Our Very Cool Local Islands

Field Notices

Luther College Chips
March 12, 2009

With the temperature pushing its way up into the balmy 40s, now is the time of year you can visit the islands in Decorah without bringing along a change of clothes.


That’s because the islands within walking distance of Luther are cool year-round.  Cooler yet, the creatures that live on these islands are almost frozen in time.


To appreciate my enthusiasm about this phenomenon, I have to tell you that the “Jurassic Park” of my childhood was the 1960 remake of a Sir Arthur Conan Doyle book, “The Lost World.”  That fine movie begins with Claude Rains assuring a meeting of London academics that "There exist today many forms of creatures long believed to be extinct."


Sure enough, before you know it Rains is lost with later-to-be-Bond-girl-in-skin-tight-slacks Jill St. Johns on a South American plateau still populated with dinosaurs.  When these oversized lizards aren’t fighting each other, they are terrifying their human visitors.  At the age of eight, I would have sworn to you that no way could movies get any better than that.  Had DVDs existed, I would have owned a copy.


Northeast Iowa’s lost islands aren’t populated by Jurassic monsters, but they are home to a miniature equivalent: Pleistocene snails.  Until the 1950s paleontologists used the remains of these “extinct” creatures to date Ice Age soils.  Then, around the time I was born, a researcher discovered a living colony of these snails.  Today, 37 different island colonies of Iowa Pleistocene snails have been discovered.  The Ice Age is alive and, well, slithering, in the Age of Obama.


And it’s all because of islands: not islands of land surrounded by water, but islands of cool, surrounded by a climate that every year gets very hot and these days is getting even hotter.


These little pockets of cool are mainly the product of regional geology.  The bedrock in this part of the Midwest is heavily cracked limestone.  Cold air, being heavier than warmer air, settles down through surface cracks and sinkholes, further cooling as it hits underground water that has often frozen during winter months. 


When it can settle downward no further, this refrigerated air flows out horizontally to the nearest rock face.  Brittle limestone often litters the base of rock bluffs in huge heaps of chipped stone.  The air cools these stone piles, creating algific (cool) talus (stone debris).  When an algific talus slope is further protected by facing north the area soon grows over with a loose mat of moss that further traps the cold to complete the island effect.


On such north-facing slopes of algific talus Iowa Pleistocene snails find their few remaining homes.  12,000 years ago, when mastodons roamed the region and glaciers stretched south into what is now Iowa, Pleistocene snails could have been found most anywhere.  With the warming of the climate, only these little islands of coolness provide the kind of environment where these nearly-but-not-quite extinct mollusks can survive.


To protect these endangered populations, as well as some equally rare and endangered associated populations of plants, the Driftless Area National Wildlife Refuge was created in 1989.  Though the Refuge extends from Northeast Iowa to Southwest Wisconsin to Northwest Illinois, its protection only extends to 300 tiny islands of rock scattered in a tattered archipelago across the region.


Lucky for you, a handful of those algific talus areas are within walking distance.  A scattering of them stretch along the Oneota Trail as it approaches the campground across the river from the college.  Look for areas where the 40-something-degree air has melted the snow at the base of rock faces in winter.  In spring, the green mosses and lichens on algific talus stand out from the still-brown foliage around them.  In mid-summer you can feel the cool air from these talus heaps flowing out over your sandals as you walk or bike past. 


Just west of campus the college owns piece of a north-facing bluff visible from the cafeteria.  There too, piles of rock in a little ravine between the main rock face and a lower row of outcroppings are matted with moss and stay cool through the summer.


If you decide to check out any of these islands, just remember why the National Wildlife Refuge was created.  The colonies are fragile.  You should not stomp across them (or even step on them), pull up the mosses, or transport away any portion of the remnant Ice Age landscape you find there.  Eye them respectfully, and from a safe distance.


So do something wildly exotic.  Go island-touring in Decorah.  But like Claude Rains on his plateau of dinosaurs: keep your distance from the natives!