Olentangy River Banks EarthCache

Highbanks Metro Park, located in Columbus, Ohio, is known for its dramatic landscapes shaped by ancient geological forces. The park sits atop Devonian shale bedrock, formed over 370 million years ago when Ohio was covered by a shallow sea.

One of the park’s highlights is the Overlook Deck, which provides a stunning view of the Olentangy River and its contrasting riverbanks. On the near side, steep shale cliffs drop sharply to the water, shaped by constant erosion. Meanwhile, the opposite bank is much lower and flatter, formed by the gradual buildup of sediment over time.

This overlook is also a prime bald eagle viewing spot. The park’s towering trees and proximity to the river provide an ideal habitat for these majestic birds, which can often be seen soaring overhead or perched along the riverbanks.

This EarthCache explores how the river’s flow creates these striking differences, highlighting the natural forces of erosion, deposition, and river meandering that continue shaping the landscape today.

Why is One Side of the Olentangy River Steep and the Other Flat?

1. The Role of Bedrock: Devonian Shale and Ohio’s Geological Past

The steep bank near the Overlook Deck is primarily made of Devonian-age Ohio Shale, a soft, grayish-black rock that formed around 370 million years ago when Ohio was covered by a shallow tropical sea. Over time, layers of organic material settled at the sea bottom, forming the shale we see today.

• Why is shale important here?
  Shale is relatively soft and prone to erosion, but when it forms cliffs, it does so in a way that creates sheer, vertical faces because it tends to break apart in thin, stacked layers. This is why you see a steep drop-off along the overlook side of the river.

2. The Impact of Glaciers: Why the Land is Uneven

Fast forward to about 20,000 years ago, when the last Ice Age was ending. Huge glaciers, more than a mile thick, covered much of Ohio. These glaciers scraped and flattened large portions of the landscape while also depositing sediments as they melted.

• The glaciers left behind a mix of till (a mix of clay, silt, sand, and rocks) on the flatter east bank of the river.
• On the west bank, erosion by meltwater and the Olentangy River gradually cut into the bedrock, creating steep cliffs.

This explains why the overlook side of the river has steep shale walls (exposing ancient bedrock), while the opposite side is a low, rolling floodplain (formed by glacial deposits and river sedimentation).

3. River Evolution: Why the Olentangy Has Two Different Banks

Rivers are constantly changing their paths due to erosion (wearing away land) and deposition (building up new land). The Olentangy River follows a classic meandering pattern, where one side experiences more erosion while the other side accumulates sediment.

• The overlook side (west bank) is the "cut bank" where the river actively erodes into the shale cliffs, making them steeper over time.
• The opposite bank (east side) is the "point bar" where the river slows down and deposits sediment, making it much lower and flatter.

Over thousands of years, this process continues shifting the river, deepening the contrast between the two banks.

The Opposite Riverbank: Understanding Point Bars and Floodplains

While the overlook side of the Olentangy River has steep shale cliffs due to erosion, the opposite bank is much lower and flatter. This is because it’s part of a point bar—a landform created by the natural process of river meandering. Let’s break it down:

1. What is a Point Bar?

A point bar is a gently sloping deposit of sand, gravel, and silt that forms on the inside of a river bend. This happens because water moves slower on the inner curve of a meander, causing sediment to settle and accumulate over time.

• Imagine a river as a moving conveyor belt of water and sediment.
• On the outer bend, fast-moving water erodes the bank (cut bank).
• On the inner bend, slower-moving water drops off sediment, gradually building up a point bar.

Over centuries, this process can create broad, flat floodplains on the inside of the bend, like the one you see across from the overlook.

2. The Role of Flooding in Point Bar Growth

Point bars grow slowly over time, but during floods, the process speeds up. When the river overflows, it spreads sediment across the low-lying floodplain, depositing new layers of silt and sand.

• This is why floodplains often have rich soil—they’re built from centuries of nutrient-rich sediment being deposited.
• Farmers historically settled near floodplains for this reason, but these areas are also more prone to flooding.

If you were to dig into the soil on the opposite bank, you’d likely find layers of sand, silt, and clay—evidence of past floods and sediment buildup.

3. How the River Changes Over Time

Because of erosion on one side and deposition on the other, rivers slowly shift their course over time. This process, called meander migration, means:

• The cliffside (cut bank) gets steeper and moves back as erosion continues.
• The point bar (flat side) grows outward as more sediment is deposited.

Over thousands of years, the Olentangy River has likely shifted its course many times, carving out different paths through the landscape. If the river continues this pattern, the overlook side will keep eroding while the opposite bank expands and becomes even flatter.