Gibbs Falls on Gibbs Brook has made a very unusual movement in the very recent geological past.
All waterfalls are on the move, eroding their way upstream. But recently, the base of Gibbs Falls has moved nearly three feet sideways.
I first noticed this some time in the early to mid 1990s. For all I know, it may have happened just the day before I first saw Gibbs Falls, or it may have happened decades earlier. I can only be certain that something happened very recently, in geological terms.
Gibbs Falls is a pretty little waterfall, perhaps thirty feet tall, on Gibbs Brook in Crawford Notch in the White Mountain National Forest in New Hampshire. It is located about 3/4 of a mile up Crawford Path. There is a sign indicating a little spur trail off Crawford Path to a place where you can see Gibbs Falls.
Take a close look at the photo at the top of this page. Click on it to view the full-size version, or right-click and download the full-size version so you can view it in your favorite image viewer and zoom in on the details.
The falls may be divided into seven sections, based on the changes in direction and flow as the water tumbles from one ledge to another. These segments are labeled in the photo below.
In segment 1, the water falls at a steep angle until it hits a ledge. In segment 2, the water falls from this first ledge at an even steeper angle. In segment 3, the water flows horizontally across a ledge, and in this pool there is a large boulder. In segment 4, the water falls nearly vertically from the lip of the segment 3 ledge. In segment 5, the water falls at a steep angle across an angled protrusion in the rock face. In segment 6, the water falls vertically off the edge of the angled protrusion in segment 5. In segment 7, the water flows and spreads at about a 45 degree angle across the angled base of the rock face and enters the pool below the falls.
Notice to the left of segment 7, the rock face is polished very smooth, as if the water flowed there once, and for a very long time.
It's hard to see in these photographs (and maybe next summer I'll take a movie that will show these details better), but the rock behind the water in segment 7 is rough and jagged, as if the water has not been flowing there for very long. Also hard to see, there is a suggestion of polishing of the rock face to the left of the water in segments five and six as well.
Clearly, something has changed the waterfall in the recent past so that it now flows to the right of where it used to flow.
My best guess is that the change was caused by the boulder in the pool in segment 3. The boulder fell into the pool and impeded the flow of water across that ledge. It's a little hard to see in the photo above, but in the full-size version, you can see that the water upstream of the boulder stands quite a bit higher than that on the downstream side of that ledge in segment 3. In real life, you can plainly see that the water upstream of the boulder is roiling and splashing violently, but downstream of the boulder, it has lost its forward momentum.
I'm guessing that before that boulder fell into the pool, the water used to rush through that pool with the flow energy it had when it completed the fall in segment 2. Then, it had considerable forward momentum as it cleared the lip of the ledge in segment 3, which carried it farther out to the left as it began the plunge of segment 4. This change in angle would have continued down the remainder of the waterfall, so that the water would end up much farther to the left near the bottom, and would have flowed where we now see the polished rock in the cliff face.
What will become of Gibbs Falls in the future?
If the flow continues as it is now, the rock behind where the water now flows will be polished smooth. I don't know how long this will take, but the rock does not appear to be any smoother now than it was 25 years ago.
It is possible that a large flood will dislodge that boulder from the pool and restore the water to its original path. That would be very interesting to see, but I'm not betting on it. In the past 25 years, that boulder hasn't budged. Still, boulders do indeed move, and I have seen boulders dislodged from places where I thought they would stay for a thousand years.
I'll keep watching until I get too old to make the hike up Crawford Path.
By the way, Gibbs Falls is the waterfall I use as a vertical margin on the left-hand side of all pages of this Web site. That picture was cut from the photo at the top of this page.