Karst, caves and sinkholes


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.


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:




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