NOTE: In a sad coincidence, as I was writing this post, (a continuation of the last two posts—click here to go to the first in the series), a man in Florida was killed when a sinkhole opened up below his bedroom. Today’s post discusses the interpretive topics of the project I was working on in Southeast Alaska, including sinkholes.
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Princes of Wales Island in Southeast Alaska is karst country. Karst is a landform that develops when water dissolves the carbonate bedrock, resulting in unusual features such as caves, sinkholes, shafts, disappearing streams and caves.
The following illustrations are details from the first sign of my project at Beaver Falls Interpretive Trail.
In limestone caves, features such as spires, pinnacles, soda straws, stalactites and stalagmites take thousands of years to form.
Soda straws are delicate, hollow tubes that hang from the cave ceiling, growing longer with each drip.
Eventually soda straws build up layers of minerals and become stalactites. Below, stalagmites form.
This detail from one of the signs shows the influence wetlands have in the development of karst.
Muskeg, or peat bog wetlands above ground contain very wet, acidic soils that are a catalyst in cave development. As the water flows through the muskeg, it sometimes flows sideways across layers of hard clay until it finds a way down through the porous limestone.
The entire sign.
A detail illustration from a sign interpreting the karst formation of sinkholes.
Sinkholes are etched into the landscape as water trickles down from the surface. The second illustration in the sequence shows what happens when the “roof” wears thin and suddenly collapses.
The full sign.
Trees in Alaskan karst tend to grow larger because the soil is rich and the limestone helps anchor the the trees against fierce storm winds.
Many animals use caves to escape harsh weather, find safe places to nest, give birth or hibernate. Some creatures spend their entire lives in the darkest interiors of caves.
A detail illustration of the many species that use karst caves.
The signs were installed on an accessible boardwalk trail above the cave.
To find out more about Prince of Wales Island and Beaver Falls Karst Interpretive Trail, check out:
http://www.fs.usda.gov/recarea/tongass/recreation/outdoorlearning/recarea/?recid=78661&actid=119
http://www.cabinsinalaska.com/caves.html
http://www.flickr.com/photos/36970379@N06/sets/72157624357191916/detail/
The Pacific Northwest is not immune to sinkholes. In Shorelline, a city just north of Seattle, a giant sinkhole took out an intersection, just missing a nearby house. I designed some interpretive signs for the nearby park (written by Chuck Lennox). Check out the third sign in the series of project: Boeing Park
I’m not sure if there is karst around here on the Oregon Coast, but we have a little creek that goes underground in the dry months. I came across your illustrations on Jo Ann’s blog (http://woodandfield.wordpress.com/2013/05/27/karst-landforms-and-sinking-creeks/) and decided when the creek finally started flowing again, I’d take some pictures and provide a link to her post. Thanks for the most detailed illustrations. Beautifully painted, They really explain the whole karst, disappearing creek, and sink hole phenomenon.
http://solarbeez.com/2014/02/19/the-creek-runs-through-it/
Thanks, solarbeez. I’m not sure there is karst in Oregon, that would be an interesting subject to look up. Anyway, I hope your little stream doesn’t become a housing development!
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DENISE
I was thinking about the natural features of karst, caves, etc. with respect to hydraulic fracturing….
There is very strong resistance for several reasons to this “fracking” in many places where companies want to use this method for resource recovery. I know the fracking is done at 3000-5000 ft. down , but some water sources are that deep and methane is released to escape to the surface and thus passes thru natural under ground features. What is your opinion (?)….I am thinking it is short terms thinking for short term gains and who knows what the long term effects may be ?
Jackson
I’m no expert on fracking, but I do worry that the long-term consequences are unknown. There was a wonderful article in National Geographic (March 2013) on fracking in the Brakken shale of North Dakota. There was a map that showed the distribution of the wells—it was a good portion of the state— and it was literally covered with wells (they go vertically down for several miles then “dogleg” horizontally. The above ground effects are massive, too. Check it out if you get the chance.
So about those sinkholes….they have actually been a topic of watercooler wonderment at work–why are some perfectly straight down the sides while others are more like what one would expect from a cave-in?
Yes, I wondered that too when I saw the photo of the perfectly round sinkhole in Guatemala City, if that’s the one you’re talking about. I’m no expert, of course, but it looked to me like something other than a karst formation. I looked it up on the internet, and got various versions of the same thing: “ground water causes erosion underground in the shape of an arch, which when it collapses makes a round hole”. But, that doesn’t explain how the water is eroding in the shape of an arch! Thanks for nothing, Internet! To me, the really round ones look like something caused by flowing liquid, like maybe a lava tube. Lava tubes are hollow because the flowing lava cools and solidifies from the outside in. Maybe there was a solid “roof” over the tube that gradually weakened until it collapsed. But, please don’t take my word for it! I’m just an artist with a wild imagination, after all…not a scientist. Aren’t there any geologists out there that can answer this properly? Actually, now that I think about it, the Guatemala sinkhole looked rather like a giant core sample. Like maybe from a giant geologist. Hmmmmm. Makes you think, doesn’t it? 😉
Well, soda straws–you learn something new every day.
Yes, sad coincidence –that sinkhole opening up in Florida. I was surprised at how much coverage that story received–I heard it reported on the BBC too. But I suppose that in addition to the oddity of it, there was probably something about being in the safest place–our bed, at home–and the unknown danger beneath.
Thanks, Pat. Yes, it goes back to the fears of childhood, and that mysterious space under the bed. Chilling.
Such a great post… I learned a BUNCH about something I’ve always been intrigued by. The area I was born (Central FLA) was apparently once plagued by these natural phenomena (this was before Disney arrived, and dredged up all the natural swamp and wetlands).
Thanks, Fey Girl. It was kind of sad timing, given what just happened in Florida…but karst is a subject I’ve long been interested in, especially since that project in Alaska. It does make me glad I live on a non-karst hilltop, though.
What an informative post! We have karst soils in the Blue Ridge. Your illustrations helped me to understand how a creek that has traveled the same channel for hundreds of years can suddenly disappear, flow underground, and reappear miles away.
Thanks, Jo Ann. Karst is a tricky place to live, not only because of unpredictable things like sinkholes, but because the watersheds are partially hidden underground, so it is harder to track where water comes from and where it goes. It can make it difficult to protect water quality from contaminants. But the caves are beautiful! Very fragile, though. Glad you enjoyed the post!