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Sleeping Bear Dunes

National Lakeshore

Michigan

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Sleeping Bear Dunes National Lakeshore, Michigan

The lakeshore is covered by recent (Holocene) alluvium and dune sand and Pleistocene glacial deposits (Handy and Stark 1984). Unconsolidated material, mostly sand, is the recent alluvium that forms present-day, riverine floodplains. The deposits of greatest areal extent occur along the Platte River. Two levels of sand dunes occur in the lakeshore – dunes near the current level of Lake Michigan and others on morainal plateaus 300 feet above the lake.

Glacial deposits, primarily moraines and outwash areas, in the lakeshore range from 500 to 700 feet thick (Handy and Stark 1984). Lakebeds formed after glacial retreat and during the post-glacial variations in the Lake Michigan water level. The deposits closest to the land surface and the physiography, in general are the result of glacial advance and retreat during the last glacial period, the Wisconsin. The study of the underlying bedrock has been infrequent because of the thickness of the glacial deposits.

Consolidated rock or bedrock underlies the glacial deposits. This bedrock consists of layered sedimentary units, primarily sandstone, shale and limestone (Handy and Stark 1984). Antrim Shale of Mississippian age and limestone of the Traverse Group of Devonian age underlie the bedrock. That bedrock that has been eroded is at altitudes ranging from below sea level to 200 feet.

Wallbom and Larson (1998) updated the surficial geology of the national lakeshore. They further delineated the recent and glacial deposits of Handy and Stark (1984) by recognizing 15 deposits.

The geologic history between the deposition of the Traverse-Antrim formations and the glacial deposits is unknown (Handy and Stark 1984). Apparently, either rocks were not deposited or any deposition was eroded during this time period.

Soils

There are eight soil associations in the national lakeshore (National Park Service 1979; National Resources Conservation Service 1996). All of the soil associations are characterized by low available water capacity, primarily because these soils are well drained. The Kalkaska/Mancelona and Kiva/Mancelona associations are found on the glacial outwash plains. The soil of the beach ridges and lake terraces is the East Lake/Eastport/Lupton association. On wooded and active dunes the soil association is Deer Park/Dune. The remaining soil associations – Emmet/Omena, Emmet/Leelanau, Kalkaska/East Lake, and Leelanau/Mancelona – are all associated with moraines and to a lesser extent glacial till plains. As one might expect, these morainic soils are found on steeper slopes than the other soil associations.

Glacial and Post-Glacial History of the Sleeping Bear Dunes Area

Overview:
The physical geography of Michigan and the Great Lakes is largely the result of the sculpturing, erosion, and deposition of materials by the advance and retreat of glaciers over the last 2 million years – the Pleistocene Epoch. These glaciers scoured the surface of the earth, leveled hills, and altered the previous ecosystem. Valleys created by the river systems of the previous era were deepened and enlarged to form the basins of the Great Lakes. Millennia later, the climate warmed causing retreat of the glaciers as they melted. Glacial retreat was followed by a relatively static interglacial period during which vegetation and wildlife returned. The cycle was repeated several times. The most important glacial advance for northwestern Michigan is the Wisconsin stage, which retreated from Michigan about 9,500 to 15,000 years ago.

As the glaciers retreated, meltwater formed along the front of the ice. Because the land was greatly depressed at this time from the weight of the glacier, large post-glacial lakes formed. These lakes were much larger than the present Great Lakes. Their legacy can still be seen in the form of beach ridges, eroded bluffs, and flat plains located hundreds of feet above present lake levels. Also, the land began to rise as the glaciers retreated. This uplift (or crustal rebound) and the shifting ice fronts caused dramatic changes in the depth, size and drainage patterns of the post-glacial lakes. Although this uplift has slowed considerably, it is still occurring in the northern portion of the Lake Michigan basin.

The land-sculpting effect of continental glaciation in northwest Michigan is clearly illustrated in the geologic features of the Sleeping Bear Dunes region (National Park Service 1961; Drexler 1974). The evidence indicates that Wisconsin ice lasted from approximately 50,000 to 10,000 years before present, with the ice having disappeared from the Sleeping Bear region about 11,800 years ago. During and following glacial retreat, the water levels of the Great Lakes fluctuated as they sought the lowest outlets, with the final adjustment as we know them today taking place about 3,000 years ago (Drexler 1974).

Immense headlands, characteristic of the Lake Michigan shoreline in the vicinity of Sleeping Bear Dunes, for the most part, resisted the force of the advancing ice and steered the ice lobes into the valleys. The ice lobes gouged debris from the valley floors and deposited it along the sides of the valleys when the ice finally melted, creating prominent moraines. Generally, these moraines and the valleys between them are oriented in a north-south direction. The formation of the Manistee moraine (Figure 3) is considered to be the climatic event of glacial processes that shaped the Sleeping Bear Dunes area (National Park Service 1961).

Meltwaters flowed southward from the glacier front and formed extensive outwash plains in southern Leelanau County and northern Benzie County. Where meltwater cut through the Manistee moraine, a drainage channel leading southward into the Platte River plain area was formed. The meltwater in several channels flowed opposite to the direction in which the streams run today; when the ice blockage disappeared, the flow was reversed and the streams began to run into the Lake Michigan basin.

As the glacial ice receded to the north, an immense volume of meltwater filled the Lake Michigan basin to form post-glacial lakes at four successive levels—Lakes Algonquin, Chippewa, Nippissing and Algoma. The elevation and extent of these lakes were dependent on the elevation of the lowest outlet available during that period. Drexler (1974) constructed figures of these successive lake stages of deglaciation in the national lakeshore. Evidence of these lakes can be seen through features such as wave-cut bluffs, beach terraces, sand bars, ridge and swale formations, and old sandy lake plains. When water receded from the lake plains, many smaller lakes were left in the embayment areas. In addition to mixed glacial materials, tremendous amounts of sand accumulated at various points throughout the region. These were later shaped by wind into the unusual variety of dunes found between Point Betsie and Good Harbor Bay, which include ancient dunes associated with the post-glacial lakes and modern dunes.

As the Wisconsin ice retreated out of the Lake Michigan and Lake Huron basins, the southern outlets of these glacial lakes were abandoned in favor of lower northern outlets (Drexler 1974). Ultimately, the water level in the Lake Michigan basin fell to an elevation of about 230 feet. This low-level lake is called Lake Chippewa. The low-water stage began about 10,000 years ago, and culminated in Lake Chippewa at about 7,500 years ago. Lake Chippewa gave way to the rising water level of the Lake Nipissing stage about 5,000 years ago when southern outlets again became functional because of continual crustal rebound in the north.

The Nipissing Lake stage ended about 3,500 years ago. From this time until 3,000 years ago the water level in the Lake Michigan basin lowered slowly in response to the continued downcutting at the northern outlet. A pause in the lowering occurred when the water level reached 595 feet – called Lake Algoma (Drexler 1974). Within the park there is little evidence for a distinct Algoma stage. Over the last 80 years the water level in the Lake Michigan basin has remained rather constant, ranging from 571 to 575 feet (http://www.huron.lre.usace.army.mil/levels/hleumh.html).

Formation of Hydrological Features at Sleeping Bear Dunes National Lakeshore Seven substages of the Wisconsin stage are recognized (Hough 1958). These substages occurred successively to the north, the last being north of the Great Lakes. The fifth or Port Huron substage is the most important in the Sleeping Bear region, though the sixth or Valders substage briefly touched the area.

A highly developed morainic system from south of Manistee northward around the tip of the Lower Peninsula characterizes the Port Huron substage. This system includes a series of end moraines, ground moraines, outwash areas, glacial channels, deltas and glacial lakebeds. During the early part of the Port Huron substage most of the lower peninsula was ice-free; by the close of the substage the Lower Peninsula was completely ice-free. Therefore the characteristic topography of the Sleeping Bear region was fashioned during this time.

The northwestern corner of the Lower Peninsula is indented by a series of lakes, lowlands and bays. These features set this region apart from the area to the south. One reason for the prominence of this area is pre-glacial landscape. Though the evidence of the pre-glacial landscape is lacking, it is generally accepted that existing topography influenced the direction of ice movement (Flint 1957). In addition, following lines of least resistance, glacial ice advancing south along pre-glacial channels and along larger topographic features of the Great Lakes should be expected to show a highly lobate nature.

As the main ice lobe of the Port Huron substage advanced southward in the Lake Michigan basin, lateral lobes pushed glacial debris into the lowland valleys of tributaries. Between these tributary lobes a series of ‘interlobate’ moraines formed. In time these tributary lobes merged and pushed to the Port Huron maximum. In the tributary valleys the ice was thicker with more power to shape the landscape. After the thinner upland ice melted, the valley ice lobes remained, thus greatly influencing the glacial topography of the area.

As retreating ice melted, lakes formed between the ice margin and the end moraines. Water levels of these lakes rose until they cut outlets through the moraines forming outwash plains and glacial channels along the morainal front. These newly formed drainage systems were independent of the pre-glacial system. Flow in these channels depended on glacial volume and the extent of glacial melting; glacial topography largely controlled flow direction. Channels flowed between moraines formed by the Port Huron substage and those of previous substages. As the ice retreated northward, however, lower elevations were exposed and many streams abandoned the old glacial channels for these lower areas.

The final advance of the Port Huron substage formed the Manistee Moraine. During the formation of the Manistee Moraine, the ice edge maintained a nearly static position where melting equaled advance. The previous drainage pattern had been obliterated by previous glacial advance, though outwash channels formed a new drainage system, much of which is still extant today. Along the ice margin a vast river of meltwater was flowing south.

Meltwater eventually cut through three channels in the Manistee moraine; the most important was the Glen Lake Channel. This channel undercut the other ice border drainages and became the outlet for the area west of Grand Traverse Bay for a long while. A river of meltwater meandered southward from Glen Lake; skirted the ice filled Empire Embayment; flowed over the outwash plain east of Otter Lake and around the inner margin of the ice of the Platte Lobe; found its way into the ice filled Crystal Lake depression; flowed west of Benzonia and south along what is now the northward flowing Betsie River; and joined the shallow upper end of the Manistee ice border lake.

The Port Huron substage ended, when the ice re-treated farther northward and these ice border channels were vacated. Later, Valders ice flowed far to the south in the Michigan basin but the landscape/drainage systems were not visibly altered.

Following the retreat of the Valders ice, northwestern Michigan was never glaciated again. However, though the inland topography had been decided by Port Huron Ice, the shoreline underwent changes during the evolution of the glacial and post-glacial Great Lakes.

At the beginning of the Lake Algonquin stage (water elevation of 605 feet – 25 feet above present lake level), the lakeshore would have consisted of long peninsulas (interlobate moraines and islands intersperse with deep, narrow bays). At the end of this stage, the shoreline evolved to the point of truncating the moraines and sealing off at least part of the bays with bars and beaches.

The Lake Nipissing stage is also at an elevation of 605 feet. Because some crustal rebound occurred in the area of the lakeshore between the two stages, the shore features of the two lake stages are separate -- Nipissing shore features lie lower than those of the Algonquin stage.

For the national lakeshore, Calver’s (1946) work in the Platte and Crystal lake depressions is the only detailed work on post-glacial shorelines. The Platte Lake Embayment forms an 8x8x6-mile triangle (Figure 4), almost equally divided by the small Platte interlobate moraine. It contains nine lakes with two separate drainages. Originally, the Platte Embayment was a Lake Algonquin bay with the Platte Moraine forming islands.

Following crustal rebound, the Platte Moraine probably formed two bays during the Nipissing stage. The Nipissing shoreline impounded a large lake including Long, Rush, Platte and Little Platte lakes and possibly the Otter Creek lakes.

Under the wave-cut bluffs east and north of the Otter Creek lakes are a series of cold flowing springs. These springs flow southwesterly towards Otter Creek, which flows north-northwest. In this area an extinct lake once existed, the bed of which is heavily underlain with marl deposits.

The springs, the primary source of Otter Creek’s flow, apparently come from ground water flow in the old Glen Lake glacial drainage from about the midpoint of the Empire Meander southward. It is possible that Otter Creek once drained into the Platte Embayment, but filling of the embayment during the Lake Nipissing stage blocked this flow. Later drainage to the north may have been responsible for the extinction of the former lake.

The Bar Lake Embayment, about 3 miles long and 1.5 miles wide, is bordered to the northeast by the Sleeping Bear Moraine and to the south by the Algonquin shoreline. The Algonquin shoreline appears as a series of beach ridges that pass directly through the town of Empire to their connection with the Empire Bluffs. Behind the shoreline lay a concentric lagoon, still discernable as a low depression.

During Nipissing times both the Empire and Sleeping Bear Moraines projected farther lakeward than at present. A shoreline was built spanning the embayment and creating a crescent-shaped lagoon. North and South Bar lakes were created by a series of large, barrier-beach dunes that dissected the lagoon.

The most visible shoreline feature at Glen Lake is the wave-cut north face of the Glen Lake Moraine, a prominent beach ridge along the north side of Glen Lake. Little Glen Lake once opened northwesterly to Lake Michigan between the Sleeping Bear and Glen Lake Moraines; however, this channel has long been filled by the sands of the Sleeping Bear Dunes.

At Good Harbor Bay, Bass, School and Lime lakes, all at an elevation of 620 feet, were closed off early during the Lake Algonquin stage. During the Lake Nipissing stage, a crescent-shaped belt of dunes closed off Little Traverse Lake. The Lake Algoma stage or the present shoreline, however, probably closed off Shell Lake.

Source National Park Water Resouces Division http://www.nature.nps.gov/water/completedwrmp.htm

References

Calver, J. 1946. The glacial and post-glacial history of the Platte and Crystal lake depressions, Benzie County, MI. Michigan Geological Survey, Pub. No. 45, pt. II.

Drexler, C. 1974. Geologic report on Sleeping Bear Dunes National Lakeshore. In Natural History Report for Sleeping Bear Dunes National Lakeshore by U. of Michigan . Sleeping Bear Dunes National Lakeshore, Empire, MI.

Flint , R. 1957. Glacial and Pleistocene geology. John Wiley and Sons, Inc., New York , NY .

Handy, A. and J. Stark. 1984. Water Resources of Sleeping Bear Dunes National Lakeshore, Michigan . U.S. Geological Survey, Water-Resources Investigations Report 83-4253, Lansing , MI .

Hough, J. 1958. Geology of the Great Lakes . Univ. of Illinois Press, Urbana .

National Park Service. 1961. A proposed Sleeping Bear National Lakeshore, natural history report. National Park Service, Washington , D.C.

National Park Service. 1979. Resource information base, Sleeping Bear Dunes National Lakeshore. National Park Service, Denver Service Center, Denver, CO.

National Resources Conservation Service. 1996. Final report for soil digitatization of Sleeping Bear Dunes National Lakeshore. On file at Sleeping Bear Dunes National Lakeshore, Empire, MI.

Wallbom, T. ;and G. Larson. 1998. Surficial geology of the Glen Haven, Glen Arbor, Good Harbor Bay , Empire, Burdickville, and Beulah 7.5 minute quads, Leelanau and Benzie counties, Michigan . Michigan State University , Lansing , MI .

Brief Description of Park Geology

On the northwestern shore of Michigan’s lower peninsula lies Sleeping Bear Dunes National Lakeshore, a hilly region fringed with massive coastal sand dunes and dotted with clear lakes. It is a diverse landscape, embracing quiet, birch-lined streams, dense beech-maple forests, and rugged bluffs towering as high as 460 feet above Lake Michigan. Several miles offshore, surrounded by the unpredictable waters of Lake Michigan, sit the Manitou Islands, tranquil and secluded.

Aerial view of Sleeping Bear Dunes.
Aerial view of Sleeping Bear Dunes.

A Masterpiece of Ice, Wind, and Water

Indians were the first to tell tales of how sand dunes and other features of the land were created. In more recent years scientists have sought to explain the complex geologic history of the area. An abundance of clues has helped. Fossils tell of some of the earliest history, when shallow warm seas covered this area. More recent history is revealed in the landscape. The shoreline, the hills and valleys, the many small lakes, and the sand dunes you see today are evidence that the powerful earth-moving forces of ice, wind, and water have been at work here.

Often, geological changes occur slowly over millions of years, but here you can witness dramatic changes within your lifetime. Twice in this century landslides at Sleeping Bear Point sent large land masses plunging into Lake Michigan. In a matter of years, trees disappear as shifting dunes bury them under a blanket of sand. Such changes make Sleeping Bear Dunes an exciting place to visit and revisit.

During the Ice Age continental glaciers spread southward from Canada, repeatedly burying this area under sheets of ice. These massive glaciers enlarged river valleys, carving out the wide, deep basins of the Great Lakes. They deposited huge piles of sand and rock debris when they melted, leaving behind the hilly terrain you see today. Finally, 11,800 years ago, the last glacier retreated.

With the glacial landscape formed, Lake Michigan and many smaller lakes began taking shape. The level of water filling Lake Michigan's ice-carved basin rose and fell many times before reaching its present level. The lake's shoreline-at first irregular with jutting headlands and recessed bays-was gradually smoothed out. Waves wore back the headlands. Shoreline currents carrying sediments built sandbars and spits across bay mouths. Sometimes sediments dammed bays, creating small inland lakes such as Glen Lake near the Lake Michigan shoreline.

Lake Michigan shoreline at Sleeping Bear Dunes National Lakeshore.
The glaciers left behind an ideal setting for building sand dunes: a sandy coast on the leeward side of Lake Michigan. Prevailing westerly winds blowing across the lake build two kinds of dunes in Sleeping Bear Dunes.
  1. Beach dunes develop on low-lying shores of Lake Michigan. Their main ingredient is beach sand. The Aral Dunes, along Platte Bay's north shore, are good examples of beach dunes.

  2. Perched dunes, on the other hand, sit high above the shore on plateaus. Glacial sands atop these surfaces supplied material for these dunes. The Sleeping Bear Dune of Indian legend is a perched dune.

Some dunes migrate, pushed by the wind. Sometimes shifting sands bury trees. Then, as the dunes move on, "ghost forests" of dead trees are exposed, stark reminders of the dunes' passing. Not even man has escaped the influence of windblown sand. U.S. Coast Guard buildings now located in Glen Haven had to be moved from Sleeping Bear Point in 1931 because migrating dunes threatened to cover them.

Beachgrass and sand cherry are among the first plants to grow on newly built dunes. They play an important role in dune development. They help build dunes by acting as obstacles that slow sand-laden wind and force it to drop its load. Their roots hold sand in place and stabilize dunes. But if a strong wind succeeds in stripping plants from a dune, a bowl-shaped blowout can be excavated in the exposed area. Vehicles are prohibited on the dunes because they destroy dune vegetation. Tire track scars last many years.

Sand dunes are stabilized by Beachgrass roots.
Sand dunes are stabilized by Beachgrass roots.
Detailed Park Geology

Sleeping Bear Dunes National Lakeshore
Park Geological Setting
By Scott Lundstrom

Bedrock

Bedrock subcrop that underlies the area of Sleeping Bear Dunes National Lakeshore (SLBE) is shown on Milstein (1987) as the Devonian Traverse Group with a fringe of overlying Antrim Shale along the southeastern margin of the area. The strata dip gently southeastward into the Michigan Basin (a Paleozoic bedrock structural basin centered on the southern peninsula of Michigan, and not to be confused with the Lake Michigan basin). The fossiliferous limestones of the Traverse Group includes reef limestones with Hexagonaria coral, of which the famous Petoskey stones of this region are composed. However, Petoskey stones and a great variety of other Paleozoic and Precambrian rock types that make up the gravel in the much younger Quaternary deposits of the region were rounded and polished during transport by glaciers, rivers, and by wave action on beaches, as described below. The bedrock is generally buried at SLBE by as much as 600 feet of Quaternary deposits.

Quaternary Deposits

The Quaternary stratigraphy which dominates the landforms and thick surficial materials of SLBE, consists of Pleistocene glacial deposits of a continental ice sheet, and postglacial Holocene materials deposited by a variety of surficial processes associated with lakeshores, wind, rivers, and hillslopes. Glacial forms constitute the largest elements and main relief of the landscape. The associated glacial deposits compose the bulk of the materials underlying the landscape, but were then modified and reworked by lakes, streams and wind in postglacial time. Earth’s climate history of the past 1 million years or so is dominated by a cyclicity of many glaciations separated by interglaciations like the one in which we presently live and have developed our modern civilization. However, the glaciated landscape of the SLBE region was developed mainly near the end of the last glacial advance onto the lower Peninsula of Michigan during latest Pleistocene time.

Late Pleistocene Glaciation

Thick Quaternary deposits dominate the visible geology of Sleeping Bear Dunes National Lakeshore.
Thick Quaternary deposits dominate the visible geology of Sleeping Bear Dunes National Lakeshore.

We infer from dated buried peats that at least some of lower Michigan was ice free about 35,000 years ago, but by about 24,000 years ago at the last glacial maximum, the Laurentide ice sheet, which covered most of Canada, had extended south across all of Michigan to a latitude of about 40 degrees N across central Indiana, Illinois, and Ohio. At this time, the SLBE area, as in the rest of Michigan, was under several thousand feet of ice and the glacial deposits probably consisted of little more than a thin discontinuous basal till over bedrock at the base of the glacier. Most glacial deposits and landforms were deposited near the glacial margin. North of the last glacial maximum margin, there are numerous moraines marking stillstands and minor readvances in the general northward retreat of the ice margin. Even by about 14,000 years ago, the entire area of present lake Michigan and most of Michigan were still occupied by an active glacier that formed probably coeval elements of the Valparaiso and Lake Border moraines (Lundstrom et al, 2001). However, by about 12,000 to 13,000 years ago, all of the lake and lower peninsula of Michigan were ice free as shown by the dated buried forest at Two Creeks Wisconsin and by the Cheboygan bryophyte bed near the Mackinaw Straits. As far as I know, Twocreekan peat or other organic deposits have not been found and dated in the SLBE area. It is likely that this area was vegetated then, and remnant organic materials should have been buried by deposits of the next glacial advance, if they were not totally destroyed by it. If such glacially buried organic materials are known or discovered at SLBE, they would be of great scientific value (and I would like to be notified).


Greatlakean Advance

The latest glacial advance onto the southern peninsula of Michigan occurred after the Twocreekan interstade as shown by glacial till which overlies the Cheboygan bryophyte bed and the forest bed at Two Creeks. The time of this last glacial advance is called the Greatlakean substage. A band of uplands and ice contact features known as the Manistee moraine extends north near the lakeshore from Manistee into this area and was correlated to the Greatlakean substage by Evenson (1973). This glacial advance is not well understood as indicated by its scanty and contradictory coverage in the existing literature. The prevailing paradigm (Farrand and others, 1984, Wallbom and Larson, 1999) is that Greatlakean ice only extended as glacial fingers into embayments into the pre-existing glacial headland but left no prominent end moraines. These embayments are now occupied by Glen Lake, Empire, and Platte Lake, as well as by Lake Lelanau and the arms of Grand Traverse Bay. In this paradigm, the deposits that form the pre-existing glacial headland were formed prior to the last advance.

The latest glacial advance and its deglaciation is interpreted herein to be associated with the major suite of glacial landforms and deposits of the area. There are two types of terrain associated with the advance – terrain formed in front of the glacier (proglacial), and that formed beneath it (subglacial). The most extensive landform type in the region, though only a small part of SLBE park area, is the proglacial pitted outwash plain. It includes most of the area traversed by highway M-72 between Traverse City and Empire, and occurs within the park in two areas: one is in the SLBE outlier (that includes Bow Lake) southeast of Burdickville; and the other is the area just north of the park boundary within the north halves of sections 15 and 16 and northeastern section 17 in Empire Township. The outwash deposit is composed of stratified and sorted sand and gravel that represents an aggradational deposit of a large discharge of meltwater and sediment at and beyond the ice sheet margin at that time. The surface of the deposit forms a plain that slopes gently southward from just above 300 m (about 1000’) altitude where it contacted the ice margin south of Glen Lake (within the above-mentioned areas) to the proglacial lake Chicago level to which it grades near Manistee. The plain is 20-40 km wide and formed between the ice margin about 10 km inland of the present Lake Michigan shore and the upland to the east which was formed at an earlier ice margin. This plain is interrupted by numerous closed depressions called kettles, of which some but not all contain lakes. The depressions were formed when blocks of ice were buried by sand and gravel outwash, then the ice melted and formed a void after sand and gravel deposition ceased. The Park outlier that includes Bow Lake is oriented over an elongate N-S trending set of closed depressions, and illustrates the typically complex collapsed kettle topography formed by ice blocks buried in outwash. The uncollapsed high rim of the outwash plain surface forms the rim of this kettled area within this park outlier. The north and west margins of the outwash plain approximate the glacial margin and occur within the park as north- and west-facing scarps in sections 15, 16, and 17 in Empire Twp.

Though the area of the outwash plain within the park is relatively small, the outwash deposit has a greater significance to the hydrology and ecology of the area and park resources through its influence on the quality and quantity of linked ground water and surface water resources. Because this upland deposit is composed of permeable sand and gravel, the outwash plain is a main ground-water recharge area and the deposits comprise a principal aquifer of the area. This aquifer discharges to lower wetlands and lakes in the kettles such as in the outlier that includes Bow Lake; to river and stream systems that dissect this aquifer, such as the Platte River with its lower end in the park; and to other wetlands within SLBE north and west of the scarp margins at the head of outwash. Water quality is greatly affected by these relations, and will be discussed in a later section.

Subglacial features form both uplands and lowlands within SLBE to the north and west of the head-of-outwash glacial margin. The glacial deposits that form the uplands south of Empire and southwest, north, and east of Glen Lake are composed largely of stratified sand and gravel similar to that of the above pitted outwash plain, but have a much different surface form. They do not have pitted or planar form. Instead, their ridged form is indicative of subglacial molding by basal sliding and associated subglacial hydraulic systems. There are prominent linear subparallel southeast-trending ridges on these uplands that are good examples of ice molded (drumlinized) topography. Though they are not classical drumlins found elsewhere, they indicate subglacial molding and glacial flow direction, which is generally southeastward in this area. Good examples occur south of Empire and in the area traversed by the Pierce Stocking Drive. Since these forms occur on deposits composed of stratified sand and gravel like outwash, the simplest explanation is that they were first deposited as proglacial outwash which was overridden during the latest advance. This explanation contrasts with that offered by Wallbom and Larson (1999) who interpret at least some of these ridges as crevasse fills. The geometry of clay and silt beds, as well as paleochannels within the stratified sand and gravel strata of which these uplands are composed are significant to the groundwater hydrology, pore pressures, and their relation to landsliding of coastal bluffs on these uplands (Jaffe and others, 1998, 2000).

A separate aspect of the form of these uplands is their relation to adjoining lowlands. Especially prominent in the area northeast of Glen Lake, the ridges are bounded, subdivided, and intermingled with a set of anastamozing valleys. This valley system does not have the form and characteristics of subaerial streams, but was probably eroded into the glacially overridden sand and gravel by a vigorous subglacial hydraulic system. This subglacial hydraulic system supplied the proglacial outwash system discussed above with abundant meltwater and sediment. These subglacially formed tunnel valleys range in width from less than 100 m to several km, such as that now occupied by Glen Lake. These onshore lowland valleys appear to be continuations of large-scale offshore valleys known from bathymetry (Holcombe and others, 1996). However, coastal and eolian processes and sedimentation have significantly modified and infilled these subglacially formed valleys along and near the lakeshore, as discussed below.

Both the pitted outwash plain and subglacial features described above relate to the latest glacial advance and its termination in this area, but there are also some noteworthy deglacial features in SLBE. As the subglacial hydraulic system waned and the glacier front receded, it no longer supplied discharge to the outwash plain. Some deposition of similar sediment occurred to form inset (kame) terraces between the glacier and the newly formed scarp at the head of outwash. These terraces occur in the park in sections 9,10, 11 and 14 of Empire Township. Block slumping, shore erosion, and fluvial processes may also have contributed to the formation of these terraces and north-facing scarps. A large glaciofluvial system was then superimposed on these kame terraces as evidenced by incised fluvial meanders that occur just east of Empire – they are depicted as a glacial drainage channel on the geologic map figure of NPS, 1998. This channel could only have developed in this position by being confined between the head of outwash and stagnant glacial ice that occupied the lowlands that now contain Empire, Glen Lake, and Platte Lake. Moreover, the incised nature of the channel indicates a sediment-poor meltwater system from the stagnant ice sheet, in marked contrast to the earlier sediment-rich outwash system. Similar features occur elsewhere near Lake Michigan (Lundstrom and others, 2001), but the incised meander near Empire is remarkable.

The stagnant ice sheet in the northern Lake Michigan basin probably disintegrated and retreated rapidly northward as a calving front developed along a lake at its margin. The large proglacial lake developed into glacial Lake Algonquin, which was the cause of many high erosional shoreline scarps in northern Michigan. It may be the erosional source for some of the high scarps found in and near SLBE north and west of the head of outwash. The west facing scarps that appear to be superimposed on the banks of the above-described erosional channel in sections 17, 19, and 20 of Empire township might be Algonquin shore features or they may only be fluvial scarps cut during the evolution and incision of the paleochannel.

Postglacial (Holocene) Processes and Record: Lake level history and shoreline processes

There have been three major controls on the level of lake Michigan in postglacial time: changing outlets, isostatic rebound, and climate. Glacial recession uncovered lowlands on the east side of Lake Huron at North Bay, Ontario while the crust was still isostatically depressed from the weight of the ice sheet and had not yet rebounded. This caused the upper Great lakes levels to be lowered about 8000 to 9000 years ago to levels much below that of Lake Algonquin – Lake Michigan was lowered to a level about 90 m below present (Lake Chippewa). This caused river systems to incise in response to the lower base levels, as interpreted by Barnhardt and others in offshore stratigraphy north of Glen Lake. As isostatic rebound raised the North Bay outlet, lake levels also rose, and the lakes eventually discharged through southern outlets. This transgression to levels several meters above present is termed the Nipissing transgression, upon which has been superimposed smaller events like influxes of water from Lake Agassiz (Colman and others, 1992). Climate has been the main control on short term variability in lake level in the past 5000 years, with a more steady superposed effect of isostatic rebound that exponentially decreases with time and distance southward (Larsen, 1987).

Shore processes respond to climatically determined lake levels. At high lake levels, storm waves erode and undermine bluffs composed of readily eroded unconsolidated glacial deposits, which in this area are largely composed of sand and gravel. Continued landward erosion at the base of bluffs would increase the angle of slope, but slope processes tend to maintain characteristic angles of about 35-42 degrees on these slopes (Nash, 1980), as long as the slopes continue to be actively undermined by waves. Wave swash and longshore currents transport eroded material both along and offshore (Jaffe and others, 1993) to areas of lower energy , which tend to be the embayments that are relicts of subglacial processes described above. Initial spit growth closed off bays to become lakes such as Platte, Glen, Bass and Little Traverse Lakes. Continued but episodic lakeward accretion of sand into these embayments formed concentric rows of beach ridges during high lake levels (Baedke and Thompson, Thompson and others, 1997) with intervening swales representing lower levels between the highstands that formed each beach ridge. The authors interpret their data to indicate highstand and beach ridge cycles of about 30 and 150 years, and that most beach ridges formed between about 1000 and 2500 years ago.
Dunes: eolian forms, process, and history

Sand dunes accumulate and evolve where there are permissive combinations of sand supply and wind conditions. At SLBE, dunes are generally associated with present or past coastlines, but dune form, distribution, activity, stratigraphy, and history exhibit great variety within the park. Dune form ranges from common parabolic forms (also commonly open to the southwest) to longitudinal, transverse, and foredune ridges, and hybrid forms that defy categorization. Dunes occur in the lowland embayments along Platte Bay, Sleeping Bear Bay, Good Harbor Bay, and Empire, and in perched positions on glacial uplands of Empire Bluffs, Sleeping Bear Plateau, and Pyramid Point. The Manitou Islands also exhibit their own unique combinations of all of the above categories. The active dune field of the Sleeping Bear Plateau grades northward into the lowland at the west end of Glen Lake. The upland dunes include intradunal areas with exposed glacial gravel. Ventifacts occur where gravel is exposed to sandblasting action. Nonvegetated active dunes, including blowouts, are interspersed with sparsely vegetated plant communities that coexist with some level of dune activity, and contrast with dense, mature hardwood forest on inactive dunes. Buried soils exposed by dune activity and coastal erosion indicate that stability and instability of the eolian landscape vary during recent time.

Loope and Arbogast (2000) applied radiocarbon dating to many paleosols (past soils) that represent forest soils that were buried by dune activity in the SLBE area. The dates span much of the past 5000 years with more than half the dates being less than 1500 years. Moreover, the authors state that a majority of the sand volume of sites in the SLBE area was emplaced above buried soils dated at 1500 calendar year before present or younger. They favor a model in which dune building , whether in perched or lowland positions, occurs at high lake levels and interpret their dates from the length of the eastern shore of Lake Michigan to indicate an approximate 150-year cycle in dune building synchronous with the lake level record of Thompson and others (1997). Increased sediment supply is plausible during shoreline bluff erosion, especially of the large sandy bluffs like that of the SLBE uplands, but so is a greater sediment supply from greater extent of exposed beaches during low lake levels and transitions to them, as we see this year. The relation of dune activity to lake level is complicated because both are related to climate. As hinted at by charcoal being one of the types of dated material, fire history related to climate and human history is also a likely variable in dune history.
Coastal Hillslope Processes: landslides, scarp evolution

Geomorphic processes on hillslopes include landsliding and smaller scale processes like creep, rain splash, and tree throw. Catastrophic landsliding of coastal bluffs at Sleeping Bear Point has occurred in 1995, 1971, and 1914 (Jaffe and others, 1998, Barnhardt), and should be considered an intermittently active process and potential hazard. The 1995 landslide moved approximately 1 million cubic meters of material that included an approximately 500 m section of coast, with slide materials extending to 3-4 km offshore. Barnhardt and others relate the unusually high frequency of landslides restricted to this section of the coast to a paleochannel and unconfomities in the Quaternary stratigraphy that they investigated in the subsurface and beneath the lake by geophysical methods. They further relate the stratigraphy and unconformities to the postglacial lake level history discussed above, though other scenarios to create the unconformities are also possible.

Though smaller-scale, less catastrophic processes such as creep and treethrow are difficult to observe, they are significant and probably more generally applicable to hillslope evolution of paleo-shorelines, and to other scarps and hillslopes produced during the dynamic history discussed above. Nash (1980) investigated the evolution of shoreline scarps of Nipissing, Algonquin, and modern age elsewhere in northwest Michigan and found consistent systematic differences in form, such as maximum scarp angle and curvature that can be explained by a steady-state model, and which could be used to identify age groups of shorelines at SLBE.

Fluvial processes

Though glaciofluvial processes were of major importance in the glacial deposits and landforms described above, the only modern river in SLBE is the lowest few kilometers of the Platte River between Platte Lake and Lake Michigan. Its course here has a remarkable coincidence with the inflection in the curvature of parallel beach ridges that occur on either side of it, suggesting a relationship between fluvial sediment transport, the location of Platte River point over time, and beach ridge formation.

Another notable feature and process that occurs in this part of the river is tufa precipitation, which will be discussed in the next section.

Hydrology and Water Quality

A good overview of the water resources and hydrology of SLBE is provided by Handy and Stark (1984), but I would like to note a potentially important phenomena that may not be previously described or investigated. In reconnaissance, I observed very young, probably active calcitic (CaCO3) tufa precipitation in the Platte River near the M22 Bridge. Since coatings of this tufa a few mm thick occur on rocks recently used to stabilize the bank and on the shells of living snails in the river, the tufa must have formed in the past few years. The origin of the tufa is unknown, but probably merits further investigation and monitoring because Ca is considered a limiting nutrient to ecosystems and may be an important aspect of the park ecology and resources. A microbiologic origin would not be surprising but precipitation also probably requires supersaturation with respect to CaCO3. The groundwater and surface water resources have relatively high Ca and HCO3 (Handy and Stark, 1984). It is likely this is related to the abundance of limestone clasts and permeable nature of the glacial deposits, especially the outwash plain that is dissected by most of the length of the Platte River and its tributaries. Groundwater may be acquiring its high values of Ca and HCO3 by dissolution of limestone clasts in the sand and gravel aquifer. Groundwater discharge is known to be the dominant component of flow of northern Michigan rivers, and that probably is the case for the Platte River. Since snowmelt is a major source of groundwater recharge, groundwater temperatures are cold and coldwater rivers such as the Platte River warm on their way downstream in summer months especially with residence time in shallow lakes like Platte Lake. Calcite is less soluble at warmer temperatures so tufa precipitation is favored in the warmer waters of the lower Platte River in the summer.

References
Baedke, S.J., and Thompson, T.A., 1993, Preliminary report of late Holocene lake-level variation in northern Lake Michigan: Part 1: Indiana Geological Survey Open-file Report 93-4.

Barnhardt, W. A., Jaffe, B. E., Kayen, R. E., 1999, Mitigation of landslide hazards at Sleeping Bear Dunes National Lakeshore, Michigan, (abs.) Geological Society of Abstracts with Programs.

Barnhardt, W. A., Jaffe, B. E., Kayen, R. E., 1999, Evaluation of landslide hazards with ground-penetrating radar, Lake Michigan coast: Coastal Sediments '99, v.2, p. 1153-1165.

Barnhardt, W.A., Jaffe, B.E., Kayen, R.E., and Cochrane, G.R., 2001, Lake-level change and coastal landslides at Sleeping Bear Dunes National Lakeshore, Lake Michigan, USA: Journal of Coastal Research (submitted, in review).

Calver, J.L., 1946, The glacial and post-glacial history of the Platte and Crystal Lake depressions, Benzie County, Michigan: Part II of Occasional Papers on the Geology of Michigan, State of Michigan Department of Conservation, Geological Survey Division Publication #45, Geological Series #, p. 1-70.

Colman, S.M., and 8 others, 1994, Lake-level history of Lake Michigan for the past 12,000 years: the record from deep lacustrine sediments: Journal of Great Lakes Research, v. 20, p. 73-92.

Dorr, J.A., and Eschman, D.F., 1970, Geology of Michigan, University of Michigan Press.

Dow, K.W., 1937, The origin of perched dunes on the Manistee Moraine: Papers of the Michigan Academy of Science, Arts, and Letters, v. 23, p. 427-440.

Dow, K.W., 1940, Some examples of ventifacts from Sleeping Bear Point, Leelanau County, Michigan: Papers of the Michigan Academy of Science, Arts, and Letters, v. 25, p. 473-476.

Farrand, W.R., and Bell, D.L., 1982, Quaternary Geology of Michigan, Michigan Geological Survey Map, scale 1:500,000.

Farrand and others, 1984, Quaternary geologic map of the Lake Superior 4 x 6 degree quadrangle: U.S. Geological Survey Miscellaneous Investigations Series Map I-1420 (NL-16).

Gates, D.M., 1939, A deposit of mammal bones under Sleeping Bear dune: Transactions of the Kansas Academy of Sciences, v. 42, p. 337-338.

Gates, F.C., 1950, The disappearing Sleeping Bear dune: Ecology, v. 31, n. 3, p. 386-92.

Handy, A.H., and Stark, J.R.,1984, Water Resources of Sleeping Bear Dunes National Lakeshore, Michigan, U.S. Geological Survey Water-Resources Investigations Report 83-4253, 39 p.

Holcombe, T.L., and others, 1996, Bathymetry of Lake Michigan, NOAA, World Data Center for Marine geology and geophysics Report MGG-11.

Jaffe, B. E., List, J., Hansen, M., and Hunter, R., 1993, Numerical modeling of shoreline change from longshore transport in the Platte Bay region, Lake Michigan, in List, J. H., ed., Large Scale Coastal Behavior '93, U. S. Geological Survey Open-File Report 93-381, p. 82-85.

Jaffe, B. E., Kayen, R. E., Gibbons, H., Hendley, J.W., Stauffer, P.H., 1998, Popular Beach disappears underwater in huge coastal landslide—Sleeping Bear Dunes, Michigan: U.S. Geological Survey Fact Sheet-020-98.

Jaffe, B. E., Kayen, R. E., Barnhardt, W. A., Reiss, T. E., Cochrane, Guy R., Yancho, S., and Holden, M., 2000, Recent huge landslides in the Sleeping Bear Dunes National Lakeshore, Michigan-- Implications for assessing coastal landslide hazards in the Parks, Geological Society of America Abstracts with Programs.

Kincare, 2000, Reassessment and correlation of Lake Algonquin shorelines in Michigan, absract in Great Lakes Geological Conference, Michigan Geological Survey Division.

Larsen, C.E., 1987, Geological history of Glacial Lake Algonquin and the upper Great Lakes: U.S. Geological Survey Bulletin 1801, 36 p.

Leverett, F. and Taylor, F.B., 1915. The Pleistocene of Indiana and Michigan and the history of the Great Lakes: U.S. Geological Survey Monograph 53, 529 p.

Loope, W.L., and Arbogast, A.F., 2000, Dominance of an ~150-year cycle of sand-supply change in late Holocene Dune-building along the eastern shore of Lake Michigan: Quaternary Research, v. 54, p. 414-422.

Milstein, R.L., 1987, Sleeping Bear Dunes National Lakeshore, Michigan, in Geological Society of America Centennial Field Guide-North Central Section, p. 303-306.

Milstein, R.L., 1987, Bedrock Geology of Michigan, Michigan Geological Survey Division.

Nash, D., 1980, Forms of bluffs degraded for different lengths of time in Emmet County, Michigan, U.S.A: Earth Surface Processes, v. 5 p. 331-345.

Pruitt, W.O., Jr., 1954, Additional Animal remains from under Sleeping Bear Dune, Leelanau County, Michigan: Papers of the Michigan Academy of Science, Arts, and Letters, v. 39, p. 253-256.

Thompson, T.A., and Baedke, S.J. 1997, Strand-plain evidence for late Holocene lake-level variations in Lake Michigan: Geological Society of America Bulletin, v. 109, p. 666-682.

Walbomm, T. E. and Larson, G.J., 1999, Surficial geology of Sleeping Bear Dunes National Lakeshore, Lake Michigan: a product of the USGS-EDMAP Program: Geological Society of America Abstracts with Programs,v. 31, n. 5, p. A-78.

Waterman, W.G., 1927: Ecology of Glen Lake and Sleeping Bear region: Papers of the Michigan Academy of Science, Arts, and Letters, v. 5, p. 351-375.

U.S. National Park Service, 1998, Sleeping Bear Dunes National Lakeshore: The Story of the Sand Dunes.



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The General park map handed out at the visitor center is available on the park's map webpage.

For information about topographic maps, geologic maps, and geologic data sets, please see the geologic maps page.

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A geology photo album for this park can be found here.

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Please visit the Geology Books and Media webpage for additional sources such as text books, theme books, CD ROMs, and technical reports.

Parks and Plates: The Geology of Our National Parks, Monuments & Seashores.
Lillie, Robert J., 2005.
W.W. Norton and Company.
ISBN 0-393-92407-6
9" x 10.75", paperback, 550 pages, full color throughout

The spectacular geology in our national parks provides the answers to many questions about the Earth. The answers can be appreciated through plate tectonics, an exciting way to understand the ongoing natural processes that sculpt our landscape. Parks and Plates is a visual and scientific voyage of discovery!

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For resources and information on teaching geology using National Park examples, see the Students & Teachers pages.
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