Weathering Along the NCIT EarthCache

At the posted coordinates, you'll see this sandstone mile marker - the subject of this EarthCache!

What is Weathering?

Over time, even the hardest rock yields to the forces of nature. The process by which rocks break down and decay is known as weathering, and it plays a critical role in shaping Earth's surface. Unlike erosion, which involves the movement of rock particles, weathering occurs in place, gradually altering stone through physical forces, chemical reactions, and biological activity.

There are three primary types of weathering: physical (mechanical), chemical, and biological. Often, these processes act together, weakening and reshaping rock formations over thousands—or even millions—of years.
 

Physical (Mechanical) Weathering

Physical weathering, also known as mechanical weathering, is the process by which rocks break into smaller pieces without any change to their chemical composition. It typically occurs due to temperature changes, pressure release, or mechanical forces like water, wind, or ice. One of the most common examples of this type of weathering is freeze-thaw action, where water seeps into cracks in rock during warmer weather, then freezes as temperatures drop. Since ice expands when it freezes, it exerts pressure on the rock, widening the crack. Repeated cycles can eventually split the rock entirely.

Another form of mechanical weathering comes from thermal expansion and contraction, especially in environments with large temperature swings, such as deserts or exposed mountain faces. As the surface of the rock heats during the day and cools at night, it expands and contracts, which causes outer layers to loosen and eventually peel away in a process called exfoliation. In addition, physical abrasion from wind carrying sand, glaciers dragging embedded rock fragments, or fast-flowing rivers tumbling stones can physically grind down surfaces. The results are often visible as jagged fragments, sharp edges, or even rounded pebbles smoothed by water.
 

Chemical Weathering

Chemical weathering involves the alteration of the internal chemical structure of minerals in rock, changing them into new, usually softer and less stable substances. This process is especially effective in warm, humid environments where water is abundant. One of the primary mechanisms is hydrolysis, in which minerals like feldspar (common in granite) react with water to form clay. Over time, this reaction weakens the rock and can create soft, chalky surfaces or residual clay deposits.

Another common chemical process is oxidation, in which minerals containing iron react with oxygen in the air or water to form rust-like compounds. This often gives the rock a reddish or yellow-brown stain and makes it more brittle. You may notice this type of weathering on rocks with a rusty surface or crumbly, oxidized edges. Carbonation is also widespread, particularly in regions with limestone or marble bedrock. Slightly acidic rainwater (due to dissolved carbon dioxide) reacts with calcium carbonate in these rocks, gradually dissolving the stone and leaving behind pitted surfaces, rounded cavities, or even small sinkholes.
 

Biological Weathering

Biological weathering is caused by the actions of living organisms, which can either physically break rocks apart or chemically alter them through metabolic processes. One of the most direct examples of this is root wedging, where the roots of trees or plants grow into small cracks in rocks in search of water or stability. As the roots expand, they exert pressure on the rock, widening cracks and eventually causing pieces to break off. You’ll often see this at rocky outcrops where trees cling to cliff faces or sidewalks where weeds break through pavement.

In addition to mechanical effects, biological organisms also contribute to chemical weathering. Lichens and mosses, for example, often colonize rock surfaces and secrete weak acids that slowly dissolve the minerals they cling to. Over time, this can soften the rock surface beneath them, leading to uneven pitting or discoloration. Even microscopic organisms in soil can produce organic acids that leach into bedrock and contribute to its slow breakdown. In some cases, animal activity—like burrowing or digging—can expose fresh rock surfaces to the air and moisture, accelerating other weathering processes.

About the North Coast Inland Trail

The North Coast Inland Trail (NCIT) is a 12-foot-wide, asphalt paved trail built over the abandoned Toledo, Norwalk, and Cleveland Railroad and spans nearly 100 miles across northern Ohio, from Lorain to the Toledo area with some sections still being built. In 1992, seven park districts agreed to develop a system connecting trails in northwest Ohio, each managed by local jurisdictions. The NCIT is the result. The Lorain County Metro Parks’ portion runs from Lake Erie in Lorain to the county line in Wakeman, passing through Elyria and Oberlin along the way.

The Toledo, Norwalk, and Cleveland Railroad was constructed in 1851 and served as a vital link between Chicago and Cleveland. This rail line lead to the founding of several small villages including Kipton. In 1866, the Lake Shore and Michigan Southern Railroad built a line from Elyria to Oberlin which then continued west using the Toledo, Norwalk, and Cleveland Railway (which you're standing on right now). These railways allowed for the expansion of businesses, agricultural interests, and several cities along its route including Oberlin and Elyria. The railroad hauled freight, lumber, coal, produce and passengers to and from the rich farmlands of this region until its abandonment in 1975. The TN&C Railroad also constructed numerous stone mile markers, which can be found along many parts of the NCIT!

This EarthCache is placed with permission from Lorain County Metroparks - Permit #14521