We think of a marble tombstone marking our loved ones' graves forever, but even stone can erode over time. British researcher Rob Inkpen has found that weather has eroded spots on some century-old gravestones by more than 1 inch. Over time, even if the gravestone endures, the inscriptions may fade until they're illegible.
Tombstones are a popular subject for both classroom studies and serious geological research. Inkpen says online that tombstones are a convenient tool for studying and measuring how different types of rock erode over centuries, and how erosion in one part of the country compares to another.
Inkpen lists several methods for studying weathering: The rate at which the lead lettering placed in old gravestones has worn away; how much the upper gravestone has eroded compared to the base; deterioration in the carved letters; and a detailed photographic analysis of the surface.
The effect of weathering depends on the material of the tombstone, the environment and the form the weathering process takes. Exposure to different climates or forms of pollution can cause flaking, pitting, the growth of lichen or the development of black deposits on the stones.
The environmental group Evergreen reports that granite is resistant to chemical weathering, but marble, which is soluble, weathers faster in acid rain. Sandstone and quartz are more durable than marble, but Inkpen says sandstone is likely to shed flakes as it weathers.
Pollution can increase weathering, and the weathering of tombstones can be used to measure pollution. Geomorphologist Tom Meierding told National Geographic News that he's found many tombstones supposedly weathered by acid rain were actually affected decades earlier, before anti-pollution laws began to clean our air.
Weathering also varies with the tombstone's environment. A given cemetery may be urban or rural, on the coast or in a sandy desert or forest. Even within the graveyard, the environment may vary from tombstone to tombstone: A tree may provide shelter from the weather, or water may flow over the tombstone bases at different rates depending on the slope of the ground.
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