Leonard Springs and the polar vortex

Walking along Ridgetop Road toward the Leonard Springs Nature Park trailhead, I wasn't sure what to expect in a winter season more suited to Northern Minnesota than Southern Indiana. It was my first trek there in winter, and I hoped the waterfalls below would be a mass of gleaming ice sculptures reflecting a brilliant February sun. But I knew better than to expect the expected from karst topography.

A few steps down the stairway, whose precipitous descent leads just beyond the Shirley Springs Shelter Cave, part of the answer revealed itself, bringing to mind a two-century-old John James Audubon quote. “The rumbling sound of the waters as they tumble over the rock-paved rapids is at all times soothing to the ear.”

Audubon was writing about the Falls of the Ohio a hundred miles to the south. But his observation befit the polar scene this Friday afternoon at Shirley Springs. The water was indeed running, despite the sub-zero temperatures that preceded the moment just hours and weeks before. In places, the flow had frozen over limestone ledges into glistening, bulging, icicle formations, mere inches from still-running, splashing water. Such is the marvel that is karst topography.
 
Named after the other natural spring that drains to the wetland below, the 95.5-acre Leonard Springs preserve is owned and managed by the City of Bloomington Parks and Recreation Department.

Southeast Monroe is karst topograhy, characterized by landforms that are underlain by soluble rock – limestone at Leonard Springs – and contain natural features like caves, sinkholes, and underground rivers and streams, to mention but a few. The water that emerges from the park's two large alcoves has flowed miles underground.

Leonard and Shirley Springs release enough outflow to provide water for a community, which they did a century ago. The city purchased the property between 1914 and 1917 and dammed it. But like Wapehani and other reservoir projects built on karst, Leonard Springs leaked. In 1943, it was drained and abandoned in favor of the larger, more stable Lakes Griffy and Lemon to the north and east.

In 1998, after a half century of natural selection, Leonard Springs changed hands. The Utilities Service Board sold it to the city parks board, which established the nature preserve the next year.

On Friday afternoon, Shirley Springs Cave, on the north side of Ridgetop Road, was “breathing” – releasing warm, moist air from the entrance that turned to steam in the low-20s temperatures.

Across the road, the staircase steps that begin the 1.1-mile loop trail were ice-free and easy going. Bare trees offered unobstructed views of the hillside, anchored with a mature hardwood forest, that descends 180 feet to the old reservoir bottom.

From the staircase's end, a set of footprints led to the slim, snow-covered bridge over the stream that still ran a few yards downhill from the falls. A City of Bloomington brochure says Shirley Springs doesn't dry up, even in droughts, and, obviously, not during an Arctic winter, either.

The footprints continued on toward the bottomland, where the trail Ts, with a spur to the dam and a loop around to the east end of Ridgetop Road. In addition to the karst features, depending on the time of year, the trail features a diverse mix of plant and animal life, fossils, chert and historic stone structures.

Due to cold and other obligations, I turned back at the bridge, with the knowledge that not even a polar vortex can overwhelm karst, not to mention more than a few photographs for my effort.

I left with a curiosity about what's happened downstream. 

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