A Geological Tour by Alpaca Rob

I thought it was time you all heard from the Rock Hound himself, as I have made mention of his excitement about the geology of southern China. So, without further ado, here he is...known as the mild mannered hydrogeologist superhero to his blog fans...introducing Alpaca Rob.

Thank you Science Mom. I just want to say it is an honor and privilege to blog to the larger audience of the Science Mom.

First off, the Guangxi province has a complex geology. It has had some below surface (intrusive) volcanic activity along with a changing shoreline which produced the large areal extent of limestone (lots limestone all over the place). The intrusive igneous area is predominantly in the eastern portion of the province in the form of the world famous Cenxi red granite. The central and western portions of the province were, at one time, a large reef/ off-shore region that then became limestone. This limestone was pervasive and thick. But, being in a sub-tropical extremely humid environment, this limestone has weathered to formed what is called by us geo-types Karst topography.

What is Karst you ask?

Karst, is a complex landscape sculpted by water. It is a distinctive topography (land-surface) in which the landscape is largely shaped by the dissolving action of water on carbonate bedrock (in this case limestone but it can also be formed in dolomite or marble too).

This geological process, occurring over many years, results in unusual surface and subsurface features ranging from sinkholes, vertical shafts, disappearing streams, and springs, to complex underground drainage systems and caves.

How Karst is Formed
The process of karst formation involves what is referred to as "the carbon dioxide cascade." As rain falls through the atmosphere, it picks up CO2 which dissolves in the droplets. Once the rain hits the ground, it percolates through the soil and picks up more CO2 to form a weak solution of carbonic acid: H2O+CO2=H2CO3. The infiltrating water naturally exploits any cracks or crevices in the rock. Over long periods, with a continuous supply of CO2 - enriched water, carbonate bedrock begins to dissolve. Openings in the bedrock increase in size and an underground drainage system begins to develop, allowing more water to pass, further accelerating the formation of karst. Eventually this leads to the development of subsurface caves then sinkholes, and at the extreme end you get limestone towers ( as seen in Guangxi and the digipic below). The other picture is of Reed Flute cave which is in Guilin, which is one of the places that I would like us to go while picking up Esther.


So, there you have it! Geology 101 chapters 10 and 15 with a little of geochem 102 thrown in to boot. This is Alpaca Rob blogging, have a great day and watch out for the Karst. For more adventures in hydrogeology and nice digipics visit "Tales of AlpacaRob" at http://www.alpacarob.blogspot.com