Geology Picture of the Week, September 7-13, 2003

Karst country in China -- landscape doesn't get any better than this.

I recommend this guy's photography (linked in header) for many areas of the world.

Why is this Karst?

I thought a Karst area involved vast areas where extensive underground caverns broke down and the resultant sinkholes drain into the cavernous area. There are extensive karst areas in East Tennessee and also extensive caves.

The formations pictures resemble sandstone arches in Utah and also here in East Tennessee resulting from surface river action.

Note that Smokin' Joe properly called this "late stage" karst development. What you describe is earlier stage. In late stage, much of the limestone has eroded away, leaving only the remnants of the former topography. I.e., late stage karst is more sinkhole than stone.

Precisely! As the caves expand in size, the roof collapses, leaving the pillars between the caves, which are, in turn weathered. The cave system here most likely formed along sets of intersecting fractures, (imagine them as a large grid). What you see are the remains of the rock from the center of the boxes in the grid.

If that gives you trouble, doodle it out. Take a piece of scratch paper and draw sets of nearly parallel intersecting lines. These are the fractures. Expand the lines--as water moving through fractures can expand the cracks into caverns.

Keep in mind that this is happening in three dimensions, and holes start developing in the roof (sinkholes)as it thins by being eroded from below.

As erosion continues, sections of the cave roof collapse, leaving natural bridges, canyons, and large blocks of relatively uneroded limestone.

As erosion continues further, all that is left are the distinctive mound-like features you see in the photo. Eventually, these too will be eroded away.

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