Virginia is often associated with its rich history and scenic landscapes, but it also has a surprising geological feature: volcanoes. Despite being known for its passive margin geology, where volcanic activity is rare, Virginia has a few volcanic remnants scattered across its landscape.
Among these, Mount Rogers stands out as the highest point in the state, formed from lava that erupted 750 million years ago during the breakup of the supercontinent Rodinia. However, the largest volcano in Virginia is not Mount Rogers but Mole Hill, located west of Harrisonburg in Rockingham County.
Mole Hill: The Youngest Volcano in the East
Mole Hill is a rounded hill composed of basalt, a volcanic rock, formed during the Eocene epoch of the Paleogene period, approximately 47 million years ago. It is one of the youngest volcanoes on the east coast of North America and is considered an eroded remnant of what was an active volcano.
The peak of Mole Hill stands at approximately 1,893 feet (577 meters) above sea level, making it a significant geological feature in the region.
Geological Significance
The basalt at Mole Hill is unique, with a dark greenish gray to grayish black color, medium grain size, and moderate porphyritic texture. It is an olivine-spinel basalt with abundant large pale green pyroxene and minor yellow-brown olivine phenocrysts.
This type of basalt intrudes through the Ordovician Beekmantown Group of carbonate rocks, indicating its volcanic origin.
Historical Context
Initially, geologists thought the rocks at Mole Hill were of Paleozoic age, but radiometric dating in 1969 revealed they were much younger, dating back to the Eocene epoch. This discovery placed Mole Hill among the youngest volcanic features in the eastern United States.
The area around Mole Hill also contains other geologically similar features, such as Trimble Knob in Highland County and intrusive igneous rocks near Ugly Mountain in Pendleton County, West Virginia.
Erosion and Formation
Over millions of years, erosion has chipped away at the volcanic features, leaving behind the cone-shaped magma conduit that served as the volcano’s plumbing.
The basalt at Mole Hill erodes more slowly than the surrounding limestone, making it a prominent feature in the landscape. Today, Mole Hill stands as a testament to the region’s volcanic past, offering a glimpse into the geological history of Virginia.
Conclusion
Virginia’s volcanic past is a fascinating aspect of its geology, and Mole Hill is a prime example of this. Despite being one of the youngest volcanoes in the eastern United States, Mole Hill is now considered extinct, with no significant risk of future eruptions.
However, its presence highlights the dynamic geological processes that have shaped the state’s landscape over millions of years. For geologists and enthusiasts alike, Mole Hill remains a significant and intriguing feature in Virginia’s geological landscape.