michigan’s sand dunes ?· mi deq gsd - michigan’s sand dunes - pa 07.pdf page 4 of 12 from...

Download MICHIGAN’S SAND DUNES ?· MI DEQ GSD - Michigan’s Sand Dunes - PA 07.PDF page 4 of 12 from clay…

Post on 29-Jun-2018

212 views

Category:

Documents

0 download

Embed Size (px)

TRANSCRIPT

  • MICHIGANS SAND DUNES

    Geological Survey DivisionPamplet 7

    By Steven E. Wilson Lansing, Michigan

    Copyright 2001 by the Michigan Department of Environmental Quality (DEQ) Geological Survey Division (GSD).The DEQ GSD grants permission to publish or reproduce this document, all or in part, for non-profit purposes.The contents of this electronic document (whole or in part) can be used if, and only if, additional fees are notassociated with the use or distribution of this document and credit is given to the DEQ GSD and the author(s).This copyright statement must appear in any and all electronic or print documents using this file or any partthereof.

  • MI DEQ GSD - Michigans Sand Dunes - PA 07.PDF page 2 of 12

    Geological Survey DivisionPamplet 7

    AN MICHIGANS STUDY OF COASTALSAND DUNE MINING IN MICHIGAN

    By Steven E. WilsonLansing, Michigan, 1979, 2000

    Copyright 2001 by the Michigan Department of EnvironmentalQuality (DEQ) Geological Survey Division (GSD). The DEQ GSDgrants permission to publish or reproduce this document, all or inpart, for non-profit purposes. The contents of this electronicdocument (whole or in part) can be used if, and only if, additionalfees are not associated with the use or distribution of thisdocument and credit is given to the DEQ GSD and the author(s).This copyright statement must appear in any and all electronicor print documents using this file or any part thereof.

    Table of Contents

    INTRODUCTION....................................................... 2WHAT IS SAND?...................................................... 2WHAT ARE SAND DUNES?.................................... 2HOW ARE SAND DUNES FORMED? ..................... 2WHERE DO WE FIND SAND DUNES? ................... 4WHY ARE SAND DUNES FOUND IN

    MICHIGAN? ................................................. 6DUNE CYCLES......................................................... 7USES OF DUNE SAND ............................................ 8DUNE ENVIRONMENT............................................. 9SELECTED BIBLIOGRAPHY................................. 11OTHER THINGS TO LOOK FOR AT THE DUNES 12

    INTRODUCTIONMore and more, "natural resource" is becoming ahousehold word. Increasingly, we have become awareof the importance of our natural resources and some ofthe problems relating to wise resource development,management and use. A major point to remember isthat some resources are non-renewable. That is, theycannot be replaced, replanted or regrown. InMichigan, one non-renewable resource is commonlyoverlooked - or even taken for granted. The resourceis sand. In particular, sand dune sand. Sand dunesare a natural wonder with beauty and majesty all theirown. However, when you know more about the dunes,they take on even greater significance. Once you learnabout the complex, dynamic dune ecosystem, you willappreciate dunes even more. Because of the highdemand for Michigan dune sand and its unique

    character it is the subject of many in-depth technicalreports. This pamphlet is designed to introduceMichigan's Sand Dunes to you.

    WHAT IS SAND? Before we try to describe a sand dune, we need toknow what sand is. This question does not have asimple answer. The designation "sand" does not referto how the material was formed or what it is made of.Sand can, and does, come from all three major rocktypes: igneous, metamorphic, and sedimentary. Sandcan be primarily one mineral or material, or it can be amixture. However, in the most general sense sand isconsidered any loose, granular material having grainswhich are sand sized. Technically, sand is restricted toparticles ranging from 0.0625 to 2.0 millimeters indiameter. That is a vast range of sizes. Many peoplehave tried to define sand more precisely. It should bekept in mind that characteristics of sand may varygreatly within a deposit.

    Additional confusion arises because the term sand isused to describe a deposit or area, regardless ofparticle size. To a geologist the term would beimproperly used if 50 percent or more of the grains arenot sand size. In summary, it should be pointed outthat there are more than 100 terms which apply tosand and sandstone (the major rock formed fromsand).

    WHAT ARE SAND DUNES?Sand dunes are mounds of windblown sand which varygreatly in size, from less than one meter to tens ofmeters high. The size depends upon the supply ofsand. There is even greater variation in the areacovered by dunes. In Michigan, the smallestdimension is usually the distance from the shoreinland. Many of the more recognizable dune forms areridges or complexes of mounds or crescents. Theshape of individual dunes is equally variable. Shaperelates to the direction and strength of the wind formingit, as well as to the amount of sand available.

    HOW ARE SAND DUNES FORMED?Sand dunes can and do form in many areas. However,some requirements must be met. Required elementsare: I) a source of dry sand, 2) a means to sort andtransport the sand, and 3) a land area on which todeposit the sand. Recent studies indicate that a supplyof dry sand is the most important factor. The means oftransporting and sorting are not rare or out of theordinary. Running water and normal winds can do this.Strong winds or water action cannot initiate duneformation without a supply of sand. As mentioned, thesize and shape of a dune depend on the wind and

  • MI DEQ GSD - Michigans Sand Dunes - PA 07.PDF page 3 of 12

    amount of sand available. The amount of sand beingequal, wind conditions have a strong influence on theshape of a dune field. Constant winds tend to formmore regularly shaped dunes or even long ridges.Irregular or changing wind directions result in irregular-shaped dunes.

    The sand making up Michigan's dunes is almost allone mineral - quartz. However, there are duneselsewhere in the world which are made primarily ofother minerals, such as calcite or gypsum. Becausesand dunes are wind-laid deposits, they are formed inlayers (stratified). Furthermore, the general shape of a

    Idealized parabolic dune

    Dune platform

    Overriding dunes

    En echelon and overlapping dunes

    Domal dunes

    Association of various dune forms

    dune results in two different sets of beds. There is agently sloping windward set of beds and a moresteeply sloping downwind set. At times, the dunesmove or migrate. This movement results in cross-bedding of the sand layers. The cross-bedding foundin sand dunes helps geologists to distinguish dunedeposits from other landforms.

    Because quartz grains can form from a number ofdifferent rocks, the original source of the quartz dunesand cannot be singled out. It should be noted thatrelatively few bedrock outcrops occur in Michigan.Instead, glacial drift almost completely covers theState. Therefore, one can safely assume that sand forthe dunes comes from the drift. Yet, much of the sandfound in drift is mixed with a variety of other particles,

  • MI DEQ GSD - Michigans Sand Dunes - PA 07.PDF page 4 of 12

    from clay to cobble size. The drift is eroded,transported, sorted and redeposited by water - therunning water of a river or the pounding surf of abeach. Water tends to concentrate sand-sizedparticles in particular areas.

    Continued erosion and transportation of sandreplenishes the sand blown into the dune. As long asmore sand is supplied, the dunes will continue to grow.When the supply diminishes, the dunes are likely tostabilize, or at least stop growing. Places where sandaccumulates are numerous in near-shoreenvironments. You may have noticed this along manyof the lovely beaches. Sand, if available, accumulateson the beach as well as out into the lake to a varyingdegree.

    The size range of sand grains that make up dunes isremarkably close. This is because grains that aresmaller-than-sand-size (silt or clays) are carried fartheraway by the action of wind and water. Grains orstones that are larger-than-sand-size (pebbles,cobbles, boulders, and the like) are left behind. Whenenough of the larger materials (usually small toconfused with tubes formed around the roots of plantsgrowing on the dunes. An easy test will distinguish afulgerite from a root cast. Place the specimen in acontainer of vinegar. If it fizzes and falls apart, it was aroot cast. The cementing material was dissolved bythe slightly acid vinegar. However, if the specimen is afulgerite, it will not be affected to any great extent bythe vinegar bath.

    medium size stones, 10 mm or more) are left behind, arock pavement or lag gravel is formed. This caneffectively stop further erosion of sand. The larger,immobile stones cover the sand, preventing furthermovement.The dunes leave their inprint on the thingsaround them. One common artifact of the sand dunesis a windkanter or ventifact. Much of the sand movedby wind bounces along very close to the surface. Thisbouncing movement is called saltation or traction.Sand moving in this manner is very abrasive. Thewind carrying its load sandblasts the stones. Thisresults in the development of flattened to slightlyrounded, highly polished faces on the stones. One ormore faces can develop on a single ventifact. Studiesof the orientation of ventif act surfaces help to indicatethe prevailing wind directions in a dune field.

    Also found in sand dunes are fulgerites. These aretubes of fused sand, formed when lightning hits thesand. The tremendous heat and energy releasedwhen lightning strikes the sand welds the grainstogether. (Temperature exceeds l,7000C.) Fulgeritesare rather fragile and hard to find. They are easily confused with tubes formed around the roots of plants growing on the dunes. An easy test will distinguish a fulgerite from a root cast. Place the specimen in a container of vinegar. If it fizzes and falls apart, it was a root cast

Recommended

View more >