Utah has a volcanic history far younger than many might expect. It's possible that as recent as six centuries ago — the end of the Middle Ages — the Beehive State had some real hot spots. Some of this volcanic activity also has potential for future eruptions.

Focal point of much of this volcanic activity was the Fillmore area, also known as the territorial capital of the state. The Ice Springs cinder cones and lava flows in the Flowell area, four miles west of Fillmore, are among the youngest of volcanic rocks in Utah.

"These are certainly less than 1,000 years old and maybe as young as 600-800 years old," said Barbara Nash, professor of geology and geophysics at the University of Utah.

Seventeen miles northwest of Fillmore is also Pahvant Butte, a "basaltic tuff cone" that rises some 850 feet above the valley floor. Pahvant, the valley's landmark and namesake, is also believed to have erupted under the surface of ancient Lake Bonneville, 15,300 to 16,000 years ago. Shoreline markings of Utah's ancient inland sea are clearly visible on Pahvant.

"I think it would have looked glorious," Nash said of Pahvant sparking up hundreds of feet above Lake Bonneville during one of its deepest water levels, like some underwater volcano in the Hawaiian Islands.

Although certainly nowhere near as potentially hazardous as a Mount St. Helens or a Mount Rainier, because Utah's recent volcanic activity wasn't explosive, the Black Rock Desert area could still reignite one day. Like Wasatch Fault earthquake dangers, no one can predict their future, though.

"Based on past history, the Black Rock Desert has the potential for another eruption, although there is no evidence that one is imminent," Nash said. "Any similar eruption would not pose a serious hazard to residents of the area because they have not been either large in volume or explosive in style.

"An eruption similar to the one that formed Pahvant Butte would deposit several inches of dark volcanic ash in Fillmore and surrounding communities, and there could be local lava flows emanating from the volcanic vent," she said.

Some locals still call Pahvant Butte "Sugarloaf Mountain" in reference to its shape. Pahvant is also sometimes spelled Pavant like the nearby valley and means "water people" among local Indian cultures. A 1927 attempt to build a wind-powered generator on the north flank of Pahvant is also still visible.

A dirt road, passable by car, traverses the Black Rock Desert between Fillmore and Clear Lake.

Tabernacle Hill, another cinder cone named for its shape, is located a few miles west of Meadow and southwest of Fillmore. Nash said eruptions there happened in the shallow waters of Lake Bonneville during its "Provo" level, some 400 feet less than the Bonneville shoreline stage, about 14,320 years ago.

Carbon dating is the source of many of these time estimates.

Lake Bonneville was a huge inland sea along much of the Wasatch Front, as big as Lake Michigan and a lot deeper at 1,050 feet in some places, though shallower near Fillmore. The lake was 346 miles long; 145 miles wide and went as part south as Pine Valley Mountains and as far north as the Preston, Idaho, area.

The GSL, Utah Lake, Rush Lake and Little Salt Lake are all remnants of Lake Bonneville.

Other portions of Utah in the Snow Canyon area of Washington County and the area south of Cedar Breaks National Monument also have strong volcanic histories. Some are cinder cones; others are vents.


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