Once Upon an Ice Age

I remember the geology professor pausing in his lecture on the Ice Age and sighing wearily, like he had said the words a thousand times and was getting sick of it.

“I do not like the word RETREAT,” he said. “The glaciers did not RETREAT. They did not advance down in one direction, then turn around and march back in the other direction. They MELTED. The ice MELTED and the water DRAINED AWAY.”

Of course, this was well before the days of Global Climate Change, so perhaps our freshman class was not as savvy about things like melting ice. Still, the terminology makes a subtle but important difference. Water has shaped this planet in amazing ways, and it shouldn’t get short shrift. Especially when you consider the massive volume of water that was released when those towering Ice Age glaciers began to melt. In some cases—particularly in the Pacific Northwest—it made for some real drama: the Ice Age Floods.


The Ice Age Flood of Lake Bonneville

Lake Bonneville was an ancient Ice Age lake so big it covered almost half of Utah. (Today, the Great Salt Lake is a remnant of Lake Bonneville—a tiny puddle compared to its former self.) Lake Bonneville was a pluvial lake—in a landlocked basin fed by the heavy rains of the wet, cool climate of the Ice Age. On the northern side, Lake Bonnevile was walled in by a rocky ridge – a natural dam. In one place, today called Red Rock Pass, it was slowly eroding, the rocks giving way to the softer sands below.

Then, one day around 14,500 years ago…the dam broke.

Imagine…If you had been standing on the canyon rim at Swan Falls Idaho, above the Snake River, which today looks like this…


A watercolor I did that shows the present-day view from the canyon rim.



…you would have seen something like this…


There were people in the Snake River area back then – perhaps someone actually witnessed this…?



A 300-foot wall of water shooting down the canyon!

The force of the flow was so great, it ripped out chunks of the canyon walls and sent them hurtling downstream. Today, this is affectionately known as “melon gravel”. Here I am standing by one particularly large piece of melon gravel:


Several months ago, I was asked by my clients at Idaho Power to design a sign telling this story. Swan Falls is the site of one of their dams, and there is an interpretive kiosk that tells the story of the flood, as well as the history of the power plant and the Native Americans that once occupied the canyon in winter villages.

Here is the finalized design for the Flood Sign:

DDahnSwanFalls [Converted]



If you’re ever in the Boise area, take a drive out to Swan Falls and check it out. It’s well worth the hour drive, and if you like historic power plants, you can arrange for a tour of the very cool old plant, too.

Plus, the interpretive signs (installation due in 2014) are going to be pretty great.




Add your thoughts:

What do you think! Have you ever been to Swan Falls, or another site in the Snake River Canyon? Have you ever heard of the Ice Age Floods?


Learn More:


Read a short article and watch a cool slide-show

Read a longer, more in-depth article on Lake Bonneville and implications for climate change research

Visit the Ice Age Floods Institute

Check out one of my other posts about flowing water, including a section on the Missoula Floods