As I understand it, its a lot more interesting an violent than that even. Based on what I've read about the geologic history of Rock Creek, the main conduit for transforming the lower falls was the possible collapse of an underground lava tube roughly beneath the channel of the creek where the lower falls used to stand. There are several old pictures of a waterfall on Rock Creek which I presume to be the lower falls pre-alteration (below) and if this is indeed the same waterfall, the collapse of the lava tube allowed the creek to bite into the bedrock very heavily and basically pushed the brink of the falls upstream a good 200-300 feet in the last 60-70 years.chameleon wrote:Bryan, as I was researching Rock Creek, I came across something you might find interesting. Remember that old book I pointed you toward a while back the Mazama one from 1915? Anyway, in it, he describes both Rock Creek falls, and the description of the lower one differs dramatically from what we have today...
"On Rock Creek less than a mile above Stevenson, the stream passes over a ledge of sedimentary rock, and drops in a broad sheet for almost a hundred feet. A short distance above is a similar fall of lesser height. These falls differ from the others in spreading their flow and pouring over the brink in a broad sheet, and not in a concentrated mass, as do the streams on the Oregon side."
It seems that due to the crumbly nature of the lower falls, its shape has changed a lot since then. Not only that, but its not nearly as tall (albeit, the author of that article is prone to exageration about falls heights in the first place...but still). It seems that it has been doing a fair job of carving its way down and creating a muddy notch rather than a broad shelf. Anyway, thought you'd find that interesting.
-Zach
Upper Rock Creek Falls in 1936, not much changed since then:
Lower Rock Creek Falls in1936, HUGE difference:
Now I'm not sure about the whole 'lava tube collapsing' thing. It looks like another possibility is the lower falls just punched a deep pool in the soft bedrock deep enough that a crack opened which allowed a pool retained behind a small natural dam to break and scour out the less steep parts of the cascades, and that the actual brink of the falls hasn't moved in the 74 years since those pictures were taken. Either way, one of the best places to witness the power of water.