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Why does Virginia have volcanoes?

The Shenandoah Valley of Virginia is a destination for many visitors to the Commonwealth. It is hard for people to imagine such a peaceful scene could have been born out of a fiery birth.
The Shenandoah Valley of Virginia is a destination for many visitors to the Commonwealth. It is hard for people to imagine such a peaceful scene could have been born out of a fiery birth.

Virginia is known for having the first English colony in the New World, as well as being the Mother of Presidents. The Shenandoah Valley and the Blue Ridge Parkway, along with our beautiful beaches bring visitors from all across the nation and overseas.

Trimble Knob is southwest of Monterey in Highland County, Virginia,

But a history of a volcanic past? It may seem strange, but it's true. Virginia is one of the few East Coast states that can make this claim. Virginia has two very ancient and prominent examples of these volcanoes that can still be seen today.

There is still evidence of the lava flow to be seen in fractures and cracks in the Earth's surface, testament to volcanic activity about 48 million years ago at Trimble Knob, in Highland County (near the West Virginia line), and Mole Hill, near Harrisonburg.

Both Trimble Knob and Mole Hill are the remains of long extinct volcanoes that geologists call "plugs." The two sites are totally different from each other, with Trimble Hill being small, stubby and almost treeless. Mole Hill in much higher, 1,900 feet above sea level, almost like a small mountain, and covered with thick brambles and forest.

Visitors can still see basalt rocks, an indication of their fiery origins, interspersed throughout the green sedimentary rocks dominating the Shenandoah Valley landscape. Between 47 million and 48 million years old, these volcanoes are considered infants in any state East of the Mississippi River. Both volcanoes are on private property, and access is limited, keeping most tourists away.

Geologic history of Virginia's volcanoes

What has puzzled geologist for years is the time span between the last volcanic eruptions in Virginia and the earlier eruptions that occurred 150 million years ago when the super-continent, Pangaea broke up. The stretching of the Earth's crust allowed huge volumes of magma to escape from the mantle.

What perplexed scientists was that on the East Coast, there are no rifts or colliding tectonic plates that would give birth to volcanoes or create earthquakes as occurs on the West Coast. Geologists say the lack of this kind of activity puts the East Coast in a "passive margin."

At first, scientists thought the Virginia volcanoes were the result of "hotspots," plumes of magma that rise up through the mantle. This is the accepted theory on the formation of the volcanic chains in Hawaii and Yellowstone National Park. But Virginia's volcanoes didn't meet the criteria. Something was different.

Recent study of Virginia volcanic activity

In a study published in Live Science's Our Amazing Planet, a team of scientists analysed rocks from the areas where the Virginia volcanoes are located. "These young volcanoes are in an area where no one would expect to see volcanic activity," said lead study author Sarah Mazza, a geologist at Virginia Tech. "These rocks are our only physical window into processes that helped shape Virginia and even the whole southeastern Appalachia as well."

The study found out three things that made Virginia's volcanoes unique. First, the magma temperature was too low, almost 300 degrees lower that what would be found in a hotspot, (2,570 degrees Fahrenheit, rather than the 2,732 F). Second, the magma source was too shallow for a hot-spot volcano.

The third and most significant finding was the date of the eruptions. The team was able to date the eruptions of the Virginia volcanic sites precisely at 47 million to 48 million years ago. This is 10 million years after the last hotspot passed through. "That difference is significant enough for us to think this hotspot probably wasn't the case," Mazza said.

In the process of examining the rocky remains, the team discovered the Virginia lava is the chemical cousin of eastern Atlantic volcanoes, because their sources are both buried leftovers from the breakup of Pangaea, the supercontinent. "The upwelling is allowing these [Virginia] volcanoes to sample a part of the mantle that is also seen over in the eastern part of the Atlantic," Mazza told Live Science's Our Amazing Planet.

Mole Hill and Trimble Knob are not mentioned in any tourist pamphlets, and very few people even realize they have seen the remains of a volcano when driving by Mole Hill. One interesting fact about Mole Hill is found in historic texts. It is said that locals celebrated the end of the War of 1812 by having a barbecue at the top of Mole Hill, where an ox was roasted.

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