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).