Brief-Form Post #39: Pits, Mounds, and Sinkholes in the Wells Memorial Forest at Monte Sano State Park!

Brief-Form Post #39

I am pleased to add the 38th of my GBH Brief-Form Posts (Less than five minutes to read!) to my website. I get wordy with my routine Posts. I don’t want my enthusiasm for thoroughness and detail to discourage readers. So, I will publish these brief Posts regularly.

Sinkholes, Pits, Mounds, Hummocks, and Hollows

Alabama State Park Northwest District Naturalist Amber Coger and I hiked the Wells Memorial Trail at Monte Sano State Park on December 4, 2024. We found multiple woodland delights: massive grapevines, active decay (and incredible mature puffball mushrooms), and a landscape of sinks, pits, mounds, hummocks, and hollows. The aggregate would have overwhelmed a single Great Blue Heron photo essay. Instead, I offer three distinct Brief-Form essays, this one focusing on sinkholes, pits, mounds, hummocks, and hollows.

I previously snapped the photos below at other locations to demonstrate the natural processes creating pit and mound…humoock and hollow… microtopography. A large living tree uproots, lifting a mass of roots and soil vertically as the trees slams to the ground. The pit or hollow is immediately evident. Imagine the root matrix decomposing and the rootball soil and organic matter settling adjacent to and aligned at 90-degrees to the toppled trunk.

I recorded this 56-second video of Amber exploring this very distinct pit on the uphill side of a long-ago fallen tree. The tree’s roots and trunk have long since decomposed.

This tree and the vast majority of the trees creating the distinctive hummock and hollow microtopography fell downhill.

This area is riddled with prominant pits and mounds.

Limestone Sinkholes

Unlike the tree fall microtopography, sinkholes are an artifact of parent material. The US Geologic Society defines a sinkhole as

A depression in the ground that has no natural external surface drainage. Basically, this means that when it rains, all of the water stays inside the sinkhole and typically drains into the subsurface.

Sinkholes are most common where water soluble limestone is the underlying parent material, which is the case along the lower Sinks Trail and throughout the Wells Memorial Forest. Over time, water dissolves the limestone, creating underground spaces that occasionally collapse leaving the conical depressions (dimples) on the forest floor. The entire Memorial Forest is a broad depression, where there is no surface exit. Individual sinkholes dimple the broader hollow.

Amber walked into this sinkhole (dimple) that is 25-feet across and 10 feet deep.

I recorded this 58-second video of Amber dropping into and ascending from the sinkhole.

Again, the entire Memorial Forest occupies an extensive bowl, providing rich limestone derived soil, abundant soil moisture year-round, and a micro-environment protected from the harsh effects of wind and sun exposure. Trees luxuriate, growing rapidly to large girth and exceptional heights.

Closing

I accept the challenge of distilling these Brief-Form Posts into a single distinct reflection, a task far more elusive than assembling a dozen pithy statements. I am educated, holding multiple degrees, yet I secured by far the greatest knowledge from an elective graduate course, geomorphology (taught by the late Dr. Ernie Muller), the study of the form of the earth. Because I can find no relevant wise quotation in the literature, I give you my own:

Learn the microgeography and you will understand the forest, appreciate its function, and interpret its mysteries, all at a higher level.