Integrative Natural History of Amnicon Falls State Park, Part 13: The Lower Falls, Taken Broadly | Wisconsin, USA
(Updated April 16, 2025)
This photo is the landscape-format equivalent of Part 12, so it too was taken from Horton Covered Bridge and is looking northwestward and downstream at the Amnicon River's middle branch.
In my previous post describing this superb Midcontinent Rift site, I discussed the geology of the bedrock visible here, the predominant tree species in this spot, and one strange kind of mammal often encountered in the park. So on this occasion I'll just make a couple of ancillary comments as the random idea generator of my brain presents them to me.
- The wonderful splashy turbulence of the Lower Falls is tinted a light yellowish tan for a reason, and it has nothing to do with anthropogenic (human-caused) pollution. There is no stinky paper mill nearby. In fact, streams in regions dominated by coniferous forests are often colored brown simply due to their high concentration of naturally occurring tannic acid.
Pines, spruces, and firs incorporate phenol compounds known as tannins in their tissues. These serve as a chemical defense system against fungal and bacterial invaders. When the trees' old foliage finally drops off, precipitation soaks through the duff (needle-leaf litter on the ground), leaches out the tannins, is turned a deep brown by them, and eventually ends up in North Country waterways. The water at the falls has a lighter tint because it's richly aerated. But you can get some sense of the normal darker color in the water this side of the falls.
- At the bridge we're 100 m / 109 yd downstream from the Douglas Fault and the contact with the Chengwatana Volcanic Group basalt. So the Orienta Sandstone on view here shows little if any effect of the tectonic disturbance caused by the motion and friction of the footwall and headwall when the fault was reactivated very late in the Mesoproterozoic.
In this locale the Orienta is very thin-bedded, and its strata are much closer to horizontal. But at the lefthand bend in the river, the expression of vertical jointing and sheet exfoliation is the dominant surface feature instead.
You'll find the other photos and descriptions of this series in my Integrative Natural History of Amnicon Falls State Park album.
Integrative Natural History of Amnicon Falls State Park, Part 13: The Lower Falls, Taken Broadly | Wisconsin, USA
(Updated April 16, 2025)
This photo is the landscape-format equivalent of Part 12, so it too was taken from Horton Covered Bridge and is looking northwestward and downstream at the Amnicon River's middle branch.
In my previous post describing this superb Midcontinent Rift site, I discussed the geology of the bedrock visible here, the predominant tree species in this spot, and one strange kind of mammal often encountered in the park. So on this occasion I'll just make a couple of ancillary comments as the random idea generator of my brain presents them to me.
- The wonderful splashy turbulence of the Lower Falls is tinted a light yellowish tan for a reason, and it has nothing to do with anthropogenic (human-caused) pollution. There is no stinky paper mill nearby. In fact, streams in regions dominated by coniferous forests are often colored brown simply due to their high concentration of naturally occurring tannic acid.
Pines, spruces, and firs incorporate phenol compounds known as tannins in their tissues. These serve as a chemical defense system against fungal and bacterial invaders. When the trees' old foliage finally drops off, precipitation soaks through the duff (needle-leaf litter on the ground), leaches out the tannins, is turned a deep brown by them, and eventually ends up in North Country waterways. The water at the falls has a lighter tint because it's richly aerated. But you can get some sense of the normal darker color in the water this side of the falls.
- At the bridge we're 100 m / 109 yd downstream from the Douglas Fault and the contact with the Chengwatana Volcanic Group basalt. So the Orienta Sandstone on view here shows little if any effect of the tectonic disturbance caused by the motion and friction of the footwall and headwall when the fault was reactivated very late in the Mesoproterozoic.
In this locale the Orienta is very thin-bedded, and its strata are much closer to horizontal. But at the lefthand bend in the river, the expression of vertical jointing and sheet exfoliation is the dominant surface feature instead.
You'll find the other photos and descriptions of this series in my Integrative Natural History of Amnicon Falls State Park album.