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. People have been heard to muse over whether the Dome is
a lonely volcano.
Donnelly Dome is a bit odd. In fact, it shouldn't even be here. It
is out of place.Thousands of years ago, A glacier went down the
(Delta River) valley. The glacier should have sheared Donnelly Dome
off, but it didn't.
There's a word for bumps like Donnelly Dome. Donnelly Dome is
a fleigberg.
A fleigberg is a mountain that has been overridden by ice. There is
evidence on the top of the dome 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. The
erractics were conveyor-belted out on the ice and dropped on top of
Donnelly Dome.
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? 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. In
the Donnelly Glaciation, from 30,000 to 10,000 years ago, glaciers
reached just the base of the dome and did not cover it.
Once overlain by glaciers, the geology around Donnelly Dome is
marked by glacial moraines as well as alluvial deposits from the
Delta and Tanana Rivers. Numerous mineral deposits are found in the
vicinity of Delta Junction ranging from gold to molybdenum to coal.
Donnelly Dome was formed as a glacier coming from the Alaska Range
split in two, carving away sides of a former mountain.
The trail head and parking for Donnelly Dome trail is at N63 46.428
W145 45.723.
To get credit for this EC, post a photo of you with GPS and
Donnelly Dome in the back ground, or if you are up to the challenge
hike to the top of the dome and take your picture up there. The
picture can be from the trail head or on top of Donnelly Dome.
Please answer the following questions.
1. What is the elevation at trail head?
2. What type of stone are most of the Erratics laying around
Donnelly Dome?
3. How many years ago was the Donnelly Glaciation
period?
| Cav Scout has earned GSA's highest
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Do not log this
EC unless you have answered the questions and have a picture ready
to post! Logs with no photo of the actual cacher (human face
included) logging the find or failure to answer questions or
negative comments will result in a log deletion without notice.
Exceptions will be considered if you contact me first (I realize
sometimes we forget our cameras or the batteries die). You must
post a photo at the time of logging your find. If your picture is
not ready then wait until you have a photo.
Sources of
information for the EarthCache The information for this EarthCache
from the Alaska Geological Survey and the University of Kentucky
Geology Department. I am by no means a geologist.. I use books,
internet, and ask questions about geology just like 99.9 percent of
the geocachers who create these great Earth Caches. I enjoy Earth
Caches and want people to get out and see what I see every time I
go and explore this great place we live in.