Montlake - Lake on the Mountain

Located in Hamilton County, Tennessee, near Chattanooga, this is one of the most interesting natural lakes, of which Tennessee has few.

Montlake, Hamilton County, Tennessee 2
Geology of Montlake, Hamilton County, Tennessee [Map]
Montlake is a small lake near the rim of the Cumberland Plateau in Hamilton County, Tennessee. It sits close to the escarpment and has several striking features including sheer sandstone cliffs flanking most of the perimeter of the lake, as well as distinct sandstone joints zig-zagging southeast of the lake. The sinkhole itself trends south by southeast with another drainage heading southwest before turning 90 degrees and going northwest parallel to the cliff face. The lake is just over 3 acres at base height. Its depth is rumored to exceed 100' at its deepest location, but I cannot independently confirm this.

Initial investigation of this feature by myself, and early Tennessee geologists suggest that Montlake is a sinkhole. It's round shape and closed elevation contours certainly makes it appear so, but that it sits on the Cumberland Plateau, on top of hundreds of feet of sandstone makes that less likely, though not impossible. Later investigation points at this feature being caused by the slump of sandstone calving off the Plateau. That is supported 1) by its proximity to the edge of the Plateau and 2) by some canyon-like features running from the lake parallel to the cliffs of the Plateau.

I am not sure that either explanation alone sufficiently explains this feature. In my novice opinion it seems that it's both slump and karst. Which happened first is hard to tell, but slump doesn't explain the morphology, and fails to explain the nearby karst springs below. Karst fails to explain how the feature can exist through so many hundreds of feet of sandstone.

I welcome a more thorough explanation by someone who has investigated it first hand. It seems though that the experts on this are all long dead. This feature is on private property, please respect the landowner and obtain permission before visiting.

Measure Value Unit
Major Axis 522.76 Feet
Major Axis 162.48 Degrees
Minor Axis 319.08 Feet
Minor Axis 72.48 Degrees
Axis Ratio 0.61  
Pool Area 3.07 Acres
Pool Perimeter 1,394.99 Feet
Pool Elevation 1,576.81 FASL
Max Pool Elevation 1,607.79 FASL
Watershed 175.24 Acres
Pool Centroid 35.240800,-85.226331 WGS84
Pour Point 35.239839,-85.223737 WGS84

Laurence, Robert A. "Sinkholes of the Cumberland Plateau." The Journal of Geology 1937 45:2, 214-215. Web.
Stockdale, Paris B. "Montlake: An Amazing Sinkhole." The Journal of Geology 44.4 (1936): 515-22. Web.
Wilson Robert L., 1984: Slump features at Montlake in southeastern Tennessee; previously misinterpreted as a sinkhole. Abstracts with Programs - Geological Society of America 16(3): 206

Montlake, Hamilton County, Tennessee 1 Montlake, Hamilton County, Tennessee 3 Montlake, Hamilton County, Tennessee 4 Montlake, Hamilton County, Tennessee 5 Sandstone joint, Montlake, Hamilton County, Tennessee 1 Sandstone joint, Montlake, Hamilton County, Tennessee 3


Don't Drink Cave Water

It's becoming an almost daily routine that I feel obligated to share with people that they shouldn't drink cave water. This is me being lazy, so that I can simply point people to this essay in the future.

What do I mean by cave water?

Why shouldn't I drink water from a cave?

Recharge to karst aquifers bypasses the filtering capability of soil through macropores and swallow holes.

Water can be filtered through soils. However in many parts of karst regions there is little to no soil is present between the surface, and subsurface stream.

The Sinks of Little Brush 3

Groundwater flows through conduits so that there is little opportunity for filtration or sorption of contaminants onto aquifer material.

When water is able to flow through the grains of bedrock, the bedrock is able to filter and remove contaminants. In karst, the grains of the bedrock are dissolved and larger and larger conduits are created. Conduits, like caves, provide little, if any filtration of contaminants.

Evan Hart, Capshaw Cave, Putnam County, Tennessee 2

The movement of pollutants cannot be directly observed as in a surface-flowing stream.

In the system pictured below, there's a gap of several miles between where the water goes underground and returns to the surface.
C1 swallet detail, Spring Creek, Overton County, Tennessee 2

Flow paths may take routes that are not apparent from the topography or slope of the land.

These are huge issues. If I were to show you the overlay of a cave map on a surface map, would you be able to tell me where the subterranean drainage boundaries are? As in, if this gas station's tank started leaking, would gas enter this cave?

Currently, our toolkit for delineating a subterranean drainage basin is very limited. And it turns out their boundaries don't behave like surficial watersheds. Their boundaries are often gray, fading into and out of one another. Their boundaries are affected by stage, or the height of the water in the system, which is often not able to be observed directly. In the map below, the flow lines of subterranean water are simply to show you their source, and where they surface at. They are not accurate.

Delineation of a Major Karst Basin with Multiple Input Points, Roaring River, Tennessee - Map

Flow velocities in karst aquifers are fast compared to velocities in granular aquifers, allowing little time to warn downstream users following a reported spill.

This also means that if you got cave water tested yesterday and it was clean, it doesn't necessarily mean that it is today. Rapid contaminant transport is a major issue in karst regions.

Toilet Bowl Entrance to Trog Cave (system), Cookeville, TN

Flow is in converging conduits; therefore pollutants are not diluted through dispersal.

More accurately, I mean water from a karst spring, or cave. If you don't know what karst means, look here.