Not sure if folks who visit Mt Adams ever notice, but it has a lot of springs that pop out of the mountain side, and some of them have quite a huge flow. The short geology lesson is that although it is a volcano, it is not the exact same rock type as most of our NW volcanoes. It is a kind of rock that ironically degrades in the presence of volcanic gases, to the point where the rock cannot support it's own weight. Mt Adams frequently (on a geologic scale) has landslides. Those landslides cover existing surface streams, which now are underground streams, but must find an outlet somewhere - voila, a spring!
Two hundred years ago, one of them covered present day Trout Lake and USGS reports speculate on a massive one that could dam the Columbia. There has also been preliminary discussion of an early warning system for Trout Lake so folks could flee for high ground. But the technology does not yet exist and so far there is no funding.
Take a look at all that degraded yellow rock in this photo in the Salt Creek region on the SW side of Mt Adams, the part of the mountain currently most prone to slides. Around the trail, the rock is the same color and the trees fairly small. Some tree core ring counts would presumably tell you when the last slide was in this area.
- Degraded rock above Salt Creek
You can buy Darryl Lloyd's book, Ever Wild, if you want a much more detailed description of the process of degraded rock and how Mt Adams is, literally, rotten to the core.
One spring that is widely reported and seen is midway up the PCT from Road 23 to Horseshoe Meadow, it forms the primary headwater of the White Salmon River. But the best one to go look at now if you are so inclined is farther south, in the vicinity of Salt Creek. Walking NW on the Round the Mountain Trail from the Shorthorn Trail junction, while crossing a number of tributaries of Salt Creek, at one point you will hear water where none is crossing the trail. This is what it looks like from above.
- Looking down from RTM trail
If you continue slightly further and work your way down, this is the outlet.
- Springing forth
The water lets loose on a flat rock and quickly spreads out. The outlet in the previous photo is actually under the branches in the lower left of this photo.
- Spreading spring
Here is a different view just 20 or 30 feet downstream
- a new river
That there is no obvious water erosion suggests to me that this spring probably pushed out creating this spring fairly recently, whatever that works to be. It's barely over three miles hike to see this, but it tends to dry up quite quickly in the summer, so don't wait long if you want to go. I'm guessing some minor amount of flow stays underground after that.
