Editorial: A volcanic history of the Granite State

  • A lava flow advances down a road in the Leilani Estates subdivision near Pahoa on the island of Hawaii on May 7. AP

Wednesday, May 16, 2018

Like millions, we watched with horror and fascination as the slowly moving black-and-Halloween-orange blob devoured a car and set everything in its path ablaze. Pele, the fire goddess who in religion and lore lives in Hawaii’s Kilauea volcano, is demonstrating her power. The lake of molten lava that filled the volcano’s crater has been falling as it spews out of cracks in two residential neighborhoods on the chain’s biggest island. Any day now, volcanologists say, rocks from the walls of the crater could collapse and form a plug that allows steam to build up, setting the stage for a massive explosion.

Meanwhile, fans of apocalyptic endings are buzzing about the hundreds of earthquakes that have been shaking Yellowstone National Park and causing a long-dormant geyser to erupt. Yellowstone, it seems, is one giant supervolcano. Its eruption could conceivably spew enough ash into the atmosphere to cause an ice age. Not to worry, the U.S. Geological Survey reports. The odds of its eruption in any given year are 1 in 730,000 and Western states should be safe for at least the next 1,000 years.

Could something like that happen here in New Hampshire? It already has, but humans weren’t around to see it.

The Granite State is home to at least two extinct volcanoes. Most people live, visit or pass through them unaware that deep below, the earth once bubbled beneath their feet. One of the ancient volcanoes is even famous in geological circles: the Ossipee Ring Dike. Its eroded mountains formed the cone of a volcano believed to have been about 10,000 feet tall. The volcano erupted some 100 million years ago and again 10 million years later. Today, the tallest peak left, at just under 3,000 feet, is Mount Shaw.

The towns of Ossipee, South Tamworth, Tuftonboro and Moultonborough are on the rim. In the center of the circular mountain range is the Ossipee caldera, the filled cauldron of the collapsed volcano.

The ring dike has been much studied. The late New Hampshire state geologist Eugene Bourdette once called it “the most accessible, exposed and vivid example of the inner workings of a volcanic system.” It draws geologists and their students from the world over. Its circular layout can be seen from Castle in the Clouds and from a boat on 180-foot deep Dan Hole Pond. The pond fills what was once a vent on the side of the volcano.

New Hampshire’s volcanic history is responsible for the wealth of crystalline minerals, some semiprecious or precious, that can be found in the Ossipee Range. Within its once-molten granite can be found topaz, tourmaline, amethyst, garnet, beryl (the state mineral) and smoky quartz (the state gem).

Pawtuckaway State Park is at the center of another, much smaller volcanic ring dike. It’s sometimes referred to as the Dragon’s Eye because it’s in the middle of concentric rings of mountains formed by magma that rose up from a hot spot deep below.

The earth beneath the Granite State has cooled. The winters are still harsh, the mosquitoes and black flies biting, and nor’easters still rattle the windowpanes, but no red-hot lava creeps over the landscape. Those days are behind us.