Glacial grooves on Kelleys Island.
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). The world-class glacial grooves seen here were incised on Devonian fossiliferous limestone during the Pleistocene (= last Ice Age). From public signage: GLACIAL GROOVES STATE MEMORIAL Welcome to the Glacial Grooves State Memorial. This memorial, consisting of three and one-half acres on Kelleys Island, has been administered by the Ohio Historical Society since 1932. Impressive in size and shape, these glacial grooves are of great geologic significance as well. Approximately 25,000 years ago, when the climate was much cooler and wetter, a great continental glacier flowed from Canada into northern Ohio. After the climate warmed and the ice melted (about 10,000 years ago), this island retained a spectacular reminder of the glacier’s presence here -- these huge glacial grooves, which had been carved in the limestone bedrock by the action of the advancing glacier. Due to their size and ease of accessibility, these are the most famous glacial grooves in the world. Since this formation was discovered over a century ago, it has been an object of fascination to students, vacationers, and scientists alike. Geologists have studied these grooves for many years in an effort to determine exactly how they were carved by the glacier. Several theories have been proposed, but there is still no entirely satisfactory explanation. THE OHIO HISTORICAL SOCIETY 1977 OTHER GROOVES Have you noticed any other glacial grooves on Kelleys Island? There are still more grooves, mostly smaller than those featured here, to be found throughout the island area as well as on the mainland. Several examples of grooves, striations, and planed surfaces may be found in the Kelleys Island State Park along the north shore of the island just north of the Glacial Grooves State Memorial. Some very spectacular grooves which were destroyed during quarrying operations on the island were called the “Great Grooves”. These grooves extended for at least 2,000 feet with maximum measurements estimated at 15 feet in depth and 30 feet in width. ISLAND HISTORY The human history of Kelleys Island is estimated to extend back to the early 1600s. There is evidence that during that time the island was the home of at least two Indian villages, probably of the Erie (or Cat) nation, which was annihilated by the Iroquois in 1665. The petroglyphs of Inscription Rock, on the south shore of the island, were probably carved over a period of years by the Eries and may describe certain important events in their history. A man named Cunningham is believed to have been the first white man to inhabit the island, living here from about 1800 until about 1812. The island became the property of the Connecticut Land Company in about 1817 and was divided into 13 lots which were given to stockholders in the Company. In 1833 the Kelley brothers, Datus and Irad, immigrants to the Cleveland area from Connecticut, began to buy the parcels of land and soon owned the entire island. The Kelleys and their families began developing the island and its industries - wine-making, quarrying, logging, fruit-growing, and fishing - as well as encouraging the cultural enrichment of the inhabitants. Eventually the island, previously known as Cunningham Island, or island No. 6, became known as Kelleys Island. BEDROCK JOINTS The straight cracks running across the grooves are called joints. Joints usually form in sedimentary rocks, such as this limestone, as a result of the application or release of pressure on the bedrock. It is not known exactly how these joints were formed, but we can be fairly certain that some pressure change occurring before the advance of the glacier responsible for the grooves was a major factor in the formation of the joints. FOSSILS The fossils found in the bedrock of Kelleys Island are the remains of plants and animals which lived in Ohio many thousands of years ago when the area was covered by a shallow saltwater ocean. When these marine organisms died, they settled to the bottom where they became embedded in soft sediments. Later, as these sediments hardened into limestone bedrock, the remains of the organisms were preserved in place. Fossils of many kinds are very abundant in the limestone of Kelleys Island, and can be seen almost everywhere if you look very closely. Fossils are very useful to scientists in the study of early life forms, climate, environment, evolution, and the relative ages of different rock layers. THE QUARRY [= adjacent to this site] This quarry is one of several now-abandoned quarries to be found on Kelleys Island. At one time quarrying was a major industry on the island and the fine quality limestone found here was highly valued for its many uses. It was cut to shape for buildings, removed in large blocks for the construction of piers and breakwaters, burned to make lime, and crushed for use as flux in the production of steel. Kilns and crushers were built on the island in the early 1900s and the industry reached its peak in 1918. By this time most of the quarries were owned by the Kelleys Island Lime and Transport Company. By 1941, however, most of the quarries had closed due to the opening of quarries in Michigan which could supply limestone less expensively. One unfortunate aspect of the old quarrying industry was the destruction of many very spectacular grooves, some of which were more impressive than the ones exposed here today. The long vertical marks on the quarry walls were made by the drills used in quarrying operations. Before the use of machine drills and explosives, the holes were hand-drilled and pieces of green wood were packed into the holes. Water was then poured into the holes and the wood absorbed the water and expanded. The resulting pressure caused large sections of the rock to be broken loose from the quarry wall. THE TRIBUTARY Notice the small branch of the grooves extending away from the main grooves. Although no one knows for certain just how this feature was formed, it is sometimes cited as an argument in favor of the theory that the grooves were formed as glacial ice reshaped an earlier stream channel. If this were the case, this branch would represent a tributary stream which once flowed into the main stream, represented by the main grooves. The glacial ice, which is quite plastic at its base, would have molded itself to the existing stream channel. While confining most of its grinding and rasping to the channels of this former stream and its tributaries, it widened, smoothed, and deepened the channel, thus giving it its present shape and form. According to one theory, the tremendous grinding force resulting from the convergence of ice and a large concentration of debris in the confined space of the stream channel produced the extensive grooving seen here. GROOVE DETAILS The grooves, which for the most part are straight, are marked in many places with some very interesting details. The most noticeable in this spot is the tortuous winding of some of the smaller grooves and scratches, possibly due to pre-glacial or sub-glacial stream flow. This features was also noticed in some of the photographs of the “Great Grooves”, and others that have now been destroyed. There are sections where the rock seems to be undercut, and places where the formations indicate that the ice flowed around melon-shaped knobs, possibly due to some obstruction such as broken joints in the bedrock. In many places you may notice small grooves superimposed on larger grooves. It is common to see very fine scratches or striations on the limestone, probably caused by the scraping of sand parrticles in the glacier’s base. When the grooves were uncovered for the first time, after thousands of years under several feet of soil and debris, a high polish was noticed on some of the rocks. This polish was most likely procued by the scraping of clay. Soon after the rock was exposed the polish disappeared due to weathering. Weathering also caused the pitted effect noticed on some parts of the grooves. It is believed that these pitted areas were exposed to the weather once before, many years ago, and were later covered again until the most recent exposure was made. All these details are helpful to scientists in determining how the ice sculpted the grooves. Many clues are provided here, but the challenge lies in their correct interpretation. Stratigraphy: Columbus Limestone, Eifelian Stage, lower Middle Devonian Locality: Glacial Grooves State Park, northwestern Kelleys Island, western Lake Erie, Ohio, USA