Blog#2

The Great Blue Hole is a sinkhole that was caused by the weathering of limestone dissolved by subsurface drainage.  The rock found in the cave of the Great Blue Hole is limestone karst.  It is believed that at the end of the Great Ice Age, as glaciers melted, sea levels rose, forcing more groundwater through the open spaces in the limestone karst.  As the rock dissolved, caverns developed underground.  The stalactites, stalagmites and columns were formed by calcite deposits from the chemical dissolution of the limestone.  

Illustration of how Caves/Caverns form

Illustration of how Sinkhole forms

 

The depth and isolation of the sea floor at the bottom of the Great Blue Hole has resulted in an interesting soil profile.  In 1997, divers took core samples from the bottom of the Great Blue Hole.  The 2-foot long core samples showed a long history of sedimentary layers. There is no oxygen near the bottom of the hole, and high levels of hydrogen sulfide prevent bottom dwellers from disturbing the sediment.  The samples showed layers of atmospheric fallout such as pollen, spores, as well as mercury, and arsenic.  The clay-rich sedimentary layers resulted in a gleization process, reducing the porosity of the soil, which caused the slow deposition and accumulation of organic material.  

Diver exploring the reef in the Great Blue Hole, approx. 60-80 feet underwater

 

Sources:

http://soundwaves.usgs.gov/2001/06/

http://www.news-world.us/pics/tag/coral-reef/

http://virtual.yosemite.cc.ca.us/chudelson/online/soils.htm

http://www.tulane.edu/~sanelson/geol111/groundwater.htm