Delano's Water Treatment Facility

This may help you when reviewing for the Field Trip quiz on May 30/31.

Green River Formation

Students in 8th Grade Earth Science at Delano Middle School were recently working with samples of the Green River Formation from Southwestern Wyoming.  The formation consists of sandstones, mudstones, siltstones, shales and other sedimentary rock types that were deposited in several freshwater lakes.  The Green River Formation is Eocene in age (48 million years old) and has several layers that are very fossiliferous.  Fossil Butte National Monument (http://www.nps.gov/fobu/index.htm) is located within the formation and is well known for the preservation of fish fossils found there.

The sediments of the Green River Formation are deposited in layers, a dark layer representing the summer months and a lighter layer representing deposition in the winter months.  A dark layer and light layer taken together represent one years worth of sediment deposition.  These pairs of layers are called varves, each varve equals one year.  The presence of varves allows students to determine how long the lake was in existence by counting varves, in a way, very similar to counting tree rings.

The varved shale was obtained from the Ulrich's Fossil Fish Gallery and Preparatory (http://www.ulrichsfossilgallery.com/) as approximately 8 inch by 10 inch sheets, about one centimeter in total thickness.

This larger piece of varved shale was then cut down into individual shale billets for student use.

Using various methods of magnification, students were then able to count the number of varves in each shale billet and determine the number of varves per millimeter.  Each block of students came up with a different class average of varves per millimeter, but our averages ranged from 7.3 - 8.1 varves per millimeter.  Stating this another way, it took between 7.3 - 8.1 years to deposit one millimeter of sediment.

Students were then able to calculate how long it would take to deposit a meter's worth of sediment (7,300 - 8,100 years) as well as the entire 260 meter thickness of the Green River Formation (1,898,000 - 2,106,000 years).  Though it may not exactly match the accepted ages for the formation, the numbers obtained by our students are close to the accepted ages.

Plate Boundaries

When preparing for the test coming next week, the fourth outcome on our 'Vocabulary Page' says:
Be able to predict the types of earth surface features that might be present when given the type of plate boundary.  Example - what would you expect to find at the boundary between: a subduction zone, divergent seafloor plates, convergent continental plates and/or transform plate boundary.

The pictures identifies examples of different types of plate boundaries, you should be able to predict what occurs at these boundaries based on the maps you've made in class.
For next weeks test, also plan on being able to identify different plate boundaries (convergent, divergent, transform), i.e. use the picture to help in preparation.

Discovering Plate Boundaries

For the past few class periods, Delano 8th Grade Earth Science students have been working on the activity called 'Discovering Plate Boundaries' developed by Dale Sawyer at Rice University.  This great activity allows students to discover what occurs at tectonic plate boundaries by making observations of real data.  A paper was published in the January 2005 Journal of Geoscience Education describing the activity.

The activity focuses on four different data maps:
1.  Volcanology - this maps shows the locations of currently or historically active volcanoes or volcanic features..

2.  Geography - the map demonstrates the elevation above or depth below sea level in meters.

3.  Geochronolgy - the data on this map indicates teh age of the ocean floor in millions of years.

4.  Seismology - this map shows earthquakes with magnitudes greater than 4 that occurred from 1990 - 1996.  The map also indicates at which depth the earthquakes occurred.

During the activity, students make observations and classify different plate boundaries based on the data provided.  Students first focus on one of the four specialty types described on four data maps, actively placing plate boundaries into different groups due to observations made from the data.  Students are then placed in new plate groups, where each group has a specialist in Volcanology, Geography, Geochronology and Seismology.  This group then classifies the plate boundaries around one specific plate, i.e. the North American plate.

After a short presentation from each group on the different types of plate boundaries surrounding their plate, students are introduced to the three different types of plate boundaries (divergent, convergent, and transform).

    1.  Divergent - areas where plates are moving away from each other.
    2.  Convergent - areas where plates are moving towards each other.
    3.  Transform - areas where plates are sliding past each other.

Different plate boundaries have different characteristics or features that students are now able to identify easily on their maps because they have a knowledge of what is occuring at these plate boundaries.

Thermohaline Circulation

In class this week, we've been looking at the factors that affect ocean currents.  Thermohaline circulation is the name given to large-scale ocean circulation patterns.  It refers to how differences in the densities between warm/cold water and fresh/salt water and how these different densities circulation patterns.

Two types of ocean currents are:
1.  Surface currents - ocean currents that travel at or near the oceans surface.  These tend to be warm water currents.  The Gulf Stream in the North Atlantic is a great example of a surface current.
2.  Deep currents - ocean currents that travel far below the surface of the ocean.  These tend to be cold water currents.

Differences in temperature really drive the ocean circulation.  Warm water is less dense, causing it to rise to the surface.  Cold water is more dense, meaning cold water will sink.  Warm water flows from a low latitude (near the equator, where it's warmed) to a high latitude (the poles, where the water is cooled) as a surface current.  The cold water flows back towards the equator as a deep current.  The picture belows shows warm water sitting on top of cold water because of differences in density.

Salinity, the total measure of dissolved salts or solids in a liquid, also affects density.  Because of the differences in density, less dense fresh water will always sit on top of the more dense saltwater.  The picture belows shows blue fresh water sitting on top of the clear salt water.

Large influxes of freshwater to the oceans can slow or temporarily stop the thermohaline circulation because fresh water will not sink below the more dense saltwater.

In the picture below, knowing that one container holds saltwater and the other fresh water, can you determine which jar holds which type of water?

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.

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's Glacial Story (briefly)

Here's a brief (five minutes or so) narration and/or video diagraming major events in Minnesota's most recent glaciation that students may (or may not) use in preparation for their coming test.

Glacial History of the Rush River County Park

Back on October 28^th, 167 8^th grade students from Delano Middle School visited two sites in the Minnesota River Valley and the Rush River County Park with a long-term goal of discovering the basic geologic history of the area.  At this point of our year, we are most interested in the recent glacial history of the Rush River area.

The Rush River is located entirely within Sibley County, though its watershed includes a portion of two surrounding counties.  The Rush River flows for a distance of 20 miles with an overall change in elevation close to 259 feet.  The calculated gradient of the Rush River is then 12.95 feet per mile.
Within the Rush River valley there are numerous examples of large, rocky point bars that are comprised of nonnative rocks including, basalt, rhyolite, granite, shale, limestone and a few Lake Superior agates.  In many or most cases, these rocks have been deposited hundreds of miles of their original location.  Students on this day spent a large amount of time identifying these different types of rocks and discovering the source areas for these rocks within the region.

The source of the rocks that make up the rocky point bars are found within the river valley.  Glacial till is being continually being eroded from the valley walls.  The picture below shows a prime location of this erosion.  This particular location is comprised of at least three distinct till layers, each with a different source location.  The top two layers contain tills from the late Wisconsin glaciation. 

The uppermost layer has its source in what is called Riding Mountain provenance and is commonly called the Des Moines lobe.  Till or sediment deposits from the Des Moines lobe are at or near the surface for a large portion of the state of Minnesota.  The color of the till is commonly buff or a yellowish brown.  A distinctive characteristic of the till is the presence of a large amount of Cretaceous Shale, the gray Pierre Shale.  Carbonate rocks, like limestone, are also found commonly within this till layer.

The middle till layer seen in the picture above is derived from sediments from the Superior provenance and is commonly called the Superior Lobe.  Till from the Superior lobe is much redder in color and tends to contain more clay material.  Rock types present within the till are indicative of the source area, a large grouping of crystalline rocks including basalt, rhyolite, granite and gabbro and some sedimentary rocks including red sandstone and limestone.  Also found within this layer of till and occasionally on the point bars at the Rush River are Lake Superior Agates.

The lowest layer of till on the picture above (very near the surface of the river) was deposited before the late Wisconsin glaciation and is often referred to as the old, gray till.  This till layer was not used in class and/or referred to often.

Students in our 8^th grade Earth Science classroom have recently been completing lab work on identifying general characteristics (texture and lithological) of four known Minnesota glacial tills (Superior, Wadena, Rainy and Des Moines lobe) from the late Wisconsin glaciation.  When students have identified characteristics of these four known glacial tills, they use this information to identify the source of two unknown glacial tills from the Rush River County Park in Sibley County, Minnesota.  The two unknown tills represent the upper and middle till layers described above or the Des Moines and Superior lobes.

That the Superior lobe advanced on what is now the Rush River County Park first and was followed by the Des Moines lobe is just part of the geologic history of the area.  To complete the story, the relatively high gradient of the river, at least for rivers in the area, needs to be explained thoroughly during a future post on Minnesota’s glacial history.  For a quick (and non-illustrated) version, near the end of the late Wisconsin glaciation, an immense lake called Glacial Lake Agassiz formed from meltwa

ter.  This lake catastrophically discharged forming what is called Glacial River Warren that carved a valley (now occupied by the Minnesota River) across Minnesota several kilometers wide and at least 100 meters deep.  This large valley created ‘knick points’ which resulted in large changes in river/stream channel slopes.  Since the incision of the valley by Glacial River Warren, rivers and streams have been eroding to the base level of the new valley floor in an attempt to level this steep slope.  Since Glacial River Warren carved a valley with steep sides, rivers (including the Rush Rivers) flowing into this valley have higher gradients that also increases their erosional energy.

Some Examples of Weathering

Weathering can be defined as the gradual breakdown of rock materials.  It primarily results from the physical breakdown of rock material (mechanical weathering) or via the chemical breakdown of rock through chemical reactions (chemical weathering).

A nice example of mechanical weathering (especially pertinent for places like Minnesota) is through an action called ice wedging.  As liquid water flows into the cracks of rock materials and freezes during periods of low temperatures, the frozen water expands, widening the crack.  This action can reduce very large boulders to much smaller remants as shown in the pictures below.

These large granite boulders are found just outside Pipestone National Monument near Pipestone, Minnesota.  Granite is not native to the area and would have been deposited there after transport by glaciers.  The boulders are called the 'three maidens', at one point in time there would have been just three boulders of granite, but the repeated freezing and thawing of water have split the boulders into many pieces.  Largely because of how out of the ordinary granite is to the area, a Native American legend grew out of these large pieces of granite.  Native Americans believed that the granite boulders held the spirits of three maidens who required offerings before the quarrying nearby of catlinite (or pipestone) in what is now the National Monument.

Another form of mechanical weathering is abrasion, which is the grinding and wearing away of material through the action of wind or water.  The photographs below show great examples of abrasion at Iona's Beach, a Scientific and Natural Area maintained by the Minnesota Department of Resources along the Lake Superior shore.  On the north end of the beach a large rhyolite flow is found.  Waves break this rhyolite flow down and largely through wave action, these smaller pieces of rhyolite are rounded and smoothed before eventually being deposited on the beach.

Chemical weathering is the breakdown of rock material through a chemical reaction.  This occurs largely through weak acids that are found naturally in our rain or snow and through the oxidation of other materials.  The picture below (taken in Summit Cemetery, Waukesha County, Wisconsin) is a nice example of chemical weathering, over the last 150 years the rock has been exposed to a large portion of natural acids through precipitation.  A closer look at the headstone proves that the original carving into the stone has become much more difficult to read.

Another form of weathering is called differential weathering, which refers to how different rock materials weather (or breakdown chemically or mechanically) at different rates.  The two photographs below show a nice example of differential weathering, the pink feldspar crystals weather more slowly, and as such, seem to stand out from the rest of the granite.

Another very nice example of differential weathering is Devil's Tower National Monument in Wyoming.  The land area around Devil's Tower is comprised of sedimentary rocks, which weather (and then are eroded or transported away) at a much faster rate than the igneous rocks that comprise the monument.  The igneous rocks are much more resistant to weathering than the sedimentary rocks.  Devil's Tower formed as an intrusion of igneous material that, after the surrounding sedimentary rocks weathered and eroded away, was left standing over 1,200 feet above the immediate area.

In our classroom, students recently examined some examples of both mechanical and chemical weathering.  We used different rock types (limestone, rhyolite, basalt, sandstone, marble, gabbro) in our weathering lab.  Students placed these different rock types in weak solutions of carbonic acid to determine the effects of weathering.  The next class period, mechanical weathering through the process of abrasion was explored before comparing both activities.

Working with Stream Tables

These last few weeks our 8th grade students have been working with a stream table designed to simulate and teach basic river principles, including: how river channels form and change over time and how sediment is transported and deposited within river systems.

The stream table was built with an old wood household door that was no longer being used as the base.  It has the dimensions of 1.91 meters long by .85 meters wide.  There are numerous coats of silicon to prevent the leaking of water, these coats are especially thick near joints (after three years of use, there haven't been any leaks yet).  At any given time there is also 25-30 gallons of water being circulated throughout the system by a submersible pond pump.

The modeling media inside the stream table is manufactered thermoset plastic from Composition Materials Company (http://www.compomat.com/) in Milford, CT.  It is sold by them as 'Stream Table Mix' and consists of various sizes and densities that do an exceptional job of modeling on sediment is transported and deposited in natural river systems.  We use anywhere between 50-80 pounds of plastic within the stream table for student use.

The idea of using a large stream table came from seeing an example created by the folks at Little River Research & Design (http://www.emriver.com/). 

Minnesota Continental Divide Student Map

The state of Minnesota has four major continental divides which are shown on all Minnesota roadmap.  Because of these divides, Minnesota shares it's water with a large part of the North American continent as water flows downhill, based largely on water flowing away from these divides.

Students recently were required to map the location of these divides and other surface water features found within the watershed.  Some of the surface waters students needed to include on their map include major lakes (Mille Lacs, Upper/Lower Red, Winni, Superior, etc) and major rivers (Mississippi, Minnesota, St. Croix, Red, etc.).  An example of a student completed map is posted for reference.

Minnesota's Continental Divides

Water is one of Minnesota's most important natural resources.  Continental divides force water to that falls on one side of them to flow one direction, while water that falls on the other side flows the other direction due to gravity.  The majority of water that falls on Minnesota drains through a series of rivers to the Mississippi River and ultimately, the Gulf of Mexico.

In the southwestern portion of the state, another high area or divide, forces water that falls in that area to drain to the southwest towards the Missouri River.  Of course, the Missouri River ultimately flows into the Mississippi River and then the Gulf of Mexico.  Of course, this particular picture was taken in Minnesota, though it's a continuation of the same divide.  This picture was taken near Carroll, Iowa.

Across the northern portion of the state runs the Laurentian Divide.  Water the falls to the north of this divide flows to the north towards Hudson Bay, in Canada's far north.  Water falling to south of the Laurentian Divide flows either to the Mississippi River or towards Lake Superior.  Water that flows to Lake Superior ultimately flows through the Great Lakes to the Atlantic Ocean.

In places where two continental divides meet you can find triple divide points or triple points.  On of these three way continental divides occurs in Minnesota near Hibbing.  The exact triple divide point is located inside the private property of a taconite mine, so it is not accessible to the public.  Early Native Americans living in the area called this spot "the hill of three waters."

Looking at the picture below (source:  http://commons.wikimedia.org/wiki/File%3ANorthAmerica-WaterDivides.png) you can find several other triple divide points.  One of interest would be the one located at Triple Divide Peak in Glacier National Park.  Water falling on this location flows three directions; west to the Pacific Ocean, north to the Arctic Ocean, and east to the Atlantic Ocean.  This is apparently the only location on the planet where water flows into three separate oceans.

Most might find the pictures of continental divides as rather boring, especially when you compare the Minnesota pictures to the picture of the continental divide located at Loveland Pass in Colorado.  Loveland Pass is located on the Great Divide, this divide separates water that flows in the Pacific Ocean from that that flows in the Atlantic Ocean.  The Great Divide runs across a series of mountain ranges from North America all the way to the Andes in South America.

Our 8th grade students have been using Minnesota roadmaps this week to map out locations of continental divides located in our state.  Using this information, they then map major rivers and lakes and determine how waters flow throughout our state.

Help with Calculating the Mississippi River's Gradient

Take a look at the attached files and use these as a guide or homework check for you assignment that is due soon.

The gradient of a river measures the change in elevation over a certain distance.  All rivers flow downhill due to the force of gravity.  To calculate gradient, you must find the change in elevation between two locations and divide that by the change in distance.
Since we measure elevation in feet and distance in miles, the units for gradient will be feet per mile (ft/mile).