Popular Beach Disappears Underwater in Huge Coastal

Landslide—Sleeping Bear Dunes, Michigan

On an unusually warm February morning in 1995, local resident George Weeks

was walking his dog along the shore in

Sleeping Bear Dunes National Lakeshore,

Michigan. Approaching Sleeping Bear

Point, he was shocked to find that where

there had only recently been a beautiful

beach was now a steep 100-foot drop into

Lake Michigan. The millions of cubic feet

of sand that made up the beach and part of

the high bluff above it had disappeared bewas sparsely populated and access to Sleeping Bear Point was difficult until after the

National Lakeshore was dedicated in 1977,

little attention was paid to these slides. In

1914, there was a U.S. Life-Saving Service

(later part of the U.S. Coast Guard) station

near the point to rescue mariners in distress.

A boat crew from the station had walked

across the 100-foot-high bluff at the point

only the day before the bluff’s face and

about 20 acres of land slumped into Lake

Michigan. Fifty-seven years later, in 1971,

a similar landslide occurred, and a bathymetric survey of the lake bottom off Sleeping Bear Point conducted shortly afterward

by the National Oceanic and Atmospheric

Administration (NOAA) found that this

slide had left a huge underwater hole.

In their work at Sleeping Bear Point

from 1989 to 1993, USGS scientists found

that water currents in the area transport sand

from southwest to northeast along the shore

of Lake Michigan. Once past the point, the

currents weaken and deposit sand along the

n February 1995, a 1,600-foot

Istretch of popular beach at

Sleeping Bear Dunes National

Lakeshore suddenly slid into the

waters of northeastern Lake Michigan. The National Park Service

(NPS) immediately requested the

assistance of the U.S. Geological

Survey (USGS) in evaluating the

hazard at the lakeshore. To protect

the public, USGS and NPS scientists are conducting studies that

will help predict when the landslide-prone area will move again.

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet-020-98

1998

U.S. Geological Survey (USGS) and National Park Service (NPS) scientists believe

that repeated coastal landsliding at Sleeping Bear Point may be related to increases

in fluid pressure in the spaces between the grains of sand (pore pressure) that make

up the bluff at the point. To test this idea, instruments to measure the pore pressure

(piezometers) have been installed within the bluff. Photo shows a USGS scientist

drilling a hole for a piezometer (inset).

neath the waters of the lake in a huge

coastal landslide. Luckily, no one was on

this popular beach when it slid.

Alerted by Mr. Weeks to the beach’s

disappearance, NPS rangers became concerned about the stability of the area and the

potential threat to public safety. The rangers

immediately posted signs warning park visitors of the possible hazard. They also asked

the USGS, which had conducted surveys of

the area from 1989 to 1993 as part of a

shoreline-change study, to investigate the

causes of the slide.

USGS scientists already knew that two

previous slides had occurred at Sleeping

Bear Point during this century—in December 1914 and March 1971. Because the area

SUPPORTING SOUND MANAGEMENT OF OUR COASTS AND SEAS

Three times this century, most recently in 1995, large parts of this bluff and the beach beneath it in Sleeping Bear

Dunes National Lakeshore, Michigan, suddenly disappeared beneath the waters of Lake Michigan in huge landslides.

To determine the causes of these slides, U.S. Geological Survey (USGS) scientists in 1997 studied the underwater part

of the 1995 slide from this 70-foot-long ship. The results of this and other ongoing studies will help USGS and National

Park Service (NPS) scientists identify times when slide danger is high and public access to this popular area should be

restricted. Inset photo shows a warning sign put up by NPS rangers immediately after the 1995 slide. (Ship photo

courtesy of Keith Vandervort, Traverse City Record Eagle.)

US SG
1995 slide deposit

SLEEPING 

BEAR 

POINT

Area removed in

landslide

Former coastline

Location

of tree

debris

N

0 1 MILE

0 1 KILOMETER

LAKE MICHIGAN

beach and just offshore. By comparing the

bottom topography with that charted in

1971 by NOAA, the scientists were able to

show that sand was gradually filling the underwater hole from the 1971 landslide at a

rate of more than 1.5 million cubic feet per

year. Because Sleeping Bear Point is an area

where sand is being steadily deposited, the

scientists concluded that the coastal

landsliding is not the result of erosional undercutting of the offshore slope by water

currents.

USGS and NPS scientists now believe

that the sliding at Sleeping Bear Point is

related to increases in fluid pressure in the

spaces between the grains of sand (pore

pressure) within the bluff. High pore pressure lessens the forces holding the sand

grains together, which may weaken the bluff

enough to trigger a slide. The pore pressure

may be increased by water from snowmelt

in winter being trapped behind the frozen

bluff face or within confined sand layers

beneath the bluff. This idea is supported by

the fact that all three known slides at Sleeping Bear Point happened in unseasonably

warm weather during winter months.

To gather the data required to test this

and other ideas about how landslides are

caused at Sleeping Bear Point, USGS scientists have installed instruments that monitor

pore pressure within the bluff and are also

using information from Global Positioning

System (GPS) satellites to detect any movement that might indicate instability. In 1997,

USGS scientists conducted a variety of

studies of the underwater part of the 1995

slide from a small ship. Near the shore they

found a deep hole where there had been a

gently sloping lake bottom. They also found

that a thick blanket of debris from the slide

extended more than 2 miles offshore into

water depths greater than 250 feet, much

farther and deeper than expected. Underwater video of the deeper part of the slide

showed trees protruding from the sand.

Bruce Jaffe, Robert Kayen, Helen Gibbons,

James W. Hendley II, and Peter H. Stauffer

Graphic design by

Sara Boore and Susan Mayfield

COOPERATING ORGANIZATION

National Park Service

These trees had been growing on the bluff at

Sleeping Bear Point and had been swept

into deep water with the slide.

The results of these studies will help

USGS and NPS scientists identify times

when the slide danger at Sleeping Bear

Point is high and access should be restricted. The information from the studies

will also be used to educate and warn the

public about the hazard at the point. Eventually, most monitoring functions will be

transferred to the NPS, so that rangers can

detect and quickly respond to any increase

in the slide hazard. In addition, USGS biologists are conducting studies of the ongoing effects of the slide on fish and other

aquatic life in the National Lakeshore.

The cooperative efforts of USGS scientists and the NPS at Sleeping Bear Dunes

National Lakeshore not only are advancing

understanding of coastal and underwater

landslides in the Great Lakes region but also

are providing new insights into how such

landslides occur in other coastal areas. The

work of these USGS scientists is only part

of the USGS Coastal and Marine Geology

Program’s ongoing efforts to protect

people’s lives and property from geologic

and environmental hazards in the coastal

zones of the United States.

Coastal landsliding at Sleeping Bear Point may be related to increases in fluid pressure in the spaces between grains

of sand (pore pressure). High pore pressure lessens the forces holding sand grains together, which may weaken the

bluff at Sleeping Bear Point enough to trigger a slide. Pore pressure may be increased by water from snowmelt in

winter being trapped behind the frozen bluff face or within sand layers confined by impermeable clay beneath the

bluff. This idea is supported by the fact that all three known slides at Sleeping Bear Point (1914, 1971, 1995) happened

in unseasonably warm weather during winter months.

More than 35 million cubic feet

of sand disappeared beneath

the waters of Lake Michigan in

a huge coastal landslide at

Sleeping Bear Point in 1995.

This composite image shows

both the onshore and offshore

areas removed from the point

in that slide. In 1997, U.S.

Geological Survey scientists

found a thick blanket of debris

from the slide extending more

than 2 miles offshore, much

farther than expected.

Underwater video of the

deeper part of the slide

showed trees protruding from

the sand (inset photo). These

trees had been growing on the

bluff at Sleeping Bear Point

and were swept into deep

water with the slide.

MILWAUKEE

SLEEPING BEAR 

DUNES

NATIONAL 

LAKESHORE

CHICAGO

LAKE MICHIGAN

0 50 MI

0 50 KM

WISCONSIN

ILLINOIS

MICHIGAN

MICHIGAN

INDIANA OHIO

   yyy yyy yyy yyyyy

   yyyyyy yyyyyy yyyyyy yyyyyy

Before 1995 After 1995

Pore-water pressure—

 larger size indicates

 greater pressure

Water flow

Impermeable clay

Summer water table

Lost in slide

Slide deposits

Winter water table during warm interval

Impermeable clay Impermeable clay

Impermeable clay

Frozen bluff face

Beach

Melting snow

Old face

For more information contact:

U.S. Geological Survey, MS-999

345 Middlefield Road

Menlo Park, CA 94025

(650) 329-5042

http://marine.usgs.gov/

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