Describing Donnelly Dome

Behind Donnelly Dome, Pipeline Mile 560--When I bump off the mosquitoes, the front screen of the tent provides a clear view of a favorite Richardson Highway landmark--Donnelly Dome. I camped near the Donnelly Dome reflection pond to get acquainted with the mountain, which from here looks like a 3,910-foot loaf of stone with green stubble on the bottom third.

Standing alone in the Delta River Valley 18 miles south of Delta Junction, Donnelly Dome always sparks a few questions by those who drive past; I've heard people muse over whether the Dome is a lonely volcano.

Before I took my dog for this long walk, I called Tom Buntzen to find out the facts about Donnelly Dome.

Buntzen is a state geologist with the Alaska Division of Geological and Geophysical Surveys. Donnelly Dome is a bit odd, he said. In fact, it shouldn't even be here.

"It is out of place," he said. "A glacier went down the (Delta River) valley. It should have sheared Donnelly Dome off, but it didn't."

There's a word for bumps like Donnelly Dome, Buntzen said: "Donnelly Dome is a fleigberg."

Come again?

"A fleigberg," Buntzen repeated. "A mountain that has been overridden by ice."

Buntzen has climbed to the top of the dome and has seen evidence that glaciers touched it, even if they didn't shave it from the valley floor. Buick-sized "erratics," rocks that came from somewhere else, sit on top of the dome.

"They were conveyor-belted out on the ice and dropped on top of Donnelly Dome," Buntzen said.

How did the dome resist being scraped from the earth while those around it crumbled under the force of an Alaska Range glacier that covered the area 70,000 to 100,000 years ago? Buntzen said Donnelly Dome may have had the luck to squeeze between two separate tongues of the glacier.

"And there was another glaciation that just missed it," Buntzen said. "In the Donnelly Glaciation, from 30,000 to 10,000 years ago, glaciers reached just to the base of the dome, but they didn't cover it."

I'm glad. Someday I'll climb my favorite fleigberg. But not today, I'm too tired.