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In some parts of the world, a 100-ton boulder composed of pink granite is an unremarkable thing, but that’s not the case in the Prairie State. So when scientists with the Illinois State Geological Survey in Champaign were contacted last year by Mike Waite of Jefferson County with photographs of such a beast, they made a point of going to see it when another job brought them to the area.
The boulder Waite showed them now rests in a creek bottom, about half a mile’s walk from the house where he and his wife, Sarah, live, on property that has been in her family since 1918. It measures approximately 22 feet x 10 feet x 11 feet, which makes it the biggest rock of its kind in the state, at least as far as anyone concerned knows. [Photo by David Grimley depicts ISGS geologist Dick Berg atop the Elephant Rock, with Mike and Sarah Waite alongside it. The segment of the rock above the dark band is the part that was visible above ground before the movement of the creek exposed the rest.]Its kind is “glacial erratic:” “Erratic” because it is unlike any rock that occurs near the Earth’s surface where it lies, and “glacial” because a glacier is the only force powerful enough to have put it there.
Sarah Waite’s family has enjoyed Illinois’ largest glacial erratic as a curiosity for as long as anyone can remember; her mother, who was born in 1926, recalled being taken to it as a child. They name it the “Elephant Rock” because up until recent years only a part of it protruded from the ground, and that part reminded them of an elephant lying on its side. Since the 1930s they have gathered at Elephant Rock for family photos, in a group that now includes up to 35 people.
The full size of the “Elephant Rock” became clear only when the meandering of the nearby creek scoured away the soil around it, allowing it to roll down into its present position.
Where did the Elephant Rock originate? Probably somewhere in northeastern Ontario, according to David Grimley, one of the geologists who went to look at it. That area is part of what’s known as the Canadian Shield, a vast region of igneous and metamorphic rock around Hudson Bay, an area where granite like that comprising the Elephant Rock may be found at the surface.
Imagine that. A 100-ton boulder riding as much as a thousand miles on top of or inside a vast sheet of ice, passing right by us on its way to the southern part of the state. The farthest south any glacier ever advanced in the Northern Hemisphere was only 50 miles beyond where the Elephant Rock landed, so it traveled just about as far as it possibly could have.
Grimley pointed out that geologists understand something about the timing of the Elephant Rock’s journey, too, since the last glaciers that could have moved it extended into southern Illinois some 150,000 years ago.
Unfortunately, the Elephant Rock is not situated where people can go see it for themselves, but Sarah Waite pointed out to me there is an accessible natural attraction nearby. It is the state’s largest flowering dogwood tree, certified by the Illinois Big Tree Registry, which grows in the Union Chapel Cemetery, about seven miles east of the town of Dix.
Closer to home, the University of Illinois Institute of Natural Resource Sustainability, of which the ISGS is a division, will host its annual expo, Naturally Illinois, on Friday and Saturday of this week. The expo will feature more than 50 science-based exhibits, activities and demonstrations for all ages. Further details available at http://www.inrs.illinois.edu/expo/.
