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il
Changes of Level of the Great Lakes.
By G. K. GILBE^IT.
Reprinted from the new review, The Forumjj^Q^^ 5 Jurf 1388
^^\
**
\v
CHANGES OF LEVEL OF THE GREAT LAKEa
The following pages are devoted to the physical history of
the lakes of the northern States. As avenues of commerce, as
preserves of food fishes, as reservoirs of pAre water, as resorts
for the artist, the pleasure seek'er, and the health seeker, their
description is left to other pens. They are here treated only as
physical features, the endeavor being to set forth their origin and
the series of physical changes, past, present, and future, that
constitute their history.
Rivers are the mortal enemies of lakes. The river that flows
into a lake brings st<jnes and sand and fine mud, and dropping
these into the quiet water endeavors to fill the earth cup that
holds it The year's tribute of sediment may have as little
apparent effect as the year's tribute of water, which quietly
escapes to atmosphere and ocean ; but the river is long of life and
steadfast of purpose, and if years and centuries prove too short,
it resolutely persists through geologic ages. The river that
flows away from a lake constantly deepens its channel of escape,
and thus attacks the lake's rampart at its weakest point If
the rampart is of loose earth, this is roiled and floated away bit
by bit, and the work goes on merrily ; if it is of firm rock, this
is dissolved, and then the process is exceedingly slow. But time
is long, and even by solution the rampart ma\^ be channeled to
its base and the whole lake drained away.
Nevertheless, in spite of this warfare of extermination, waged
in all lands and through all time, there continue to be lakes, and
so there must be in nature lake-producing as well as lake-destroy-
ing agencies. There are indeed many such, but a few only need
V)e appealed to to explain the great majority of lakes, and the
chief are upheaval and glaciation.
, Some parts of the earth's surface are known to be rising and
others to be sinking. Usually such changes are of impercepti-
418
CHANGES OF l.EVKL OK TIIK GREAT LAKES.
ble slo\vn<v*s, but ocoaaionally there is u sudden movement of a
few feet, involving rupture of rocks and an earthquake Similar
movements luive abounded tlirough past ages of the eartli, and
to them are due not only mountains and piateaus, but eontinenta
and ocean beds. This great natural process of uplift and down-
throw tends to produce lake basins, and, as we have seen, its
tendency is opposed by the great natural })rocess of erosion and
deposition by rivers. The two are so nearly balanced that the
scale is thrown to one side or the other by the accident of climate.
Where much rain falls the rivers are powerful and prevail,
sawing gorges through ridges as fast as they rise, building up
the floors of valleys as fast as they sink. Where little rain falls
the streams are weak, and the displacement of the earth's crust
shapes the land into lake basins. Where the least rain falls the
basins are many, but the lakes are ephemeral, created by the
storm and dissipated by the sunshine. Great Salt Lake, Utah
and Humboldt Lakes, and a score of others in our arid belt lie in
valleys shaped by crustal displacement
A glacier is aptly called a river of ice. Like a river of water
it has an upper surface sloping continuously from source to goal,
and like a river of water it rests on an uneven bed of its own
shaping. When an aqueous river is suddenly deprived of its
supply of water, there remain along its channel a series of pools
recording the inequalities of erosion. When a great glacier is
melted away the inequalities of its erosion are recorded in a chain
of lakes. Moreover, much of the .naterial ground and torn by
the glacier from its bed is carried forward in the ice and dropped
in a long heap where the ice melts, constituting a moraine. If
the final melting is gradual, a series of moraines partitions the
valley, creating lake basins. While it is building a moraine,
the ice front advances and retreats in response to small changes
in climate, so that the dropping of detritus is irregular, and the
surface of the moraine is made billowy, abounding in small lake
basins. Thus from glacial erosion there arise rock-basin lakes,
and from glacial deposition of detritus there arise moraine-
dammed lakes and moraine lakes.
In that wonderful geologic winter known as the Age of Ice,
the annual snowfall on the northern part of our continent was
CHANGES OF I.EVKL OF THE GREAT LAKES.
419
HO groat and the annual melting was bo small that the snow
accumulated year by year, and became cemented into a continu-
ous, deep, and over-growing sheet of ice. As the depth of the
sheet increased the Pressure of its own weight became finally
insupportable, and there was relief by horizontal flow, the mar-
gin moving outward to a region of warmer climate, where it was
molted. It was, in fact, a vast glacier, so vast that the figure of
.speech emlxxlied in the title " river of ice " becomes here inapt
Instead of flowing from a mountain down a sloping valley, it
flowed radially from a central plateau of ice, with little regard
for the slopes of the land over which it passed. We do not yet
know the center of dispersion, but the ice entered our land as
an invader from Canada. The border States from Maine to
Minnesota were overrun, and most of the land north of the Ohio
and Missouri Rivers. Twice the van was pushed far into the
domain of the sun, and twice it was compelled to retreat ; but
when the sun finally surveyed its reconquered territory, the land
was no longer simply graven with a tracery of rivers ; it sparkled
with the sheen of innumerable lakes.
Wherever the ice moved it swc^pt forward the soil and all
other loose material, and with them scoured the firm rock be-
neath, producing a polished surface of peculiar character, with
many scratches and furrows parallel to the direction of motion.
In some regions it did little more than this, but elsewhere it was
a powerful agent of erosion, scooping out great hollows from the
solid rock. For some reason not clearly understood the erosion
was greatest along a zone parallel to the margin and a few hun-
dred miles back from it, and here were formed the basins not
only of the Laurentian lakes from Ontario to Superior, but
of Winnipeg, Athabasca, Great Slave, and Great Bear Lakea
Within this zone of greater erosion the points of greatest erosion
were determined chiefly by the pre-glacial shape of the surface.
Where the land was high the overriding ice sheet was relatively
thin, its motion correspondingly slow, its pressure slight, and its
erosion unimportant Where the land was low the deeper ice
stream flowed faster, pressed harder on its bed, and eroded rap-
idly. How deep the original valleys were cannot be told, for
the details of the old toj)ography have been ground away, but
28
u
4*^0
CHAMGKS OP LEVEL OP TUE (IKEAT LAKES.
•we may be sure that they were shallow ns compared to the exist-
ing troughs. The deptlis of Lake^ Michigan, Superior, un«l
Ontario reach from three hundred to five huiidre<l feet below the
level of the ocean, and their origin cannot be referred to stream
erosion alone without incredible assumptions as to continental
elevation.
Between the Great Lakes and over the country south of them
are spread moraines and other deposits of ice-transported debris.
They vary gre^itly in coni[)<)sition, structure, and topographic
form, but have this in common, that their material differs in
kind from the solid rock immediately beneath it, having been
brought from more northerly points. Collectively they are called
the Drift, and they dominate the s\irface, ofteti concealing the
rock for scores of miloi. The typical morainic drift has a hum-
mocky surface, abounding in small lake basins called '-kettles;"
other varieties undulate more gently, and harbor broader but
shallow lakes; and elsewhere the surface is smooth and com-
pletely drained. Over large districts, especially north of the
Great Lakes, the drift is scant and irregularly spread upon an
uneven rock surface, and there lakes are especially abundant
Many of them lie in rock basins, but the most are partly con-
tained by walls of drift.
The Great Lakes, with the possible exception of Erie, all
occupy rock basins, that is to say, they lie in hollows having
continuous rims of solid rock ; but these rims are in places coped
by accumulations of drift in such way as to increase the depths
and areas of the lakes and control to some extent the direction
of their outflow. It is probable that the surplus waters of Supe-
rior and Ontario escape over the lowest points of their rocky
rims, but if the drift were removed at the south end of Michigan
the lake would find a lower outlet and become tributary to the
Mississippi. The removal of drift between Huron and Erie
would probably render them confluent, as Huron and Michigan
now are. The removal of drift between Erie and Ontario would
greatly reduce the upper lake, or possibly drain it completely,
and would make it tributary to the lower at Hamilton, Canada,
instead of at Fort Niagara.
As soon as the ice was gone running water began a work of
^fm
CHANGES OP LEVEL OP THE QKEAT LAKES.
421
reclamation, waHhing the earth from the steeper slopes down into
the lakelets, and cutting down their otitlets until they became
so shallow that vegetati»)n could take up the work and liil them
to the top with peat, llalf of the moraine lakes have been thus
converte<l into marshes, and throtigh extensive districts in Ohio,
Indiana, and Illinois only the marshes, and the deposits of peat
and marl where marshes have been drained, remain to show how
numerous were the lakes. The <lrift-dainmed lakes are better
preserved, partly because in. their region there is less loose debris
•with which t<i till them, partly because their outflow is often
across resistant rock. Of progress toward the destruction of the
Great Lakes there will bo occasion to speak in another connec-
tion.
But the story of the lakes is not completely told by explain-
ing the origin of their basins; there is also a history of their
development as water bo<li£». During the period of greatest
ice expansion the hydrographic basin of the Great Lakes and
the valley of the St Lawrence were not merely ^'led but over-
passed, so that the rivers generated on the glacier in summer fell
from its southern edge beyond the rim of the Great- Lake basin,
and flowed to the Missouri, the Mississippi, the Ohio, the Sus-
quehanna, and the Delaware. As encroaching heat gradually
reduced the limits of the ice, its retreating margin reached and
passed the basin rim at various j)oints, and there accumulated
between the water parting and the ice wall a series of glacial
lakes, fed by the melting ice and discharging southward across
the passes of the great divide. The precise order of events has
not been made out, but there was a time when the western part
of the Superior basin contained a lake discharging to the Missis-
sippi River by way of the St. Croix, there was a time when
the southern part of the Michigan basin held a lake discharging
to the Mississippi by way of the Des Plaines and the Illinois, and
there was a time when a lake, occupying the western half of the
Erie basin and covering the Maumee valley, overflowed at Fort
"Wayne to the Wabash Hiver, and thus sent its water to the
Ohio. At a later stage a single sheet of water covered the south-
ern yjart of the Huron basin and all the Erie, and encroached
slightly on the Ontario. Then the ice retreated from all the
422
cuANuES OP lkve;;. of the great lakes.
Ontario basin, hut rernaimHl in tlie vallev of the St. Lawrence,
pressing against the Adironihiek u])lau(lH. By this retreat Erie
and Ontario were ditFerentiated, and the Niagara Uiver came
into existence^; hut, as wo sliall stn;, tlie map was far from a.><8Uin-
ing its present aspect. The; water of ()iil;iriu, liaviiig no eseape
by way of tlie St. Lawrence valley, sought the lowest pass
south of tlie Adirondacks, finding it wl jre tlui engineers of the
Erie Canal afterward found it, and overflowing at Jtome to the
Mohawk Jiiver. This discharge was maintained for a long
period, giving the waves time to construct massive beaches and
carve broad terraces which still endure. They have been traced
all about the basin, except, of course, on the northeast, where
the waves broke vainly on an unre(;ording wall of ice. The
" Kidge Road" from Lewiston to Sod us follows the crest of one
of these beaches; a railway from Richland to Watertown has
found easy grades along the base of another.
It is impossible, witjiin the limits of a magazine article, to
assemble or even cite the documents on which this historical
sketch is founded ; but it may be stated, in brief, that they con-
sist of deserted shore lines, deserted river channels, muddy lake
sediments enveloping bowlders dropped from icebergs, and old
stream valleys flooded by encroaching lakes. One of the most
important bodies of evidence is educed by measuring the height
of the same shore line at different points. Originally the shores
were horizontal, of course, each at its own level, but they are not
so now. They rise t<)ward the north, and, less rapidly, toward
the east ; and we learn thereby that when they were made the
face of the land had a different attitude, being lower at the north
and east, as though depressed by the weight of the ice.
^t the epoch of the separation of Erie and Ontario the north-
ward tilting of the land exceeded three hundred feet in the length
of Ontario, and amounted to half as much in the length of Erie.
The northeastern end of Erie being fixed in height, as it still is,"
by the outlet at Buffalo, the plane of its level surface cut the
western slopes of the basin at a lower point, and the lake was
smaller. It was, indeed, only one-third as long as now, and its
water surface but one-fifth as great The sites of Toledo and
Cleveland were far inland, and the Bass Islands were smooth
COANGES OP LEVEL OP THE GREAT LAKES.
42'i
liilla in the Mauinee valley. Finally the bk)cka(le w&a raised, in
the St Lawn.Mice valley, the outlet of Ontario wa.s shifted from
Home to the Thousand Islands, and it<^ water level was drawn
down five hundred feet During the Home epoch of its hintory
Ontario's area was 60 per eent greater than now ; it began the
Thousand-Island epoch with an area 30 per cent smaller than
now.
While yet the glacier was present and the navy of Ontario
was a fleet of icebergs, the depressed land at the north had begun
to rise again. When the glacier was quite gone the reflux was
rapid, the land s(>on reached a more stable position, and the
lakes iicquired their present dimensions. Had the oscillation
receive<l no check, our hydrography &iu[ avenues of commerce
might have been very different; a further tilting of the land to
the extent of three inches in each mile would send a great river
from Chicago to the Mississippi, reverse the current in the
Detroit, stop Niagara Falls, anu rob the upper St Lawrence of
seven-eighths of its water.
Has the oscillation ceased? Is Niagara destined to run dry?
These are questions hard to answer for the remote future into
which science fain would peer, but less difficult as concerns
those few generations of posterity to which our ambitions and
sympathies extend. It is one of the inducti'^ns of geology that
absolute stability is a myth, and all j)arts of the earth's crust
continually undergo changes of level. There is no reason to
believe that the lake district is an exception to this law, but
whatever movements may be there in progress are so slow that
the}' have not been detected, and their tendency is unknown.
In our use of the lake harbors we have observed no changes
requiring earth movements for their explanation, and this nega-
tive testimony, so far as it goes, shows present stability. That
which the waves have done to the present coasts, in the cutting
back of cliffs and the building of spits, is a work of many centu-
ries, during which the water level must have remained nearly
constant; and the practical stability thus shown for the imme-
diate past is a guarantee for the immediate future.
There is no question that changes of other kinds are in prog-
ress Storm waves and storm currents are eating away the coasts
-rMnm^vrmrtmm
434
CHANGES OP LEVEL OP THE GREAT LAKES.
and spreading the fine debris over the lake bottoms, where it
mingles with the muddy tribute brought by flooded rivers ; the
St Clair River is feebly scouring its channel and building ita
delta; the Falls of Niagara are gnawing back toward Lake Erie
at the rate of four or five hundred feet in a century ; and with
infinite slowness the Ste. Marie, Detroit, and St. Lawrence Rivers
are deepening their rocky beds. In a future geologic age all
the lakes that survive the erosion of outlets will have succumbed
to filling by alluvial mud, and the reign of running water will
once more be established.
But the lake basins are' so capacious that we become aware
of their slow filling only by observing the discoloration of the
water in times of freshet and of storm. The scour of the St. '
Clair can do ro more than reduce the level of Lake Huron to
that of Lake St. Clair, a difference of two or three feet; and as
the reduction proceeds, its rate, now exceedingly slow, must con-
tinually diminish. If the recession of Niagara Falls were to
continue at its present rate. Lake Erie would be tapped in two
hundred centuries ; but the rate is determined by the geologic
stnicture, and that structure changes between Goat Island and
Buffalo in such a way as to retard the work of erosion.
All these processes are too slow to affect our hopes or fears
concerning the immediate future, and for our posterity in the
year 20,000 we have no solicitude. The men who shall watch
the draining of Lake Erie — or who, perchance, shall find it
worth their while to prevent it — wiU as far surpass us in powers
and resources as we surpass the men who watched the lake's
creation. For all practical purposes our inland seas are perma-
nent and their basins stable. The only modifications that affect
our economy are those wrought by the waves upon their coasts.
Nevertheless, their stability is sometimes called in question.
Their levels are not absolutely constant, but oscillate under
various influences about a mean position, and when they are
unusually low the "oldest inhabitant " is interviewed, and is
reported to declare that the like was never seen before. Then .
some theory of permanent change is promulgated and the sensa-
tion has its day. While yet the newspaper discussion of the
recent lowering of water levels is fresh in memory it will not be
CHANGES OF LEVEL OP THE GREAT LAKES.
425
amiss to recite briefly the conditions on which such changes
depend.
About each of the lakes is a district of land draining toward
it. A portion of the rain and snow falling upon this land is
returned to the atmosphere by evaporation from the soil, and a
larger portion is returned by evaporation from the surfaces of
plants. The remainder flows to the lake and tends to raise its
level. Its level is also raised by the rain and snow falling upon
it. On the other hand, its level is lowered by evaporation, and is
lowered by the discharge through the outflowing river. In the
long run the supply from inflow and rain is balarced by the loss
through evaporation and outflow, and so in a general way the
lake altitude is constant; but in detail it is inconstant, oscillating
about its average position.
The additions to the lake by rain are not uniform through the
year, but are usually greater in summer. The additions from
tributary streams are still less uniform, being smallest in winter,
when precipitation takes the form of snow, and largest in spring,
while the snows are melting. The loss from evaporation is like-
wise unequal, varying with the temperatures of air and water,
with the dryness of the air, and with the velocity of the wind,
and being usually greatest in summer and autumn. Thus supply
and loss are not balanced in detail; at somy seasons there is a
net gain and the lake surface rises, at others there is a net loss
and it falls, and the rise and fall together constitute an annual
oscillation.
A second difference depends on the variation of weather from
year to year. In some years more rain and snow fall, in others
less, and there is a similar fluctuation in the atmospheric con-
ditions affecting evaporation. When the rainfall is greater than
usual or the evaporation less, the lake rises ; when the rainfall is
small or the evaporation great, the lake falls. A succession of
wet years produces exceptionally high water, a succession of dry
years extremely low water. But there is a limit to such cumu-
lative effects, for when the lake is high its outflow is more rapid
than when it is low, and an automatic check is thus furnished.
Thirty years ago Colonel Charles Whittlesey compiled all
available data regarding the fluctuations of the lakes, and was
426
CHANGES OP LEVEL OF THE GREAT LAKES.
able to publish an account of the more important changes of the
lower lakes between the years 1838 and 1857, together with a
few data concerning exceptional phenomena in earlier years. In
1859 the United States engineers began systematic gauge-read-
ings, and their work is still continued. The following table is
based on their records, and shows the ordinary range of fluc-
tuations. Michigan and Huron are here treated as one lake
because their waters communicate freely through a strait.
Lake.
Superior
Michigan-Huron.
Erie
Ontario
Peri<Ml
of
record.
Usual date of
highest
Btage.
1871-87 lAugust.
1860-87 July or Aug. Jan. or Feb.j 1.2
lowest
stage.
April.
Mean
annual
range.
(Feet.)
1.3
June or July.
June.
l.«
1.8
Extreme range
for
whole period.
(Feet.)
3.0
3.9
3.5
4.7
ii ♦
The highest water known occurred in 1838, when Michigan-
Huron rose 26 inches above ordinary high stage, and Erie and
Ontario 18 inches. The lowest water known was in 1819, when
Erie fell about 3|- feet below its usual plane.
The present low water is the sequel of last summer's drouth.
The Signal-Service records indicated that the lake region received
in the year 1887 only about 26 inches of rainfall instead of its
usual quota of 33 inches. If the evaporation and the discharge
remained constant, the lakes should fall 7 inches by reason of the
defect of aqueous precipitation on their surfaces, and about as
much more by reason of the 'defect of inflow ; but, taking tlie
average for all the lakes, the actual fall from the low stage of
1887 to the low stage of 1888 has been only 7 inches. The
variation of rainfall was, therefore, great enough to account for
the variation of lake surface. That it was more than sufficient
is probably explained by the coolness of the autumn, which
tended to diminish evaporation. In Superior the low water of
last February reached 5 inches below the level of the average
low stage, a depression exceeded but twice in seventeen years.
«>«n»yy«iill ■ii ll.n^l i
jil'^^n
"m * y'
CHANGES OF LEVEL OF THE GREAT LAKES.
427
In 1879 and 1880 the wa'er was 3 inches lower. In Ontario, the
lake most affected, the low water of 1888 was 6 inches below the
average, but this record has been exceeded six times in the last
twenty-eight years. 1868 marks 10 inches below, 1872 16 inches,
1873 14 inches, 1875 (February) 13 inches, 1875 (December) 7
inches, and 1881 11 inches. In Michigan-Huron the recent low
water was but 2 inches below the average, and in Erie but one
inch. If our inland commerce has need to be assured of the
continued fidelity of its " unsubsidized ally," it can find comfort
in the contemplation of these figures.
The oscillations described affect an entire lake uniformly.
There are others that affect its parts differently, the water rising
."n one place while falling in another. The most powerful cause
of such displacement of level is the wind, which, driving the sur-
face water before it, heaps it up against the lee shore ; and the
greatest effects are seen in Erie, whose shallowness interferes
with the adjustment of levels by means of a return current
beneath. A gale blowing in the direction of the lake's length
has been known to raise the level seven or eight, feet at one end
and depress it an equal amount at the other.
Oscillations of a second kind are caused by inequalities and
variations of atmospheric pressure. When the air presses un-
equally on different parts of a lake an equilibrium is reached by
a depression of the water surface under the heavier column and
its elevation under the lighter. If the air pressures are ra{)-
idly shifted, as in the case of thunder-storms and tornadoes,
rhythmic undulations are produced analogous to those from the
dropping of a pebble in still water, and traveling like them to
remote shores. The rhythmic period is usually measured in
minutes and the height of the undulation in inches, but waves
of this class sometimes equal the largest* generated by wind.
The passage over Lake Michigan of a broad wave of barometric
change sets the water to swaying from side to side as we some-
times see it in a hand basin ; but the greater body has a longer
period, advancing and receding only eleven times in twenty-four
hours.
Third and last are the tides, which ebb and flow in lunar and
solar cycles as regularly here as on the ocean, but are unheeded
428
CHANGES OP LEVEL OP '^HE GREAT LAKES.
by the navigator. The highest determined spring tide rises
about 3 inches, and the average height of tide on the shores of
the larger lakes is probably not more than one inch.
And so these lakes of ours, that seem to ordinary observation
as enduring as the earth and yet as fickle as the weather, are to
the trained imagination of science both ephemeral and constant
l^ie geologisi, looks l)ackwar(l to the time when they were not,
and forward to the time when they will no longer be ; talks of
their birth, growth, decline, and death, and, comparing their
span of life with the *^arth's, declares them evanescent The
physical geographer, analyzing the motions of the water, refers
them to the attractions of celestial bodies, the pressures of air,
the friction of winds, the varying dryness of the atmosphere,
and the varying rain, and assigning each fluctuation to its appro-
priate cause, lays V)are a fundamental constancy to which the
navigator and the statesman may safely pin their faith.
G. K. Gilbert.
THB FORUM.
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