SHAPED BY WIND AND WATER Indiana Dunes National Park resides in a unique geologic setting at the southern tip of one of America’s largest freshwater lakes. A product of melting glacial ice, Lake Michigan is the last significant contribution of the Ice Age to northwestern Indiana. The expansive beach, rolling dunes, and wide wetland features illustrate the effects of water, wind, and vegetation growth in reshaping the surface of the land since the departure of the glacier from this region about 18,000 years ago.
E B Dune Sites O E L B O Foredunes are long ridges that L N A form parallel to the shoreline as G I W A H sand is saltated, or blown, onshore N C I I G by wind. Bowl-shaped blowout M A S E BE dunes extend landward owing to K LO A L IE the erosion of the foredune. E R A E S INDIANA T OHIO ILLINOIS W HIT E
SU BLOBE MIAMI SUBLOBE Vegetation Control
G RY Dune grasses are part of a sand WISCONSIN LA B DA CI OUN L AL dune’s first line of defense from IA C A erosion. Thriving in high winds, L G Y R these important plant species DA UN BO use fast-growing rhizomes to IN NS stabilize the sand and maintain CO Y IS CK the delicate ecosystem. W U
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Along the South Shore THE GEOLOGIC STORY Indiana Dunes National Park, located in Porter Dune Development County, is home to 2,182 acres of forested of Indiana Dunes The modern shoreline began when dune landscape along the southern shore of a small ridge of sand and gravel Lake Michigan. Part of the Northern Moraine National Park developed as lake levels rose about and Lake physiographic region, this area of 6,000 years ago. At 4,500 years, Indiana is characterized by glacial moraines, water level in Lake Michigan dropped natural lakes, and sand dunes. and sand was exposed and swept into U-shaped dunes and foredunes. During the past 3,500 years, these dunes have migrated and new ones Indiana Geological & Water Survey | Indiana University have formed, shaping the landscape 1001 E 10th St., Bloomington, IN 47405-2208 into what we see today. 812.855.7636 | [email protected] | igws.indiana.edu Photos provided by the Ind. Dept. of Natural Resources and Indiana Geological The Rises and Falls of Lake Michigan The rapid lake level drop 4,500 years ago dramati- cally changed the Tolleston Beach. As water level fell, As ice from the last major glaciation slowly retreated Big Blowout vast areas of sand were exposed and swept up by wind Paradise northward, several curved ridges of glacial sediment Furnessville Valley (called moraines) were left behind along the southern to form large, U-shaped dunes. The dunes migrated Blowout rim of a deep basin. Meltwater ponded between the away from the shore and obliquely landward into the lagoon, which by this time was becoming vegetated Tree moraines and the ice margin to produce early Lake Graveyard and changing into a fen wetland. It was at this time 10 Michigan. As the glacial margin fluctuated, channel 9 LAKE MICHIGANBeach House 9 that the Indiana Dunes area began to take on the Blowout TRAIL outlets opened and closed, influencing lake level in RTAGE PO AN character we see today. In the past 3,500 years, addi- LAKE MICHIGAN CAN BE DANGEROUS. INDI the basin. The rise and fall of the water level while For your safety, swim in guarded areas only. glacial ice was still in the basin produced many shore- tional sand has been blown into the Tolleston Beach Pets are strictly prohibited on Swimming Beach. 10 The lines along the southern rim of the lake. Only two by winds off the lake. This added sand resulted in Pinery 9 foredunes, the linear ridges that run parallel to Lake P D E 10 Dunes P S M T ROAD BOUNDARY PARK STATE E of these ancient shorelines were preserved as dune- Nature Michigan. Mt. Holden capped sandy ridges. Located south-southeast of the El. 184 ft. Preserve 7 8 2 park, Glenwood Beach (older) and Calumet Beach S O 8 Mt. Jackson El. 176 ft. Interdunal A Woody Wall of Defense Pavilion Devils Mt. Tom 9 Marsh mark the former shorelines of Lake Michigan approx- Beach Slide El. 192 ft. House 10 Sand dunes are usually thought of as transient fea- DNR BEACH imately 17,000 to 13,500 years ago. T 4 Nature Center Annex R N A A 7 8 City West IL TURE CENTE tures whose form and position are constantly chang- Property Shelter R TR To Michigan City, IN AIL EAST 300 N During the development of the younger Calumet Management Campground ing. Yet when vegetation takes hold, they can become Shelter North Orchard Beach, lake level was 30 to 40 feet higher than today. 3 Shelter 12 Gatehouse South-West reasonably stable landforms, as illustrated by the per- Shelter Wilson Starting 12,000 years ago, lake level began to fall very Shelter CALUMET TRAIL sistence of dunes formed thousands of years ago. Veg- Park rapidly as glacial ice retreated far enough northward 3 Oce Area 1 2 Property Duneside 2 etative control begins with the invasion of fast-grow- ek Area 2 Management re Shelter to open an outlet, allowing water to flow northward C Dunes es ing grasses, huckleberry, wintergreen, goldenrod, un Area 3 Camping Area Parking Prairie D Tremont across Ontario and into the St. Lawrence Seaway. Nissaki Youth Station Camp Store Picnic Area Nature Tent Camp and other ground cover. Once the sand becomes Entrance Station Picnic Shelter Lake Michigan’s water level fell more than 100 feet Preserve Main DUNES HIGHWAY relatively stable, species of willow, grape, and cherry Gate Wheelchair Accessible Dump Station and stayed low for about 2,000 years. At 9,400 years, Nature Center Restrooms soon appear and are followed by jack pine, aspen, and lake level slowly began to rise when the outlet to the Comfort Station Bird Observation Deck finally oak. The wind-shelter effect of the trees and 4 Trail Number Boardwalk north was elevated by the rebound of the earth’s crust. undergrowth, together with the holding power of 0 1/2 mile This water level rise reached current lake levels 6,000 EAST 25 N 12 their root systems, anchors the sand and results in the CALUMET TRAIL 0 1/2 kilometer NORTH years ago and continued to rise another 25 feet. Shaded relief has been dune types that are common in this area. exagerated 3x to show terrain. Ultimately, lake level peaked 4,500 years ago before immediately falling again. Over the next 1,000 years, To Burns Harbor, IN lake level fell almost 15 feet; the remaining lowering Blowouts and Migrating Dunes occurred slowly during the last 3,500 years. Blowouts usually begin as a narrow channel on the crest of the foredune where vegetation has been (like the tree graveyard at Big Blowout), reveal evidence of The Great Marsh removed by either foot traffic or nature. This confined Mountains of Sand older forests buried by dune migration between the early opening allows wind velocity to accelerate and create Landward of Tolleston Beach is an interdunal wet- A shoreline began building along the Indiana coast development of the Tolleston Beach and today. extreme erosion. Sand blown out of the foredune is land area called the Great Marsh. Initially a shallow, about 6,000 years ago. Sediment brought by water piled high atop the lee (landward) slope, creating a Migrating dunes form when sand supply suddenly open-water lagoon, this area changed into a series of currents accumulated in a small ridge with a land- bowl or amphitheater-like topography. Both Mt. Tom increases because of excessive wind erosion, an increase isolated marl ponds that vegetated over during the fall ward lagoon. As storms washed over the ridge, it grew and Mt. Holden, towering nearly 200 feet above the in beach width, or the sudden removal of vegetative from the peak lake level at 4,500 years ago Water-lov- larger and moved further landward. The upward beach, are examples of complexly developed blow- cover. Moving in the direction of the predominant wind, ing vegetation has accumulated throughout much of growth kept pace as the lake level rose. When lake outs. Beach House, Furnessville, and Big Blowout are migrating dunes can engulf entire forests. Dunes stabi- the area, producing up to 5 feet of peat. Trails 2 and level peaked, a dune-capped ridge of sand and gravel also typical of this type of dune. Long-buried trees, lize when sand supply diminishes, and vegetative control 10 offer good views of the marsh in contrast with the was deposited along the Indiana shore. Geologists call sometimes exhumed during blowout development is reestablished. densely wooded dunes around it. this new shoreline the Tolleston Beach. Maps: Indiana Geological & Water Survey.