The greatest of the
Great Lakes goes
by different names:
Lac Supérieur
SUPERIOR
Gitche Gumee
Truly Superior measures
Surface Area
31,700 mi² (82,100 km²)
The size of the state of Maine
Volume
Roughly 3-quadrillion gallons
(2900 mi³ (12,100 km³))
Enough to cover North and South America
in one foot of water
Average Depth
483 ft (147 m)
About the distance between Lake Superior
and Duluth’s hilltop
Maximum Depth
1,332 ft (406 m)
The same as one lap around a
standard track
Length
350 mi (560 km)
A drive from Two Harbors to Madison
Breadth
160 mi (260 km)
A drive from Duluth to Minneapolis
Shoreline Length
1,826 mi (2,938 km)
A drive from Duluth to Miami
Retention Time
191 years
The average drop of water entered when
Fort Snelling was a frontier outpost and
Minneapolis didn’t exist.
Water
Lake Superior holds 10% of the world’s fresh
surface water that is not frozen in a glacier
or ice cap. The water level of this inland sea
depends on precipitation and the season. Typically, the lake is just over a foot (32 cm) higher
in September than it is in March.
or high barometric pressure pushes water
to one side and then quits pushing. In Lake
Superior, seiches take roughly 8 hours to cross
the basin and come back again, sometimes
changing nearshore water levels by more than
3 ft (91 cm).
The lake’s water budget reflects about a 4-foot
(125-cm) exchange of incoming and outgoing
water each year. Superior has a relatively small
watershed (49,300 mi2, 127,700 km2) for its
size. This watershed is laced with streams that
feed Lake Superior’s 848 tributaries.
Lake Superior is exceptionally cold (an average
of 40 °F (4 °C)) but it is still swimmable in
summer when the surface water warms. Since
glaciers carved away much of the soil, Lake
Superior is also relatively unproductive (oligotrophic). With little in the way of plant nutrients and large amounts of dissolved oxygen,
some scientists have called Lake Superior “a
distilled water ice bath.” Underwater visibility
can exceed 75 ft (23 m).
Water has basically two ways out of Lake Superior: a right exit or up. Lake Superior spills
toward the Atlantic Ocean through the Soo
Locks on the St. Marys River. This eastern exit
is about 600 ft (180m) above sea level. Contrary to what one might guess, Lake Superior
evaporates fastest from October to February
when dry cold air from Canada moves over the
warmer surface of Lake Superior soaking up
water like a sponge.
Seiches mask Superior’s tiny tide. Seiches
slosh through Lake Superior’s basin after wind
Most of the chemical pollutants in Lake
Superior (such as mercury, dioxin, and PCBs)
fall from the atmosphere with precipitation or
dust. Even though the concentrations of these
toxins are relatively low compared to the other
Great Lakes, they can accumulate through the
aquatic food web and harm top predators, like
bald eagles and humans.
Water In
Water Out
Over-lake precipitation
(876,564 ft 3 /sec)
Through the St. Marys
River (957,732 ft 3 /sec)
Rivers and streams
(667,428 ft 3 /sec)
Evaporation (mainly in
winter) (650,796 ft 3 /sec)
Diversions redirecting
water that would normally
flow into Hudson Bay
(65,364 ft 3 /sec)
Lake Superior…
Fast Facts
Over the years,
however, the lake has
consistently been one thing:
gichigami
 is the largest freshwater lake in the
world by surface area and the third
largest by volume (Lake Baikal in
Siberia and Lake Tanganyika in East
Africa contain more water).
 could hold all the water in the other
Great Lakes, plus THREE MORE
Lake Eries.
 connects the heart of North America
to a global economy.
 is remarkably clean and cold.
 is a geological newcomer
(only about 10,000 years old).
 is exhibiting a trend in summer
surface temperature. Per decade
since 1980, surface water
temperature in summer has
increased about 2 °F (1 °C), while
regional air temperature has
increased 1 °F (0.5 °C).
 is managed through a binational
agreement involving Canada and
the U.S., and by the Province of
Ontario and the states of Minnesota,
Wisconsin, and Michigan.
 has rip currents that are dangerous
to swimmers.
SUPERIOR
FACTS
3-quadrillion gallons, one Great Lake
Terms
Seiche: (pronounced “saysh”) Also called a
slosh. These “free standing-wave oscillations”
rocking back and forth across lakes are created by wind or air pressure. You can set up a
similar motion in your bathtub by sliding back
and forth.
Oligotrophic: Very unproductive; lakes low in
nutrients and algae, usually very transparent
with abundant oxygen.
Soo Locks: A set of 5 locks on the St.
Marys River separating Lake Superior
and Lake Huron.
Lakers: They’re not a basketball team! They’re
ships designed especially for transport on the
Great Lakes.
Salties: Ocean-going vessels from all over
the world.
Lake Effect: The ability of a large lake to
modify the local weather.
Lake Superior Agate: Minnesota’s official state
gemstone. Quartz stones banded with rich
reds and oranges (derived from iron ore in the
soil) formed in the gas pockets of lava flows.
Glaciers dispersed them in the last Ice Age.
Taconite: Sedimentary rock mined for its iron
content of 25-30%. It is an important source of
raw material for making steel.
Citation and Credits
Habermann, R., S. Moen, and E. Stykel. 2012. Superior Facts. Minnesota Sea Grant (pub. S25),
Duluth, Minn.
Banner Photo Credits:
1: Chris J. Benson, 3,7: Jeff Gunderson, 2: Elizabeth LaPorte (MISG), 4: A. Muir (GLFC),
5: T. Lawrence, (GLFC), 6: U.S. Fish & Wildlife Service
Connect with us…
Minnesota Sea Grant
University of Minnesota Duluth
132 Chester Park
31 West College Street
Duluth, MN 55812
Phone: 218-726-8106
E-mail: [email protected]
Web: www.seagrant.umn.edu
Photo: Chris J. Benson
www.seagrant.umn.edu
Climate
Shipping
Climate is the set of meteorological conditions that prevail in a region over time. Lake Superior’s climate reflects its position on the planet and, to a smaller degree, the heat storage capacity
of all the water it contains. It’s in the cool part of North America’s temperate zone where summers average about 70 °F (21 °C) and winters involve snow, parkas, and temperatures well below
0 °F (-18 °C). Of the roughly 30 inches (76 cm) of precipitation that hits the lake each year, most
falls between May and October. Collisions between belts of low and high pressure from the Gulf
of Mexico and Canada generate the region’s wildest storms and blizzards.
From mid-March to mid-January the Soo Locks
are open and Lake Superior supports an active
maritime industry. The “Great Lakes Bulk Cargo
Capital” of Duluth/Superior is one of the busiest
inland ports in the United States. Each year the
port handles about 1,000 ships carrying 42-million
tons (38 metric tons) worth $1.9 billion. The largest of these ships, the lakers, are typically 1,000
ft (300 m) long and 105 ft (32 m) wide. They can’t
fit through the Welland Canal, so they will never
ply the oceans. Mainly they carry coal and iron ore.
Salties are ocean-going vessels. About 100 times
per year a saltie makes the seven-day, 16-lock,
2,342-mile trip from the Atlantic Ocean through the
Great Lakes-St. Lawrence Seaway to the Duluth/
Superior Harbor to pick up grain, to drop off windenergy equipment, or to conduct other business.
Scientists report that Lake Superior is responding to a
global climate trend as clearly as anywhere on Earth.
They’ve documented:
 A decline in ice cover (Down by 79% since the 1970s).
 An increase in surface water temperatures (Summer
water surface temperatures have risen about 2 °F (1 °C)
per decade since the 1980s).
 Faster winds (Wind speeds have increased over the lake
by nearly 5% per decade since the 1980s).
Photo: Jeff Gunderson
 The regional trend is toward warmer temperatures, and
increases in extreme storms and droughts. Winter and
spring are showing signs of becoming wetter while summer and fall are showing signs of becoming drier.
Weather
The “lake effect” can also super-size storms
by adding moisture and speed to wind passing
over the lake. Michigan’s Upper Peninsula is
typically buried under six times more snow
each year than downtown Duluth because of
the lake effect. In summer, a dome of high
pressure can form over the lake pushing approaching storms to the southeast.
The dangerous “Gales of November” occur in
autumn when low-pressure systems pass over
the lake. Wind speeds can easily reach 50 mph
and gusts can exceed 100 mph.
Lake effect
snow heading
south-east
Photo: NASA’s Earth Observatory
Fog hides Duluth under a heavy blanket for 52
days in an average year (by comparison, Minneapolis averages 11 days). Fog forms when temperature and dewpoint differ by less than 4 °F (2.5 °C). As the moisture in warm air condenses
over the colder surface waters, advection fog rolls into Lake Superior’s coastal communities. Sea
smoke occurs when seriously cold air moves over relatively warmer water during winter.
40%
40%
Principal Cargos By Tonnage (average)
Iron Ore: (in the form of taconite pellets) from Minnesota’s
Iron Range to steel mills
Coal: from Montana and Wyoming to utilities and industries on the lower Great Lakes
Grain: from the Midwest to Europe and Africa
Other: Shipments of limestone, salt, cement, along with
general freight and specialty cargos (like wind turbines)
1 billion years ago: Molten basalt
erupts from the Mid-Continent
Rift. The rifting lasts for about 20
million years.
Fish
1
Non-native species: 17
Non-native, non-reproducing species: 2
(American eel and Atlantic salmon)
Lake Superior has bragging rights when it comes
to fish. Although it produces far fewer fish than
the other Great Lakes, it supports a robust suite of
native species. Sustainable management practices have fostered a modern and commercially
important fisheries industry after overfishing and
the introduction of invasive species jeopardized it
during the mid-1900s. Commercially caught fish
include ciscoes (lake herring), chubs (deepwater
ciscoes), lake whitefish, lake trout, and the nonnative rainbow smelt. Lake Superior also supports
a strong charter fishing industry and sportfishing opportunities focused on several species of
salmon and trout.
Lake Superior’s ciscoes1 were called lake herring by Scandinavian settlers, who thought they
resembled ocean herring. Particularly during the
spawning run in November, commercial fishermen
harvest ciscoes for fillets, gefilte fish, and caviar
500 million
years ago:
The area
stabilizes.
Summer brings boaters, sightseers, campers,
kayakers, anglers, and even swimming sunbathers to the shore. Beachgoers should know how
to escape from the rip currents that can form
along Lake Superior’s south shore. Known for
its clean water, Lake Superior’s water is a Midwest SCUBA diving epicenter for sunken ships.
In June, runners from around the world vie to
win “Grandma’s Marathon.”
Photo: MN Sea Grant
Winter excites skiers, snowmobilers, snowshoers, and ice fishing fans. The Bayfield sea caves
near the Apostle Islands in Wisconsin are worth
a trek during years with enough ice cover. Every
January, thousands gather along Minnesota’s
North Shore to cheer on the dogs and the
mushers during the John Beargrease Sled Dog
Marathon, a 400-mile journey that re-traces part
of the region’s history. All recreationists, but especially those who venture out in winter, should
dress and behave to avoid hypothermia.
Non-Native
2
3
destined for national and international markets.
Ciscoes are a fantastic source of omega-3 fatty
acids and are a regional smokehouse and restaurant favorite.
Lake whitefish live in deep waters mainly along
Lake Superior’s South Shore. Lake whitefish
are prized for their delicate fillets and, like
ciscoes, are lower on the food chain than lake
trout and consequentially contain fewer bioaccumulative toxins.
2
Lake trout 3 have made an astonishing recovery
since their near-extinction in the late 1960s. If it
weren’t for the sea lamprey control program run
by Canada and the U.S., Lake Superior’s lean lake
trout would not be on regional menus or available
for sport fishing. The most abundant form of lake
trout is the deep-dwelling siscowet.
When commercial fishing was in its heyday,
lake sturgeon 4 were hard-hit. Today, commercial
harvest is prohibited and First Nations are only
allowed to use them for ceremonial purposes.
Lake sturgeon primarily swim in larger Canadian
tributaries but restoration efforts in the St. Louis
Created by Fire & Ice
950 million years ago: A blanket of basalt
up to 10 mi (16 km) thick slowly sinks into
the earth creating the Lake Superior basin.
Ancient rivers deposit the rocks that make
up the Apostle Islands, Bayfield Peninsula,
and Pictured Rocks National Park.
Tourism is one of the economic mainstays of
the Lake Superior region, which is home to
over 600,000 people (474,150 Americans and
155,675 Canadians). An abundance of festivals,
concerts, events, and unique dining and shopping opportunities create a cheerful atmosphere,
particularly in Lake Superior’s two metro areas:
Duluth, Minnesota, and Thunder Bay, Ontario.
10%
NATIVE
Native species: 38
Weather is the state of the atmosphere with respect to current temperature, precipitation, wind,
and cloudiness. Lake Superior can modify the daily weather through a phenomenon known as
“lake effect.” Compared to inland temperatures, shoreline temperatures can be noticeably
warmer in winter and much cooler in summer. This is because water is slower to absorb and
release heat than land.
Recreation
10%
2.5 million years ago:
Ice Age! Ice sculpts the
basin into its present
shape through glacial
and interglacial periods.
11,000 years ago: Glacial Lake Duluth,
the precursor to Lake Superior, forms as
the ice sheet retreats northeastward. The
lake’s torrential outflow near present-day
Duluth carves the St. Croix River Valley
and feeds the Mississippi River.
4
SPECIES
estuary seem to be paying off with the sighting
of fry in 2011.
non-native Species
Non-native species have influenced the greatest
of the Great Lakes since the early 1900s when
rainbow trout and brown trout were intentionally
introduced. From parasites to plants to fish, 71
non-native species are now reproducing in Lake
Superior. An additional 24 non-native plants
grow along Lake Superior’s shores.
Currently, the worst Lake Superior offender is
the sea lamprey.5 In vampirish fashion, they
attach to large fish and suck their blood and
body fluids out. They can consume roughly
40 lbs (18 kg) of fish in 12 to 18 months. Sea
lamprey arrived in the upper Great Lakes once
the Welland Canal allowed them to swim around
Niagara Falls. The U.S. and Canada spend about
$16 million annually to keep them in check in the
Great Lakes.
5
6
the Duluth Superior Harbor along with dozens of
species that were likely brought into the Great
Lakes through ballast water.
During the 1970s, introduced rainbow smelt7
were the most abundant fish in Lake Superior.
Fisheries experts aren’t sure exactly why, but
the smelt population crashed in 1979 and has
stayed low ever since. Undaunted, smelters still
brave cold Superior nights to net them as an
annual rite of spring.
Non-native species can damage the environment
as well as local economies. Do your part to
prevent the spread of non-native species. Don’t
release animals and plants into a body of water
unless they came out of that body of water. Be
sure to clean your boat and gear before leaving a
lake, river or stream.
Zebra mussels 6 and their cousins, quagga
mussels, don’t plague Lake Superior like they
do the other Great Lakes. However, they occupy
10,000 years ago: During the retreat
of glacial ice, western Lake Superior
fluctuates, rising 500 ft (152 m) above
or falling 250 ft (76 m) below its current
level. Eventually, the St. Marys River
becomes Superior’s outflow, and the
water level eases to its present state.
Paleo-Indian people move into the
Lake Superior region.
Today: The basin continues to spring
back after being squashed by the
last glacier. This “isostatic rebound”
is greatest along Canadian shores,
which are rising about 18 in (46 cm)
per century. Lake levels continue
to fluctuate.
7