Apologies (ish, not really) for the kind-of Game of Thrones reference, but it just works so well! Many of the iconic landscapes in Washington were formed by fire (e.g. volcanoes and other processes associated with molten rock), and then shaped by ice- in the form of glaciers!
Glaciers are essentially giant masses of ice that form in high altitude or high latitude regions where yearly snowfall in the winter exceeds snowmelt in the summer. As the snow collects year-round, additional layers of snow will compress the snow underneath into glacial ice. And soon (geologically speaking), the newly formed glacier will have enough mass to begin flowing downslope!
As the glacier flows downslope, the mass of ice does an incredible amount of work on the landscape. Those giant, deep valleys of the North Cascades? Carved by glaciers! Those high, pointy peaks in the Olympic Mountains? Glaciers! Most of the landscape in the Enchantments? You guessed it- glaicers!
But it’s not only the really big features that glaciers leave behind once the ice melts, there are many other smaller features that you can use to determine if a location was once occupied by a glacier.
A lot of the erosional work done by glaciers comes from rocks that become frozen at the base (bottom) of the ice. These rocks range in size from tiny sand particles all the way up to house-size boulders. The rocks are also angular and jagged in shape, and as the glacier moves these rocks scrape and grind away at the bedrock the glacier is flowing over. Imagine taking a piece of very coarse-grit sandpaper, and running it over a block of wood. What’s left behind? Lots of scratches in the direction that you moved the sandpaper!
The exact same thing happens with glaciers. Rocks frozen into the base of a glacier will scrape the bedrock underneath, leaving behind scratches- or striations- that we use today to identify locations where glaciers were, and what direction the glacier was flowing in!
This photo is an outcrop along the trail to Inter Glacier and Camp Schurman on the White River side of Mt. Rainier. The remnants of Inter Glacier proper are in the background, but the darker rock in the foreground is covered in glacial striations! You can also notice that the rock is pretty smooth and polished, aside from the striations. Larger rocks in the base of a glacier will leave behind the deeper scratches, while smaller ones will act as finer and finer grit “sandpaper” and polish the rock smooth.
So if you’re ever wondering or wanting more evidence that where you are hiking was once covered by a glacier, check out what you’re walking on! Striations and polish are pretty straightforward to identify, and always a fun find. 🙂