The Big M overlooking Butte celebrated its 98th birthday last month, on a hill born millions of years ago.
In late May 1910, a couple weeks after Congress established Glacier National Park, engineering students from the Montana School of Mines built a 67 feet tall and 75 feet wide letter M on the southeast slope of Big Butte.
The letter was designed by a surveying party from the school, a day before the student body turned out to complete the project.
“The great hill seemed alive with swiftly moving figures,” states a May 29, 1910, article in The Montana Standard. “From 10 o’clock in the morning until five that night the boys labored as few of them have labored before …” Big Butte and its M would have little fanfare for more than 50 years until May 2, 1962, when students and alumni completed a project to light the symbol.
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Then Gov. Tim J. Babcock led several hundred onlookers in a countdown to light the 90 feet by 90 feet letter at 9:30 p.m.
The project added 150 lights totaling 5,280 watts to give the venerable old letter a bright new look, according to news reports.
“A tremendous roar went up from the huge gathering as the lights on the slope of Big Butte shot into brilliance, accompanied by the loud report of a bomb set off atop the peak’s summit,” The Montana Standard reported.
While the history of the Big M is easily tracked through historical records, the butte on which it sits is less telling.
Rocks on the 6,299-foot Big Butte date back some 50 million years, and while two Butte geologists agree it was formed from molten lava, they disagree on the intensity of the butte’s birth.
Dick Berg, senior research geologist with the Bureau of Mines and Geology at Montana Tech, believes Big Butte is the remnants of a “vent complex.” “It’s definitely rock that formed by cooling of magma,” he said. “No doubt about it.” His theory is magma rose to the surface and perhaps erupted or oozed onto the surface to cause lava flows, but not to the magnitude of a volcano.
Hugh Dresser, who retired as a professor of geology from Montana Tech in 1998 after 33 years, sees it differently.
“It’s an extinct rhyolitic volcano,” he said. “It put out ash-flow tufts, which are high-velocity flows of ash.” While Big Butte today is an ideal location for a relaxing walk, it would have been a dramatic site 50 million years ago, Dresser said.
Ash-flow tufts form when gas-filled lava reaches the surface and explodes while traveling across the ground at speeds over 100 mph, he said.
Dresser, who wrote a 75-page handbook in 2000 on Big Butte volcanics, said evidence of very thick, viscous flows are present on Big Butte.
On the southwest side of the hill, Dresser said a knob — which he calls a “parasitic funnel-shaped vent” — emerged after the main flow of magma plugged.
Pressure from the main flow blew out the side of the butte leaving behind what appears today as a knob.
“That is one of the last (volcanic) events that occurred,” he said.
It’s unknown how long Big Butte would have been an active volcano, but Dresser thinks it occurred over a few thousand years.
Reporter Justin Post may be reached via e-mail at justin.post@lee.net.
