
(No hints available.)