When will the Mid-Continent Rift be reactivated and once again cover
northern Minnesota with basaltic lava??
This winter, if all goes according to our model, the weight of the snow
cover will trigger melting by December 17 and, if the stress within the
plate has the proper orientation, an eruption on January 3. Just
kidding.
As I'm sure you are aware, the rift has not been active for about a
billion years and it "failed". It started to split the continent into
two pieces but stopped. I don't think geologists or volcanologists can
predict what will happen to the Mid-Continent Rift in the next hundreds
or thousands of millions of years (although, under certain funding
incentives, I'm sure we could speculate). The rift is important because
it is one of the weakest places in the continent (and the North American
plate). In the future, when the tectonic boundaries change, the stress
in the plate may favor extension. If this happens the rift may be
reactivated. You are correct in that volcanism would probably be
basaltic. Some readers may be thinking that my "arm waving" (an
expression geologists use to refer to unsupported wild speculation) has
reached such grand proportions that I might put out someone's eye. One
example might reign in my speculation (and arms). About a billion years
ago there was a roughly north-south plate boundary near what is now
Utah. As the continent (plate) grew this boundary was abandon. In the
last 20-30 million years, as the tectonic boundary along California
changed, conditions near this old plate boundary changed (from
compression to extension) and volcanism began. Volcanism and earthquakes
have continued in this area since that time. Perhaps you have been to
southern Utah and seen some of the young volcanoes, like
Pavant Butte.
These
volcanoes are along the east edge of the Basin and Range Province, a
broad area of rifting.
Never say never. Northern Minnesota may be once again flooded by
basalt. But don't hold your breath.
Steve Mattox, University of North Dakota
Sources of Information:
LaBerge, G.L., 1994, Geology of the Lake Superior region: Geoscience
Press, Tucson, Arizona, 313 p.
Picha, F., and Gibson, R.I., 1985, Cordilleran hingeline: Late
Precambrian rifted margin of the North America craton and its impact on
the depositional and structural history, Utah and Nevada: Geology, v. 13,
p. 465-468.
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