GLACIAL GROOVES
Glaciers are rivers of ice. Ice is a mineral (H2O).
Glacial ice is a rock (technically, a metamorphic rock). Despite being
solid, ice does flow under certain conditions at the Earth’s
surface. Occasionally, Earth experiences Ice Ages, during which extensive
ice sheets cover and move over significant portions of the Earth’s
surface. As ice moves over landmasses, it erodes underlying rocks and
picks up small to large pieces of debris. This debris accumulates at the
base of the ice sheet and scrapes bedrock as the glacier moves, resulting in
glacial scratches (glacial striations) (= thin scratch lines on rock) and
glacial grooves (= large channels incised in rock).
Glacial grooves on Columbus Limestone (lower Middle Devonian) from
Kelleys’ Island, western Lake Erie, USA (public display, Field Museum of
Natural History, Chicago, Illinois, USA).
Glacial striations (glacial scratches) & glacial polish (shiny
areas) on limestone from Lemont, Illinois, USA (FMNH G 675, Field Museum of
Natural History, Chicago, Illinois, USA).
Glacial striations (glacial scratches) on Columbus Limestone (Middle
Devonian). The glacial scratching occurred during the Wisconsinan
Glaciation (late Late Pleistocene). ~4.7 cm across.
Locality:
quarry ~2.4 miles east of Watkins, immediately northeast of intersection of
Watkins Road & State Road, eastern Mill Creek Township, southeastern Union
County, central Ohio, USA.
Collected 9 April 1967 by Lee St. John.
Glacial grooves in Columbus Limestone (lower Middle Devonian) at
Glacial Grooves State Park, northwestern Kelleys’ Island, western Lake
Erie, USA. These spectacular, world-class glacial grooves were carved out
during the Pleistocene (the last Ice Age).