Fastly Fading EarthCache

When someone is buried, it is customary to place a grave marker at the burial site. Many people assume these markers will last forever, but a walk through any cemetery shows otherwise. Some markers have become difficult to read due to weathering, a natural process that breaks down rock through physical, chemical, and biological forces.

Weathering occurs due to the effects of rain, wind, temperature changes, and biological activity. Over time, these forces wear away the stone, causing inscriptions to fade and surfaces to roughen. Cemeteries are an excellent place to study weathering because the date on a headstone provides a time reference, allowing researchers to estimate how much weathering has occurred over a given period.

Weathering in Nebraska’s Climate

Nebraska’s climate plays a significant role in the weathering of cemetery headstones. The state experiences a humid continental climate with hot summers and cold winters. The region is subject to frequent freeze-thaw cycles, especially in winter and early spring. These cycles contribute to frost wedging, a type of mechanical weathering where water enters cracks in the stone, freezes, expands, and eventually breaks the stone apart.

Strong winds, common in Nebraska, contribute to abrasion by carrying dust and sand particles that slowly erode stone surfaces. Nebraska also experiences periodic droughts and high evaporation rates, which can lead to salt crystallization, a chemical weathering process that occurs when dissolved salts in groundwater form crystals and expand within the stone’s pores.

Biological weathering is also present, as lichens and mosses thrive on older, shaded gravestones, breaking down the rock surface over time. Acid rain from industrial pollution may contribute to chemical weathering, particularly on limestone or marble headstones, which dissolve more easily in acidic conditions.

Types of Weathering in the Cemetery

    1.    Mechanical Weathering: Includes frost wedging from freeze-thaw cycles, rock abrasion from wind-blown sand, and thermal expansion due to Nebraska’s temperature fluctuations.
    2.    Chemical Weathering: Includes acid rain dissolving calcite in limestone or marble headstones and oxidation causing rust-colored staining on certain rock types.
    3.    Biological Weathering: Includes lichen and moss breaking down minerals in the stone and tree roots causing fractures.

Identifying Different Types of Weathering on Cemetery Headstones in Nebraska

Cemeteries in Nebraska often contain headstones made from materials such as limestone, marble, granite, and sandstone, each of which weathers differently due to the state’s climate conditions. Understanding how these stones respond to environmental factors can help geocachers identify the type of weathering at work.

1. Identifying Mechanical Weathering

• Frost Wedging (Freeze-Thaw Cycles):
• Look for cracks and fractures, especially in older limestone and sandstone headstones.
• Pieces of stone may be missing, creating jagged or split surfaces.
• Most common in limestone, sandstone, and marble, which are more porous and allow water to seep in before freezing.
• Thermal Expansion and Contraction:
• Seen as small surface cracks or flaking on headstones.
• More likely on granite due to its dark color, which absorbs heat during the day and rapidly cools at night.
• Can cause the outer layers of stone to weaken over time.
• Abrasion (Wind and Sandblasting):
• Look for rounded edges and smoother surfaces on exposed headstones.
• Can make inscriptions faint or illegible over time.
• Most noticeable in sandstone and softer limestone, as these rocks erode more easily when exposed to wind-driven dust and debris.

2. Identifying Chemical Weathering

• Dissolution (Acid Rain):
• Most obvious on limestone and marble headstones, which contain calcite that dissolves in weak acids.
• Look for smoothing of inscriptions, making older lettering difficult to read.
• Surface may appear pitted or rough where acid rain has dissolved the stone unevenly.
• Oxidation (Rusting of Iron Minerals):
• Found in headstones with iron-bearing minerals, such as some sandstones and granites.
• Appears as reddish-brown staining or a rusty crust on the stone’s surface.
• More common in stones with iron-rich components, especially when exposed to moisture.
• Salt Crystallization (Salt Wedging):
• Occurs when water containing dissolved salts seeps into a porous stone and then evaporates, leaving salt crystals behind.
• Creates a flaky, powdery texture on the stone surface.
• Most common in limestone and sandstone, particularly in dry periods when evaporation rates are high.

3. Identifying Biological Weathering

• Lichen and Moss Growth:
• Look for green, gray, or black patches on the surface of headstones.
• Lichens secrete weak acids that dissolve the stone over time, causing small pits or rough textures.
• Common on limestone, marble, and sandstone, where moisture helps lichens grow.
• Root and Plant Damage:
• Tree roots growing near graves may cause shifting or cracking of stones.
• Small plants or weeds growing in cracks can widen them over time.
• Can occur in any type of stone but is especially problematic for soft, porous rocks like limestone and sandstone.

How to Identify Common Headstone Stones
    1.    Granite

• Look For: Speckled appearance with grains of quartz, feldspar, and mica; comes in a variety of colors (gray, pink, black, red).
• Feel: Very hard and coarse; resists scratching.
• Weathering: Minimal—inscriptions usually remain sharp for decades.

    2.    Marble

• Look For: Smooth, sometimes with light gray or blue veining; often white or light-colored.
• Feel: Soft and smooth to the touch; you can scratch it with a knife.
• Weathering: Wears down over time—inscriptions may become difficult to read after decades due to acid rain and surface erosion.

    3.    Limestone

• Look For: Dull, chalky appearance; usually tan, gray, or cream.
• Feel: Softer than granite; easily scratched or worn.
• Weathering: Prone to chemical weathering—inscriptions fade and surfaces may flake.

    4.    Sandstone

• Look For: Visible sand grains; layered or banded in appearance; earthy colors (red, brown, tan).
• Feel: Grainy texture; may crumble with time.
• Weathering: Often shows deep pitting and uneven surfaces.

    5.    Slate

• Look For: Flat, smooth, and usually dark gray, green, or purplish; can split into thin sheets.
• Feel: Smooth, fine-grained surface.
• Weathering: Surface may delaminate or flake, especially in freeze-thaw climates.

By carefully observing the signs of weathering, geocachers can determine which natural forces have shaped each headstone. Combining knowledge of Nebraska’s climate with these weathering characteristics makes for an insightful geological study at this historic cemetery.

Please be respectful of the cemetery and its visitors. Enjoy your exploration of the geological processes at work!