One of the wonders of Denali National Park in Alaska it this beautiful body of water, seen here with mount Denali (6,168m) in the background. The landscape here is a combination of permafrost and tundra, deciduous Taiga forests and tall glaciated granitic mountains. The range of peaks is rising due to the subduction collision between the Pacific and North American plates that is responsible for the huge spine of the Americas, running south all the way from Alaska to Tierra Del Fuego in faraway Argentina and Chile.
The park contains fragments of several of the micro terranes that have accreted on north America's west coast over the last hundred million years or so. Many have been metamorphosed, melted into granites and extensively folded and faulted by the immenso tremendous forces of continental collision. In fact this process provides a slow motion rough and ready answer to the old quandary of what happens when an irresitable force meets an immovable object.
Most of the terranes were oceanic sediments that were too buoyant to subduct, and their rocks were originally deposited in a variety of eras. The oldest is the Yukon-Tanana (1 billoin-400 million years old), now extensively transformed by its geological journey into medium grade metamorphic rocks. Next in line is the Farewell, a fossil rich sedimentary slice from the early half of complex life's evolution, dating from the Cambrian to the end Permian. The youngest terranes date from the Mesozoic era and consist of mixed sedimentary and igneous rocks, including pillow basalts first erupted under a sea full of ammonites and swimming reptiles. there is also an ophiolite sequence, where a chunk of oceanic crust has been pushed onto the continent , giving us a lovely insight into the marine crust/ shallow mantle interface. The youngest rocks comrpise something known as a flysh sequence, built up in the marine basin below the mountains where the plate was flexing down under the force of the grating subducting plates around a hundred million years back. The mountains are still growing and the many earthquakes in the area testify to the powerful forces stirring below.
The recent ice ages sculpted all these rocks into the landscape we see today. Wonder lake itself is a glacial landform called a kettle, formed during the rapid retreat of the sheets when large chunks of ice melt more slowly than the rest because they are shielded by a protective layer of till (glacier shlep, rock dirt and flour). The overlying debris then settled and slumped forming the depression that has since been filled by rainwater and snow melt, though some of it was also directly carved out by glaciers. It is 6.5km long and up to 85 metres deep.
Image credit: Rodney Lough Jr/ Nature's Best Photography
http://www.nps.gov/dena/planyourvisit/campground-wonder.htm
