The Quaternary Period began 2.6 million years ago and continues to this day. The Pleistocene Epoch, commonly referred to as the Ice Age, represents most of that period, ending about 11,600 years ago. During much of the Ice Age, Ohio’s environment was similar to today with limited geologic deposition occurring mostly in river valleys and during mild seasonal weather patterns. However, there were at least three dramatic periods of geologically rapid change leading to glaciers partially covering Ohio and large loads of sediment being deposited, altering the landscape. Changes in climate during the Pleistocene also affected the plants and animals that lived in Ohio, many of which are no longer found in Ohio today.

Glacial Periods

The three glacial periods that affected Ohio are known as the pre-Illinoian Glaciation, Illinoian Glaciation, and Wisconsin Glaciation.

Pre-Illinoian Glaciation

Before the Pre-Illinoian Glaciation the main river that drained the water on the surface of Ohio was not the Ohio River. The preglacial Teays River, along with its tributaries, carried water out of Ohio. The Teays River had its headwaters in the Appalachian Mountains of North Carolina and flowed through West Virginia and Virginia before entering Ohio where the town of Wheelersburg (Scioto County) now stands. The Teays River flowed north-northwest eventually bending to the west and flowing out of Ohio just south of the town of Willshire (Van Wert County). The entire path of this ancient river and its tributaries was first mapped in Ohio in 1943 by Wilber Stout and has been updated continually by the Division of Geological Survey as new information becomes available.

Map of the preglacial Teays River and Lake Tight in the north-central United States.

During the pre-Illinoian Glaciation, the first advance of ice into Ohio during the Quaternary Period, ice dammed the westward flowing river creating a large lake that covered portions of southeastern Ohio, northern Kentucky, and West Virginia. This lake, known as Lake Tight, breached several ridges along old tributaries to the Teays River and diverted water along the pre-Illinoian ice margin to create the modern Ohio River.

Pre-Illinoian till deposits are only preserved at the surface of Ohio near Cincinnati and across the Ohio River into northern Kentucky, therefore little is known about the full extent and magnitude of this glaciation. Any glacial landforms from this period were either destroyed or buried by subsequent glaciations. However, using the alignment of magnetic minerals preserved in these oldest glacial sediments, including the lake sediment deposited in Lake Tight, geologists have determined that the pre-Illinoian Glaciation occurred during a time when Earth’s magnetic poles were reversed, about 780,000 years ago. After the pre-Illinoian Glaciation, the ice retreated, and conditions remained relatively stable and ice free until the Illinoian Glaciation.

Illinoian Glaciation

The Illinoian Glaciation occurred around 190,000–130,000 years ago across North America. During this time, ice covered all of western, central, and northeastern Ohio. The only portion of the state that remained ice free was southeastern Ohio, likely because the Appalachian Plateau impeded the ice flow. Ice extended into portions of southern and eastern Ohio that appear to have been glaciated only during this single glacial event. In Adams, Brown, and portions of Clermont Counties, glacial deposits associated with the Illinoian Glaciation form a thin, dissected plain directly on top of the underlying bedrock. Streamlined patterns along this dissected till plain and the presence of erratics, like the Gowganda Tillite from the Huronian Super Group, could indicate that Illinoian Glaciers advanced towards the southeast from the Lake Huron area of Ontario. In other portions of the state, a subsequent glacial event has buried or eroded other direct evidence of the Illinoian Glaciation.

In some areas, Illinoian Glacial deposits are capped by a soil called the Sangamon soil. This soil developed after the Illinoian glaciers retreated, about 130,000 years ago. Under the right conditions, the Sangamon soil can be preserved under sediments deposited during the subsequent Wisconsin Glaciation. When advancing ice eroded the upper portion of the Illinoian landscape, the Sangamon soil would also be eroded and reincorporated within Wisconsin Glaciation sediments. In areas where ice never readvanced during the Wisconsin Glaciation, the Sangamon soil can be buried by loess or continually developed into the modern soil under stable conditions.

Wisconsinan Glaciation

The last ice advance into Ohio, the Wisconsin Glaciation, began around 35,000 years ago and ended roughly 12,000 years ago, when ice retreated out of the Lake Erie Basin. Ice reached its maximum extent in Ohio around 26,000–24,000 years ago during a time known as the Last Glacial Maximum (LGM). During this time, glaciers advanced across the landscape in western, central, and northeastern Ohio previously shaped by the Illinoian Glaciation. Like during the Illinoian Glaciation, the Wisconsinan glaciers did not advance into southeastern Ohio. The maximum extent of glaciation during the Wisconsin Glaciation did not advance as far as the Illinoian Glaciation except for in Holmes County. Because the Wisconsin Glaciation was the last glaciation to occur and happened relatively recently, sediments are still well-preserved at the surface across Ohio. Thus, geologists can infer a more detailed account of the events during this period.

During the Wisconsin Glaciation, the Laurentide Ice Sheet extended across Ohio. The glacial lobe split into five parts, or sublobes, because of topographic features that impeded the ice. From west to east, the sublobes were the Miami Sublobe, Scioto Sublobe, Killbuck Sublobe, Cuyahoga Sublobe, and Grand River Sublobe. The split between the Miami and Scioto Sublobes was caused by the Bellefontaine Outlier, an area of resistant Devonian-aged limestone and shale with significant topographic relief surrounded by older, lower-elevation Silurian-aged carbonates.

Depiction of the Laurentide Ice Sheet over Ohio during the Late Wisconsinan Glaciation.

The Bellefontaine Outlier is the highest elevation point in Ohio and represented a significant obstacle for the advancing glacier, which caused ice to flow around the obstacle, rather than directly over it. The Outlier probably split advancing ice during the pre-Illinoian and Illinoian Glaciations into different sublobes, but no direct evidence of this split was preserved after the Wisconsin Glaciation.

The Killbuck, Cuyahoga, and Grand River Sublobes were split from each other by local topographic high points on the Appalachian Plateau. The western edge of the Appalachian Plateau marks the boundary between the Scioto and Killbuck Sublobes in north-central Ohio. The relatively high relief of the Appalachian Plateau likely slowed the advance of the Killbuck Sublobe. The Scioto and Miami Sublobes advances were relatively easier—they faced less topographic impedance, as the area already was flattened by older glaciations, and a bedrock geology with rocks that tend to form flat plains when unglaciated.

As glaciers continued to retreat late into the Wisconsin Glaciation, large glacial lakes began forming from glacial metlwater in northwestern Ohio. These proglacial lakes were the precursor to the modern Lake Erie and developed in sync with the retreat of ice during the end of the Wisconsinan Glaciation in Ohio. As ice continued to retreat northward, lakes formed at progressively lower elevations.

Lake Maumee was the first of these proglacial lakes to develop and had a maximum lake level of 800 feet above mean sea level (m.s.l.). Lake Maumee initially drained through an outlet through the area of Fort Wayne, Indiana, and the Wabash River. Glaciers continued to retreat out of Ohio during the end of the Wisconsinan, eventually leading to lower elevation lake stands—such as Lake Arkona (about 700 feet above m.s.l.) and Lake Ypsilanti (300 feet above m.s.l.). Glaciers then experienced a short readvance around 16,000 years ago, creating Lake Whittlesey at 735 feet above m.s.l. After the development of Lake Whittlesey, glaciers again retreated northward creating lakes at progressively lower elevations—such as Lake Warren (680 feet above m.s.l.). Eventually, ice retreated north of the present-day Niagara River outlet and modern Lake Erie was established with a mean elevation of about 570 feet above m.s.l.

Highest Lake Maumee stage in the Erie basin during the retreat of the Wisconsinan glaciers from Ohio.

Ice Age Environments

Modern Ohio is known for drastic, seemingly seasonal shifts in weather that occur over just a few days, and sometimes within the same day. The story of glacial advance and retreat in Ohio during the Quaternary Period mimics these trends, only on larger timescales. The presence of large continental glaciers in Ohio was a result of natural fluctuations in global climate owing to changes in Earth’s orbit. Variations in how Earth rotates, tilts, and wobbles affect how much energy from the sun is absorbed by the planet and changes global average temperatures (learn more).

These changes are cyclical and occur on different timescales; however, these cycles align to create conditions perfect for glaciers. For the past million years Earth has experienced major glaciation events about every 100,000 years, with the last Ice Age reaching a maximum around 24,000 years ago and the penultimate Ice Age occurring about 130,000 years ago. These changes in climate affected all aspects of the past environments in Ohio, including the plants and animals that thrived here.

Plant Life

Scientists can study plants that were native to Ohio during glaciation by studying pieces of wood, leaves, seeds, and even pollen preserved within sediment deposited by glaciers. Most of the wood preserved in glacial sediments comes from spruce and pine trees. Some of these pieces of wood include tree stumps that were buried in place near Cincinnati, providing direct evidence that spruce trees were native to Ohio and not just transported from farther north. Spruce and pine needles are commonly found in association with woody material in glacial materials. These materials tell us that trees like spruce, fir, cedar, and hemlock—which today are common in northern environments like Canada—were commonplace in Ohio at the height of glacial events.

Pollen from these trees was blown by wind and typically was best preserved in lakes that existed during glacial times. These microscopic pollen spores can be identified and counted under a microscope to determine relative percentages of how much of an environment was composed of certain plant or tree types. Studies of pollen in Ohio consistently shows a gradual shift from more coniferous tree pollen types (spruce and pine) to more deciduous tree pollen types (oak and elm) around 12,000–10,000 years ago. This transition of native flora likely occurs cyclically moving between glacial and interglacial periods during the Quaternary Period. However, there are microclimatic conditions in certain places of Ohio, like Hocking Hills and Cedar Bog which can support similar plant life to what would've been found in Ohio during glacial periods. These locations experience cooler than average temperatures allowing these plants to thrive.

Animal Life

Similar to the history of plants in Ohio, the native species of animals drastically changes from glacial to interglacial periods. During glacial periods, animals must have adapted to colder-than-average temperature conditions year-round or migrated south to warmer climates. During glacial periods, animals such as mammoth, mastodon, musk ox, caribou, peccary, short-faced bear, elk-moose, ground sloth, and giant beaver roamed Ohio. All these species are either now extinct or found outside of Ohio in more suitable habitats. Some animals, such as white-tailed deer and other mammals, were suited to life in Ohio throughout the Quaternary Period. Some archeological evidence suggests that humans lived in Ohio near the end of the Wisconsin Glaciation. Tool marks on mammoth and mastodon skeletal remains indicate that animals were butchered by humans, and some of these flint tools have been recovered from dig sites near megafauna skeletons.

Artist depiction of mastodons roaming Ohio during the last Ice Age. Illustration by Jim Glover.