Sinkholes

If you've driven up I-75 through northern Michigan, you may have seen signs for "Mystery Spot!"  That's a roadside tourist business which some say is pretty neat (I've never stopped there, but it's on my bucket list).  Even more mysterious, I suspect, are the sinkholes in Alpena and Presque Isle counties.

Sinkholes are depressions in the ground resulting from dissolution of carbonate rock by groundwater.  Geologists refer to this phenomenon as a karst process.  Over time groundwater can hollow out a cave in, say, limestone bedrock or salt beds.  Eventually, the cave's roof can collapse, creating a depression we call a sinkhole.  Some sinkholes are dry, while others are water-filled.  Sometimes an underground river can flow through the sinkhole on its way to... somewhere else.  In addition, sinkholes can develop suddenly.  This past week the news showed film of a young woman, strolling along a sidewalk in a city in China, who suddenly drops into a deep sinkhole (she was rescued with only minor injuries).

Northeastern Lower Michigan, especially Alpena County, boasts one of America's largest collection of sinkholes.  As Wikipedia notes, "In Lachine, Michigan [near Grace Episcopal Church in Long Rapids, where I preside at Sunday services twice monthly] there are five sinkholes that are found to be very deep and within 2 miles (3.2 km) from each other... In August 1998 a 16 year old Alpena boy survived a 200 feet (61 m)+ fall in an open sinkhole .75 miles (1.2 KM) from Leer road in Lachine, Michigan... A majority of sinkholes in Alpena are also found underwater.  Many divers explore these on a regular basis." (Sinkhole, at Wikipedia)

Less well known are a set of sinkholes in Presque Isle Township, a mile off East Grand Lake Rd.  Located on state-owned land, these sinkholes will soon be incorporated into a new park linking Besser Natural Area with Rockport, a no-longer-used harbor.  Presque Isle Township is actively involved in development of this facility which will offer hiking trails, equestrian trails and equestrian camping, off-road vehicle trails, bird-watching, and an activities building.  If all goes as planned, the boundaries of NOAA's Thunder Bay National Marine Sanctuary will be expanded along this part of the Huron shore to protect shipwrecks in the area.  If so, this new park will become a staging area for scuba divers diving on these shipwrecks.

At Sunday's meeting about township politics, the new park came up for discussion.  Patrick, our Township Supervisor, told us that some years ago the Michigan Department of Natural Resources wanted to determine if one of the water-filled Presque Isle sinkholes was connected underground to other bodies of water.  To this end they introduced a special dye into the water.  Such dyes include "chemical markers" which allow the dye and its source to be positively identified when it is found in another body of water.  Patrick said that several months later the Presque Isle dye was found in Detroit's salt mine!  Imagine that!... from Northeast Lower Michigan to Detroit, all underground!

For more information on the area's sinkholes, go to:
http://www.youtube.com/watch?v=2X0D1B1QGYA    •••