Warning: My local creek bed in Boulder looked totally different after the spring floods

I hike past this spot every week, and last year the exposed rock was mostly smooth sandstone with a few pebbles. After the heavy rains in April, there's now a fresh layer of jagged, dark gray shale fragments covering everything. Is this a normal amount of change for one flood season, or did something unusual happen with the water flow?

3 comments

3 Comments

brookepark2mo ago

Lol isn't that just how creeks work though? Water moves stuff around. I've seen my local spot get totally rearranged after a big storm, it always looks different. It's probably just normal erosion, not some weird water flow thing.

noah9172mo ago

But @brookepark that's exactly why it's weird. Normal erosion moves stuff slowly, not all at once like someone flipped a switch. If the whole creek bed changed overnight with no big rain, that's not just water doing its thing. I've seen places where the flow pattern reversed for no clear reason, like the water found a whole new path. That points to something underground shifting, not surface erosion. There's a big difference between normal change and sudden weirdness.

wade7671mo ago

noah917 bringing up underground shifts is actually pretty smart. I've been reading about something called "knickpoint migration" where a change upstream can send a wave of erosion downstream all at once, not slowly over time. If a beaver dam or a big log jam gave way upstream from your spot, that could release a pulse of water carrying all the jagged shale from farther up the watershed. The smooth sandstone being covered by fresh, sharp fragments sounds exactly like that kind of event, not just rain on your local stretch.