Dunes An Alex Boukamp

Presentation

Michigan's Coastal Dunes

Formations

History

Threats

The coastal dunes along shores of Lake Michigan are among the most striking natural features in the state of Michigan

Lake Michigan dunes come in a variety of shapes and sizes

The Formation of Michigan's Coastal Dunes

Lake Michigan dunes are relatively young in geological terms

As long as 16,000 years ago Michigan was covered by thousands of feet of glacial ice

It contained a mix of boulders, cobbles, sand, and clay

During glacial melting these materials were left behind and are known as glacial drift

Formation Cont…

This glacial drift is what composes most of the sand in lake Michigan coastal dunes

The sands were either eroded from glacial drift along the coast by wave activity or eroded from inland deposits and carried by rivers and streams

Only the hardest, smallest, and least soluble sand grains were moved

Waves and currents eventually moved these tiny rocks inland, creating beaches along the Great Lakes shoreline

Formation Cont…

Winds from 8 to 24 mph began moving the sand grains The size of sand is directly related to the wind speed,

larger grains and clumps require higher wind speed These bouncing sand grains resemble tiny, skipping ping

pong balls as they are moved by the wind through a process called saltation

The sand will eventually meet an obstruction such as some grass causing it to clump on the ground and slowly make a small mound

Formation Cont…

Now we have a dune that is beginning to form though it is a rather slow process

Its continued growth depends on perennial vegetation, wind, and sand

Because dune plants act as barriers to sand movement and hold migrating sand, they play a critical role in the formation and stabilization of dunes

Formation Cont…

The wind continues to push sand grains up the windward side of the dune crest, causing the dune to grow in the downwind direction

Many sand grains continue moving and eventually roll down the steep back slope

Straight Forward Diagram

A profile view of a typical dune sequence in P.J. Hoffmaster State Park shows relative sizes and locations of the following dune types:

Fordune Dune Ridge Blowout Parabolic Dune Backdune

Foredunes

Low very active dunes

Parallel to the beachNamed for there

position, the are the first dune inland from the beach hence the name FOREDUNE

Dune Ridge

The dune ridge is located between the foredune if one is present and the parabolic dune

The dune ridge is taller than the foredune

Blowouts

Blowouts are depressions made by wind erosion in already existing sand deposits

Blowouts occur on any dune

Parabolic dunes are large blowouts

In this photo the blowout used to be bare but the blowout shaped it into a parabolic dune

Parabolic Dunes

Sometimes referred to as coastal blowouts

Crescent shaped with tips pointing up wind

Blowouts in their centers

Parabolic Dunes Cont…

They nest into one another away from the beach

The oldest parabolic dunes are found furthest inland

Fordunes become parabolic and migrate inland

Backdunes

Refers to stabilized dunes separated from the shoreline by other dunes giving them protection from wind erosion

Because of the lack of wind erosion forests begin to develop and soils form

Backdunes Cont…

Not a distinct type of dune based on shape or method of formation

They are merely stabilized parabolic dunes, foredunes, and dune ridges

There forest covering shows that they have been inactive for many years

Ripples

Among the smallest landforms created by wind

Much in common with dunes but the sizes don’t overlap

Ripples form when wind moves over dry, bare, sandy surfaces

Ripples Cont…

Most Ripples are roughly aligned at right angles with the wind that formed them

If you are observant you will be able to tell which direction the wind is traveling at by the angle of the the Ripple

Dark Layers

The sand of Michigan coastal dunes is mostly quartz

other minerals such as feldspar, magnetite, hornblende, garnet and calcite are also present

magnetite and other dark minerals like hornblende sometimes collects in dark patches or layers on the beach and dune surfaces

Dark Layers Cont…

Dark Layers form on beaches the waves causes the minerals to accumulate

Dark Layers occur on dunes when wind and gravity move the sand around

Many people believe at first glance that Dark Layers are in fact pollution but that is a boldfaced lie

Sand Pillars

Sand Pillars form when there is uneven moisture in a beach or dune surface and the wind erodes the drier sand, leaving the wetter sand behind

The moister in the sand holds the grains together and makes the Pillars more resistant to wind

Eventually the Pillars dry out and erode away

Sand Pillars Cont…

One activity that may cause uneven moisture in a beach or dune surface is water draining into the sand unevenly after a heavy precipitation event

The preferred pathways for water drainage become the wettest, and these pathways turn into the pillars when wind removes the drier surrounding sand

Wind Circles Wind Circles are the

traces left behind when the wind moves the leaves of a plant and the leaves brush the sand surface, the outcome is often pretty neat looking

Half circles are most common when the wind has a dominant direction

Full circles can indicate more variation in wind direction

Mining

Once sand dunes are gone they are gone for goodMining is not just a threat it is the most

destructive and irreversible damage being done to dunes

Houses generally don’t cause entirely to much damage to dunes, in fact dunes can heal themselves from that but once it is mined it can never be brought back

Mining Cont…

Not only do we loose these unique and rare dunes but we also loose the flora and fauna that call them home

Even the companies that do mine admit how severe the damage to the dunes are

The reason there is more mining in the southern are is because up north they are not actually dunes

Mining and Sand Dune Diagrams

Mining Cont…

Foundries have used sand to produce metal casting for centuries

It is used to make a cast and metal is poured into the cast and BINGO you have your product

Mining Cont…

Over 50 million tons of sand have been mined since the late 70’s

There are 6 things foundries look for in good sand– Grain Shape– Bonding Ability– Refractoriness– Durability– Chemical Composition

Dune Plant Life

Beach Grass or Marram Grass– Beach Grass is extremely

important to the survival of a sand dune

– It holds the sand in place with its roots

– It is capable of growing quickly to change with shifting sands

– You should avoid walking on beach grass so as not to damage it

Plant Life Cont…

Side Oats or Grama Grass– Is essential to dune

stability

– A threatened species

Perched Dunes

Perched Dunes exist on a surface that is above the level of lake Michigan

The wind travels up the bluff and picks up sand along the way and drops it on the top

This can completely remove clay from the area

The parts with dune grass are actual dunes but the slope going down is a glacial deposit

Perched Dunes Cont…

Sleeping Bear Dunes is a good example of perched dunes

The dunes lie on top of glacial moraines which rise 30 to 360 feet above lake Michigan

The Legend of Sleeping Bear Dunes

Long ago, in the land that is today Wisconsin, Mother Bear and her two cubs were driven into Lake Michigan by

a raging forest fire. The cubs swam strongly but the distance and the water proved too much for them. They

fell further and further behind and ultimately slipped beneath the waves. When Mother Bear reached the

Michigan shore, she climbed to the top of a bluff and peered back across the water, searching vainly for her

cubs. The Great Spirit saw her and took pity on her plight. He raised North and South Manitou Islands to mark the place where her cubs vanished and laid a slumber upon

Mother Bear.-Ojibway Indian Legend