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.

Minnesota Geology Monday - Minneopa Falls

Minneopa Falls is a highlight of the Minneopa State Park run by the Minnesota Department of Natural Resources (http://www.dnr.state.mn.us/state_parks/minneopa/index.html).

Minneopa is a Dakota word meaning 'water falling twice' representing the two falls within the state park.  Minneopa State Park is a short drive from Mankato (for a little bit of United States history, Mankato is the site of the largest mass execution in the U.S., but that's for another story).
The falls formed when Minneopa creek flows over the Cambrian-aged Jordan Sandstone.  Because of differential cementation of the sandstone, areas with more cement form the top level of the double waterfall.

The upper falls is small, falling six or seven feet.  Once over these first falls, Minneopa creek flows approximately seventy feet before reaching the lower falls.

At the lower falls, the creek falls 40 feet.  This particular waterfall on the creek is the second highest waterfall in southern Minnesota.  The highest waterfall in the region is only slightly higher and is also found nearby.

Minneopa Falls was formed when Glacial Lake Agassiz discharged catastrophically via Glacial River Warren.  Glacial River Warren carved a large valley (250 feet deep and up to 5 miles wide in places) that created various knickpoints that caused rivers or creeks to adjust their gradients to reach this new baselevel.  Glacial River Warren created this new knickpoint at Minneopa Creek approximately 9,700 years before present and during that time, the falls have migrated upstream almost 0.75 miles.

Beneath the lower falls, if the waterlevel in the creek is low enough, you are able to walk quite near falls themselves and examine large sandstone blocks that have fallen from overhead.

Minnesota Geology Monday - Iona's Beach

Iona's Beach is located 43 miles Northeast of Duluth and just 3 miles north of Gooseberry Falls State Park, along the shore of Lake Superior.  The Minnesota Department of Natural Resources has designated area as a Scientific and Natural Area (http://www.dnr.state.mn.us/snas/sna01000/index.html).  Iona's Beach is near the former site of the Twin Ports Resort and is named after the former owner of the resort, Iona Lind.  Located adjacent to Minnesota State Highway 61, the rock beach is approximately 300 yards long, as seen in this Google Earth image.

The beach is comprised of flattened pink rhyolite pebbles, also known as shingles.  The source area of the rhyolite pebbles is a cliff on the northern edge of the beach.  As Lake Superior's waves erode the rhyolite cliff, individual rhyolite shingles are rounded and tranported along the beach.  A basalt outcrop portrudes into Lake Superior on the beach's southern edge.  This basalt outcrop prevents rhyolite pebbles from moving beyond the area and effectively traps the pebbles in this location.

At the northern edge of the beach, the rhyolite cliff is located.  The rhyolite lava flow is associated with the 1,100 million year old Midcontinent Rift System as are most of the rocks of this area of the state.  The cliff is 20-30 feet above the lake level.

The area closest to the rhyolite cliff is comprised of fairly angular pebbles, since these materials have not been transported very far and as such, the amount of time they have been weathered is limited.

Looking south from the rhyolite cliff, you can see the basaltic point that extends into Lake Superior, effectively trapping the rhyolite pebbles.

Closer to the southern edge of the beach, the rhyolite pebbles are much more rounded and smooth, due to the weathering that has occurred as they have traveled from the source area with the assistance of longshore drift in the lake.

Minnesota Geology Monday - Jeffers Petroglyphs

In southwestern Minnesota, between the communities of Jeffers and Comfrey, is a Minnesota Historical Site called the Jeffers Petroglyphs (http://www.mnhs.org/places/sites/jp/).  The earliest carvings at the Jeffers Petroglyphs were done approximately 7,000 years ago by early Native Americans and some carvings extended until recent times.

From the interpretive center, it is a short trail walk to the petroglyphs site.  The rock outcrop that the glyphs have been carved into is no more than a few football fields in size.

Prominent bedrock in southwestern Minnesota is comprised of Archean gneisses and 1,700 million year old Sioux Quartzite.  The petroglyphs have been carved into the Sioux Quartzite.  Throughout the area, the quartzite ranges in color from pink to purple, at this location is is largely pink.  The quartzite is derived from quartz sand.  The source location of the quartz sand grains is the Penokean Mountains, which were located across central Minnesota and into Wisconsin during Proterozoic times.  As these mountain ranges were weathered and eroded, most minerals would have been changed into clay and easily transported away.  The weathering resistant quartz, were transported south and deposited largely by rivers.

Cross-beds and ripples found in the quartzite indicate the direction of movement of the flowing water as the quartz sand grains were being deposited.  The majority of cross-beds and ripples suggest a southward direction.  There are a few locations known of southward-dipping cross-beds found directly beneath northward-dipping cross-beds.  This suggests that the depositional environment would have been near an ocean shore under the influence of tides.

The carvings would have been done by using another rock type of equal or greater hardness than the Sioux Quartzite.  Carvings include birds, turtles, bison, thunderbirds, weapons and a great number of other objects.  The site most likely represents a religious illustration of important aspects of the lives for these earlier Native Americans.

Also found throughout the site are numerous glacial striations in the quartzite, representing evidence of past glaciation during the Late-Wisconsin glaciation.  The glyphs are carved over the striations, ensuring that they are younger than the glacial period before them.

The Jeffers Petroglyphs site is found in the area of the state that once was large prairies before European settlement.  The site is home native prairie grasses and wildflowers and is also one of the few areas in the state where you can find prickly pear cactus growing.