June 7, 2019– Mary Greeley News – According to the Minnesota Department of Transportation, a portion of the highway near Granite Falls has closed after a fault line began to separate.
Minnesota contains some of the oldest rocks on Earth, granitic gneisses that formed some 3,600 mya (million years ago) — roughly 80% the age of the planet. About 2,700 mya, the first volcanic rocks that would later underlie Minnesota began to rise up out of an ancient ocean, forming the Superior craton. This craton later assembled into the Canadian shield, which became part of the North American craton.
MnDOT reports the crack separated one inch per day.
A detour has been posted for the closed portion of the highway.
The road collapse is located between County Road B1 and 600th Street near the Upper Sioux Agency State Park entrance. The road has been closed since March.
Below is a photo of Hwy 67 taken on April 5, 2019:
Below is a photo of Hwy 67 taken on May 24, 2019:
According to MnDOT this closure and detour is expected until Fall 2019.
“The prevailing idea is that the movement of the North American plate away from the mid-Atlantic ridge toward the subduction zones on the Pacific Coast set up a subtle, but pervasive stress in the interior of the continent,” Chandler said. “That stress might be sufficient to jostle old faults that formed many millions or billions of years ago in Minnesota’s case, that remain, even though the tectonic forces that built those faults are long since quiet.”
Area of Fault Movement
The supposed biggest quake recorded in Minnesota history happened in Long Prairie in the 1860s. Its magnitude was an estimated 5. Estimated, because seismographs weren’t used to measure a significant Minnesota earthquake until later.
Several other earthquakes in the state’s history have been big enough to get people’s attention.
Minnesota earthquakes, 1860–2018
Name Year Magnitude
Long Prairie 1860-61 5
New Prague 1860 4.7
St. Vincent 1880 3.6
New Ulm 1881 3.0-4.0
Red Lake 1917 3.8
Staples 1917 4.3
Bow String 1928 3.8
Detroit Lakes 1939 3-3.9
Alexandria 1950 3.6
Pipestone 1964 3.4
Morris 1975 4.6-4.8
Milaca 1979 1
Evergreen 1979 3.1
Rush City 1979 0.1
Nisswa 1979 1
Cottage Grove 1981 3.6
Walker 1982 2
Dumont 1993 4.1
Granite Falls 1994 3.1
Brandon 2011 3.12
Source: Minnesota Geological Survey
350m years ago this was an area of volcanic eruption with lava flows and mafic dikes.
The continental craton reveals a history of episodes during which it and its margins behaved as a single rigid block without significant difference in behavior between shelf areas and areas of previous or later basinal tendency. Such episodes are marked by the sequence-bounding unconformities which extend as unbroken surfaces across the axes of earlier basins.
Additional episodes of widespread stability are indicated by sedimentary units which exhibit uniform low rates of thickness and facies change in apparent disregard of previously established tectonic patterns. In contrast to these times of craton wide stability there are other episodes with records which clearly indicate a marked tectonic differentiation of the craton into epeirogenic uplifts, shelves, and interior basins. The most obvious criteria are the increased thicknesses deposited per unit time, and the marked facies response to basin subsidence (basin-center evaporites, euxinic shales, barrier-reef trends and other hingeline phenomena).
credit: In part with https://www.minnpost.com/environment/2018/12/yes-there-are-earthquakes-in-the-land-of-10000-lakes/