Minnesota Geology Monday - High Falls of the Pigeon River

The Pigeon River flows along the United States and Canadian border and is home to the highest waterfall in the state of Minnesota.  The High Falls of the Pigeon River is a waterfall of approximately 120 feet in height.  The Pigeon Rivers source is very near the Laurentian Divide, the area of high ground that separates water from flowing to Hudson Bay to water flowing to Lake Superior.  

Downstream from the waterfall, the Pigeon River has cut a fairly deep gorge through the Rove Formation.  The Rove Formation is an 1,850 million year old sedimentary formation consisting of layers of shale, sandstone and siltstone deposited in an ancient sea.

The sediments in the Rove Formation were deposited horizontally in the Animikie Basin.  The source of the Rove sediments are Archean rocks found to the north.  

Above the Rove Formation are the 1,110 to 1,105 million year old Logan intrusions, a large mafic intrusion that consists of numerous vertical dikes and horizontal sills in the area.  At the High Falls, the Rove Formation is capped by a diabase sill that is resistant to erosion.  Since the diabase is resistant to erosion, Pigeon River flows over the diabase and erodes the much softer sedimentary rocks of the Rove Formation.

Downstream of the waterfall are many diabase boulders that have been eroded out of the sill and transported downstream.

The High Falls are easily accessible via trails from the visitor center and rest area at the Grand Portage State Park (http://www.dnr.state.mn.us/state_parks/grand_portage/index.html).  The trail to the falls is approximately 1/2 mile in length and is paved.  The last length of trail is a raised wooden walkway.  There are several overlooks at the end of the trail giving visitors different vantage points to the waterfall.

Minnesota Geology Monday - Mount Rushmore

Minnesota Geology Monday will move the borders to South Dakota in the spirit of President's Day.  Mount Rushmore National Memorial is managed by the National Park Service (http://www.nps.gov/moru/index.htm) and brings almost two million people to the area anually.  This Google Earth image shows the immediate area around Mount Rushmore in the Black Hills.

Construction of the monument began in 1927 and ended in 1941.  Original plans called for the presidents to be sculpted from the waist up, but due to lack of funding, the sculpture was limited to their heads.  Each head is roughly 60 feet tall.  George Washington, Thomas Jefferson, Abraham Lincoln and Theodore Roosevelt were chosen for their roles in the United States during the first 150 years of the nation’s existence.

Gutzon Borglum selected Mount Rushmore for several reasons.  First, the granite weathers slowly, allowing sculpting.  Second, Mount Rushmore is the tallest mountain in the area (5,725 above sea level).  And lastly, the mountain faces southeast, which would allow the workers to be in the sunlight most of the day.

Mount Rushmore is composed of granite of the 1.6 - 1.8 billion year old Harney Peak granite batholith.  Pegmatite dikes are also found throughout the region and can be seen as streaks in the Lincoln and Washington heads.

The Harney Peak batholith intruded into earlier mica schists.  During the Paleozoic Era, sedimentary rocks were deposited onto the granites during the Cambrian.  The Black Hills was uplifted 70 million years ago during the late Cretaceous, during the Mesozoic Era.  This uplift allowed erosion to remove the softer sedimentary rocks and exposing the granite.

Originally, the Jefferson sculpture was going to be placed on Washington's right, but the granite turned out to be inappropriate for sculpting.  The work that had been done in the area was later smoothed by dynamite blasts.

Beneath the sculpture, the talus pile remains from construction of the monument.

Minnesota Geology Monday - Barn Bluff

In Red Wing, alongside the Mississippi River, people have the opportunity to explore Barn Bluff.  Historically, the bluff has served the purpose of being a visual reference for explorers along the river.  Today, visitors can hike a several mile trail to the top of the bluff (the steepest areas have stairs) for some very interesting views of the Mississippi River and the city of Red Wing, but be careful, as recently as the fall of 2011 a woman fell to her death.

The Google Earth images give a sense of Barn Bluff's location in respect to Red Wing and the Mississippi River.  Barn Bluff stands approximately 350 feet above the valley floor.  Barn Bluff was formed as Glacial Rvier Warren carved the Minnesota River valley the Upper Mississippi River valley's.  During this point, Barn Bluff would have stood out as an island within the much larger river.

Barn Bluff is comprised of nearly horizontal laying strata deposited in an ancient ocean during the Paleozoic Era.  The uppermost layer or top bluff is the Oneota Dolomite of the Prairie Du Chen Group.

Below the Oneota Dolomite are several layers of Cambrian sandstones, including the Jordan Sandstone and glauconitic sandstone of the Franconia Formation which has now been included in the Tunnel City Formation.  This sandstone takes it's green color from the mineral glaconite, which is a green clay mineral.

Near the intersection of US 61 and MN 58 is a normal fault called the Red Wing Fault.  Here the uppermost Cambrian Formation, the Jordan sandstone, has dropped 125 feet to lie adjacent to the glauconitic sandstone of the Franconia Formation.

A well marked parking lot near the southern end of Barn Bluff is the starting point for hiking to the top of the bluff.  The Oneota Dolomite is also frequented by rock climbers in the area.

Along several points of the trail, especially on the eastern (or river side), there is a very steep drop to the bottom of the bluff.  Though there are numerous great overlooks along the trail as well allowing you to view the Mississippi River.

When you have finally reached the north end of the bluff, the views looking over Red Wing and the river valley make the hike well worth the time and effort.

Constellation Review

For the upcoming test, students may choose to review the eight required constellations using this brief video.  Of course, the method to review these constellations it to spend some time viewing and observing them outside.

Minnesota Geology Monday - Magnetic Rock

Near the end of the Gunflint Trail, in northeastern Minnesota is a hiking trail that leads to Magnetic Rock.  The trail is approximately one mile in length and mostly uphill (at least on the hike in).  In the picture below, you can make out a small portion of the Gunflint Trail near the trailhead, the picture was taken about 1/4 mile into the hike.

Due to a forest fire in 2007, there are relatively few mature trees or vegetation along the trail.  This fire also did an excellent job of exposing bedrock outcrops throughout the area.  When looking north at several points along the trail, you see numerous exposures of the white, granitic Saganaga Tonalite.

The majority of the trail is on top of the 1,878 million year old Gunflint Iron Formation, which would have been deposited near the shoreline of an ancient sea.  The Gunflint Iron Formation consists of black to gray chert alternating with black iron-rich layers.  A goal this summer is to also acquire better photographs of the Gunflint Iron Formation, in particular the bedding planes, which is largely horizontal in the area.

Along the trail to Magnetic Rock, you are also able to view stromatolites within the Gunflint Iron Formation.  Though the day I traveled to the area a storm was coming in and I needed to complete the hike and set up camp, so I didn't have time to look for the stromatolites.  Maybe that can happen this summer.

Magnetic Rock is a large piece of the iron formation that has been turned vertical, probably by the southwestern trending Rainy lobe during the late Wisconsin glaciation.  Magnetic Rock is almost 25 feet from ground level to the top.  Due to it's height, the rock is visible for some distance along the trail before you actually reach it.

The bedding planes of the Gunflint Iron Formation is largely horizontal in the near vicinity of Magnetic Rock.  The bedding plane of Magnetic Rock is vertical, indicating that it has been moved from it's initial location.

Astronomy Software or Apps

Like what's been said in class, the next five or six weeks will be spent covering a variety of topics on astronomy.  For the first few weeks we'll be focusing on constellations and the moon.  Students will need to be able to identify by sight or picture eight constellations (Canis Major, Canis Minor, Orion, Gemini, Taurus, Ursa Major, Ursa Minor, and Cassiopeia)  that are easily visible in the night sky during February.

Here are some free downloads that may be helpful for you during this month:

 

Computer (Mac or Windows):

Stellarium – the planetarium program that was used during class for our introduction to the eight constellations we need to know.  It's a free download that I've used on both Apple and Windows systems, with no problem.
http://www.stellarium.org/

Android apps:

All of these are free and use many of them.

Solar Dynamics – cool Sun stuff
Sundroid – Moon/Sun rise/set times
NASA – tons of stuff
Moon Phases – moon stuff
Google Sky Map – star charts/constellations
SkEye – another star chart/constellations
S&T Sky Week – short descriptions of daily astronomical happenings
APOD – Astronomy Picture of the Day
Where is Io? –  finds the positions of Jupiter’s four largest moons

 

iPad/iPhone/Touch apps:

Phases - moon stuff
SkyView - star charts/constellations
Star Atlas - star charts/constellations
Moon Globe - moon stuff
Mars Globe - Mars stuff
Planet Finder - planets
MoonMapPro - moon stuff
APOD – Astronomy Picture of the Day
Starquake - cool sun stuff
NASA - tons of space stuff 
Star Walk - star charts/constellations 
Solar Walk - planets/solar system 

Note:  The items in bold/italics are the apps that I tend to use on a somewhat regular basis.