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Jacques W. (Jacques Wardlaw) Redway.

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they are confined to localities of comparatively small area.



IMPERFECT AND OBSTRUCTED DRAINAGE 173



But there are other lake-destroyiug agencies whose opera-
tions are carried on in ahnost every part of the earth ;
their manner may not be quite so apparent, but it is none
the less eilective. " Rivers are the mortal enemies of
lakes."* The stream that flows into a lake bears in its
volume more or less silt, which is promptly deposited in
the lake basin, lit-
tle bv little filling
it. With scarcely
an exception, at
the place where a
stream enters a
lake, either a del-
ta or a bar is
formed. This is
clearly illustrated
by the Volga, with
its mazy delta ;
by the St. Louis,
at the head of
Lake Superior ;

and by St. Clair River, at the head of Lake St. Clair, and
in the lakes of central New York.

The stream that flows out of the lake is equally destruc-
tive. It cuts away the rim of the basin, lowering the level
of the lake until the water is nearly or quite drained. Not
a few of the lakes that have disappeared from the earth
have been destroyed in this manner.

A diminution in the rainfall sooner or later will also
destroy a lak(!. The lakes and old lake-beds in the Great
Basin illustrate this fact. Formerly Great Salt Lake and
its scattered remnants — the latter, many of them, now dry
— covered an area almost half the size of Lake Superior.

♦ Gilbert.




LAKE ST. CL.^IR.

The mud flats at the head of the lake are the result of sedi-
mentation.



174



PHYSICAL GEOGRAPHY




LAKE BONNEVILLE AND ITS REMNANTS

The area in white shows the former si{e of the lake ; the small
lakes south of Sevier l^iver are practically dry.



At that time the
level of the lake
was nearly one
thousand feet
higher than at
present. After-
Avarcls, however,
the rainfall de-
creased and, the
indraught being
less than the
loss by evapor-
ation, the lake
dwindled to its
present size.

In almost
every part of
the world are
found old lake
shore-lines high
above the sur-
face whose level
they formerly
marked."^ In
some instances
they surround
the sites of
lakes that have
ceased to ex-
ist ; in others,
of lakes that are
reaching a pe-
riod of old age.
In any case



IMPERFECT AND OBSTRUCTED DRAIXAGE 175

they serve to demonstrate that hikes are very transit-
ory.

Many of the lakes of the United States have disap-
peared Avithin very recent times. Sevier Lake in Utah
has practically ceased to exist, and Tnlare Lake, California,
in twenty years has shrunk to less than half its former
size. The finger lakes of New York have lost a measur-
able part of their area in the past fifty years, and the level
of the Great Lakes has been materially lowered. In Lake
Erie the diminution has interfered so much with navi-
gation that a barrier across the outlet is now contem-
plated in order to raise the level of the lake.

Geographical Distribution of Lakes. — Lakes occur
in all parts of the earth, but they are by no means uni-
formly distributed ; as a matter of fact about ninety
per cent, of them are north of the 40th parallel of north
latitude.

\Vith respect to glacial lakes this law holds almost
universally true. The only exceptions are the few that
are found in the southern Andes and the snow-clad sum-
mits of high plateaus and mountains. Most of them
are situated in Europe and North America. In the lat-
ter division alone there are more than one hundred
thousand glacial lakes. Why are the latter of rare occur-
rence in the torrid zone ? AVhere in this zone would they
occur ?

Salt lakes are confined mainly to regions of deficient
rainfall.'' Why are they not common in regions of abun-
dant rainfall ? Most of them occair in the basin regions of
North America and Eurasia ; in the latter region there are
several thousand. The Caspian " Sea," the largest lake in
the woi'ld, is in this region ; its surface is eighty-four feet
below sea-level. Plava lakes are numerous in rej^ions
having a level surface and a light, periodic rainfall.



176



PHYSICAL GEOGRAPHY




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Most of the lakes may be
grouped in systems which
occupy lines of depression
on the earth's surface. Two
such systems are found in
the AVestern and three in the
Eastern Continent. The
lakes of the Western Conti-
nent are chiefly in North
America, and are embraced
mainly in two systems. The
largest and most important
is the belt stretching across
the northern part of North
America. An arc of a great
circle drawn from the city
of Bufialo to Point Barrow
passes through or near a
chain of lakes that includes
about the largest bodies of
fresh water in the world.
Find this chain on the map ;
describe the drainage and
character of the lakes. An-
other system extends from
the northern boundary of
the United States southward
through Mexico and the
Central American States.
Most of these are situated
in a basiu region ; describe
their drainage and character.
South America is remark-
able for the absence of lakes



IMPERFECT AND OBSTRUCTED DRAINAGE 177

in any considerable number. There are playa lakes along
the eastern base of the Andes, but the only lake of impor-
tance is Titicaca/^ a large body of water near the summit
of the Andes. Its surface is 13,000 feet above sea-level,
and it is the highest large lake in the world. Do its waters
reach the ocean ?

In the eastern continent a wide belt of lakes, situated
mainly between the 50th and GOtli parallels, extends across
Eurasia; what is their character? With resjject to lati-
tude their position corresponds pretty closely to that of
the glacial lakes of North America. These lakes constitute
the great majority in number, but they are of very little
importance.

A second belt follows the high mountain-ranges thas
stretch from west to east across the continent. It em
braces the playa lakes south of the Atlas Mountains ; the
glacial lake of the Alpine and Himalayan folds ; and the
multitude of playa and salt lakes in the basin region.
Many of the largest and most of the important lakes of the
continent are in this group. A third system in Africa
follows the line of the easte]-n highlands, and therefore,
unlike the other systems, extends north and south.
JSext to those of North America the African lakes are the
largest bodies of fresh water in the world. Name and. de-
scribe the four largest.

In one respect the Australian lakes are remarkable —
almost every one is either a playa or a salt lake. Not a
single one of any importance has an outlet to the sea.
What does this indicate with reference to the rainfall of
the continent ?

Swamps and Marshes. — In some places the drainage
waters cannot flow off, l)ut remain about even with the
surface, thereby forming what are variously termed
swamps, rnorassefi, pocosous, fxxjs, and marshes.^^



178 P11Y8I0AL GEOGRAPHY

Tuasmuch as almost every conditiou of imperfect or
embarrassed drainage results in marshy ground, it is evi-
dent that many different factors may bring about such
conditions. For instance, the surface of the land may be
so nearly a perfect level that the water cannot run off
until it has completely saturated the soil. Such instances
are very common : they occur in prairies and the flood
plains of rivers almost without number. They are com-
monly, thougli not always properly, called river terrace
swamps. Quite as frequently such morasses form at the
mouths of rivers, where they form delta sioamps, or estuary
sivamps.

In many instances the accumulation of vegetable matter
results in swamps. Under ordinary conditions the leaves
and twigs of forest growths quickly decay if they fall on
dry ground and, as a rule, the products of decay are
gaseous. Under such circumstances, therefore, no great
amount of solid matter results from such decay. But if
the ground be tolerably wet and rainfalls are frequent,
there may be enough moisture to prevent complete decay.
The vegetable matter gradually acquires a well-known
condition, in which it consists of a fine, black slime and a
mass of fibrous material called peat!^^ The accumulated
matter prevents drainage and a swamp finally results.
Most looodland sivamps are formed in this way.

Not all woodlands become swamps, however, for the
character of the vegetation nearly always has more or less
to do in swamp-making. Several species of sphagnum, a
kind of moss, are intimately connected with swamps. One
of these water-mosses consists of very long, thread-like
stems which, while dead at one end, are living and grow-
ing at the other. The dead portions do not decay, how-
ever ; they simply accumulate, packing tightly together
like an immense mass of sponge.



IMPERFECT AND OBSTRUCTED DRAINAGE 179

So, if the ground ever becomes wet enough for the
water-loving sphagnum to get possession, the area will
become a swamp, even if the accumulations of other vege-
table material would not result that wa}'. In time a
hollow, a pond, or even a marsh lake will be entirely filled




EFFECTS OF VEGETATION
Swamp vegetation beginning at the shore, are exleiuling oiitvards.

with the stems of sphagnum, thus forming ^jea^ hogs and
lacustt • ine si va mps. '^'^

If sphagnum once obtains in an area, an absolutely
level surface is not necessary for the formation of swamps.
The sphagnum will make its way up a slope of four or
five degrees and thus form a cJimhiiKj hog. Instances of
this kind are common in the Scandinavian Peninsula and
also in Nova Scotia and the New England States.



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EFFECTS OF VEGETATION

Swamp grasses and sphagnum have nearly filled the lake, and a quaking bog ts beginning

to form.

Sphagnous growths not only overuhchn shallow ])onds
and lak(;s, by filling their basins from top to bottom, but
sometinie;S they operate against d(!C])er waters. If the moss
stems cannot find lodgement at the bottom of the lake they
will rtoat at the surface, spreading, little by little, until the
surface is covered. TIk.' mat of sphagnum grows thicker



180 PHYSICAL GEOGRAPHY

aud broader, aud is made firmer by pasty matter, that
results from partial decomposition. lu time the surface
becomes firm enough to serve as the bed of a wagon road,
or even a railway. But the surface never gets quite firm,
and when one jumps upon it, or drives a wagon over it, the
shaking is always perceptible. In this manner a marsh
lake is changed to a quaking hog^^ or prairie tremhlanfe.

There are other species of vegetation ^^ that have more
or less to do with swamp formation — among them cane-
brakes. Canebrakes have long been associated with
swamps, but usually as a result. As a matter of fact,
canebrakes are not infrequently a cause of swamps. The
roots of the plant, spread out just below the surface of the
ground in much the same manner as does the sphagnum
above ground, making finally a mat that almost wholly
obstructs drainage.

Coast or salt marshes are confined to low coast plains.
They are destitute of water mosses, but they contain other
species of vegetation that are quite as effective. The first
step in the formation of a salt marsh is an area of shallow,
still water. Usually this results as soon as a sand-bar is
thrown across a cove or estuary. Waves prevent the
development of marine swamp, but in throMdng up a bar
they make the condition that is a foundation for the
swamp. In a few instances sheltering headlands keep the
water still enough for the growth of marine plants.

The next stage is the growth of eel grass, a plant with a
long, slender blade. This takes root as soon as the cove
l^egins to fill with sediment ; it grows rapidly, and the
half-decayed remains contribute not a little in filling up
the marsh. But eel grass grows only when covered with
salt water, and when the decayed vegetation, mixed with
wind-blown rock waste, has filled the cove to low-tide
level, it perishes. After a time the marsh passes a step



IMPERFECT AND OBSTRUCTED DRAINAGE 181

higher in its formation, receiving layer after layer of sedi-
ment that build its surface to a level Avliere it is awash at
high tide only.

By this time true salt-marsh grasses, reeds, rushes, and
tules obtain possession. These species thrive only when
their roots are covered with salt water at short intervals.
They accumulate until the level of the marsh is built
above the level of the highest tides. When this stage is
reached turf grasses gradually take the place of salt-marsh
grasses, and the marsh becomes meadow land.

Another plant active in swamp-making is the mangrove-
tree. This tree thrives only in salt water. It propagates
itself partly by upshoots from the enormous mass of roots
that trail under water, and partly by seeds. The growth
and spreading of mangrove roots and trunks is so great
that coast outlines are extended rapidly and fringing bur-
riers are formed as well. In Florida mangroves and corals
are yearly adding measurably to the swamp-land surface
of the State.

The tundras of the Arctic coast plain furnish an inter-
esting example of the combined action of ice, fresh water,
salt water, and moss. These shores are almost constantly
covered with ice. Not only are they inundated by tidal
waters, but also by stream waters. The mouths of the
streams are frozen, and the flood water, finding its chan-
nels blocked with ice, spreads broadcast over the surface.

During flood seasons the stream waters are filled with
sediment, and this is spread over the plain. Moreover, it
furnishes suflicient nutriment to heavy growths of coarse
moss, and the latter, in turn, not only holds the sediment
in place, but it also in no small degree prevents the melt-
ing of the ice. As a result, this plain is a perpetually half-
frozen morass, and probably the most inhospitable region
on the face of the earth.



182 PHYSICAL GEOGRArHY

Physiographic Aspects of Marshes. — Notwithstand-
ing the fact tliat the urea of marshes and swamp is com-
paratively smaU, it is probable that much of the land sur-
face of the earth has been a marsh or a swamp in some
period of its existence. In a way marine marshes may be
considered as land at an intermediate stage between sub-
mergence and elevation. Hence, volcanic areas excepted,
the shallow lagoon, the eel grass swamp, the barren mud
flat, the salt grass marsh, and the turf-covered plain is
each, in turn, an incident in the final elevation of a body of
land above sea-level.

Along the coast of the South Atlantic States one may
find the lagoons and the eel grass swamps ; along the
shores of the Gulf there are, in addition, very broad mud-
flats ;'^^ in the bay of San Francisco and the adjacent
waters are many square miles of salt-grass and tule
marshes ; and almost everywhere beyond the reach of tidal
waters there are the turf- covered plains.

The range of fresh-Avater swamps may not be quite so
great, but economically they are quite as important as the
marine marshes. Their evolution and physiography,
moreover, is rather more complex than the development
of marine marshes, but in two respects they are alike — •
namely, vegetation makes them and, in the long run, it de-
stroys them.

Vegetation may, and usually does, operate to create
swampy conditions, but the process of destruction does
not differ from that of creation. The accumulation pro-
ceeds until the surface is lifted to a level where the ground
waters may flow off.

Cultivation destroys swamps, and the process of destruc-
tion is simple. Most grains and food-stuffs require a com-
paratively dry soil, and the very act of ploughing creates
drainage channels in which the water flows off. Where



IMPERFECT AND OBSTRUCTED DRAINAGE 183

ploughing lias not been sufficient, ditching and under-
draining accomplish the same results.

But swamps themselves exert not a little influence on
vegetation and its distribiition. Many species of tree and
shrub that thrive in moist or dry soils perish if the soil be
saturated. Thus, a swamp once obtaining in a woodland
area, it is a question of time only before many, possibly
all of the forest species disappear. In almost every fresh-
water swamp the most marked features are the stumps
and trunks of dead trees — a result of the development of
swampy conditions. What species of evergreen thrives in
swampy lands ?

Economic Value of Swamps. — SAvamp, marshes, and
bogs, although practically uninhabitable for human beings,
have had a very far-reaching efi'ect in the development of
civilization. In evidence of this the results of the coal-beds
may be cited. The enormous development of commerce
and manufactures is due almost wholly to the coal-fields of
the world, and these almost without exception are the
swamps and marshes of prior geological ages.

The swamps of the present time are the most productive
areas to be drawn upon in the future. The soil possesses
great depth, and its nutrient qualities are exceedingly
great. Swampland crops themselves are of no little im-
portance, and the rice-swamps probably supply food to a
greater number of people than all the other grain-fields in
the world. Incidentally, the world's supply of cranberries
comes mainly from swamps, and the peat-bogs furnish fuel
to not far from fifty millions of people.

The Movement of Rock Waste. — In this and the
preceding chapters it has been shown that the higher parts
of the land are almost everywhere crumbling and wasting
away under the action of water in one or another of its
different forms. Rain, snow, ice, running sti'eams, and



184 PHYSICAL GEOGRAPHY

even the winds are factors that are unceasingly active, and
their legitimate work is to wear away the land and trans-
port the material removed to sea-level.

On the steeper slopes, as a rule, the rock waste is coarse,
the fragments sometimes weighing many tons. On its
way downward it is broken and worn in various ways
until, at sea-level, it is very fine. Much of it is also min-
gled with the remains of vegetation, and takes the charac-
ter called soil.

The soil is deposited in river valleys in the form of flood
plains, delta plains, estuary plains, and coast plains. Re-
view briefly the formation of each. Some of it is arrested
by obstructions along its downward journey and, filling the
depressions in front of the barriers, forms lacustrine plains.
Name several examples. Explain how all these physio-
graphic processes aflfect the habitability of a region.

The ivaste of the old land is the material of the neiv.

QUESTIONS AND EXERCISES— Study any lake or pond near
which you live and classify it as marsh, glacial, swamp hole, or salt ;
make a map of it.

Note whether a coast plain is present, or whether the water-level is
at the foot of cliffs or banks.

If there is a fringe or belt of coast plain what does it indicate con-
cerning the present and the former size of the lake ?

Note whether or not the border is marshy and thickly covered with
vegetation, or whether it is strewn with large bowlders.

In what, if any, part are the waters muddy ? From this determina-
tion endeavor to find where the sediment is chiefly deposited.

From the foregoing write a description of the body of water.

From the diagram of the Great Lakes, together with a good map,
p. 176, prepare a description of these lakes. What will be the effect
of the recently completed ship canal at Chicago, on the level of Lake
Michigan ?

What would be the effect on the character of the water were the
basin of the Caspian Sea to fill until it overflowed ?

If the basin of the Black Sea were elevated twenty or thirty feet
what would the water be, salt or fresh ?



IMPERFECT AND OBSTRUCTED DRAINAGE 185

Mention some of the benefits resulting from the Great Lakes of North
America, with reference to commerce, industries, and climate.

Which of the two Great Lakes may be regarded as a single body of
water? Why?

The level reach of land in the illustration, p. 171, was formerly a
lake ; explain how it became the flood plain of a mountain stream.

From any convenient source of reference write a description of Death
Valley, California, or of the Dead Sea, Syria.

From the section of the marsh lakes, p. 166, prepare a description
of them, concerning their depth, altitude, and navigability.

COLLATERAL READING AND REFERENCE.

Russell. — Lakes of Nevada, Physiography of the United States,
pp. 101-130.

Le CONTB.— Elements of Geology, pp. 80-82, 580-581.
Shaxer. — U. S. Geol. Survey, An. Rep't, 1800.

NOTES

' There is no distinction between a lake and a pond, except the
very indefinite one of size.

' Lakes are sometimes formed, however, in places where a steep
slope joins one that is very moderate. Examples of such lakes
occur in the eastern slope of the Scandinavian Peninsula and in
Nevada.

= Marsh lakes are rarely more than a few feet in depth. They
are seldom navigable, and connnercially they are of but little
importance. In Europe many such lakes have been drained in
order to make cultivable land of their beds. There are several
instances where such basins are filled with water and used for fish
culture for a period of several years, and then drained and culti-
vated for a like period.

* Occasionally lakes are formed on mountain-slopes by the
agency of landslips, but they are seldom long lived. Sometimes
they break through the material that blocks their overflow, but
more commonly the outflowing water cuts a channel through it
deep enough to drain the lake to the bottom.

'"Walled" lakes are common in Iowa, Minnesota, and Da-
kota. So regular are the walls of their shores that for many



186 PHYSICAL GEOGRAPHY

years it was commonly believed they were artificial and were
built by a prehistoric race of people. As a matter of fact, how-
ever, tiie walls are the work of ice. In severe winters these lakes
freeze nearly to the bottom ; but inasmuch as water increases in
bulk when it freezes, the ice, in expanding, pushed the bowlders
shoreward. Time and time again this process was repeated until
the rocks were pushed back to a position where the resistance of
the earth back of them was equal to the pushing force of the ice.

" In scraping out these basins not the ice itself, but the frag-
ments of rock held at the bottom, form the cutting tool.

^ There are several instances in which flowing lava has blocked
up a river channel and formed a lake. In at least two places the
Columbia River was thus blocked, and the high-water marks of
the lakes formed are still plainly visible. In each instance, how-
ever, the river succeeded in recovering its channel and the lakes
were therefore drained. Accidental lakes, resulting from the
blocking of a river channel by coulees of lava, are common in
volcanic countries. Still another accidental lake is the crater
lake, which is merely an old volcanic crater filled with water.
Crater Lake, in Oregon, and Lucrine Lake, in Italy, are exam-
ples of such lakes. The former is about 2,300 feet deep and is
a wonderfully interesting body of water.

*• Not only have coves of the sea-shore been shut off by bars,
thus forming lagoons, but the same process has been carried on
along the shores of lakes. Such lagoons are in process of
formation at the head of Lake Superior, Lake Erie, and Lake
Ontario. In each case, however, the formation of the lagoon is
not yet complete, owing to the fact that the current from the
river is still able to keep a channel open.

" Albemarle and Pamlico Sounds are examples, and they re-
main as sounds for the reason given in the preceding note. In
other words the sound is often an intermediate stage between a
bay and a lagoon.

'" There are a few small salt lakes having outlets, but none of
importance. They are saline because of salt springs within their
basins. Not all so-called salt lakes contain common salt, how-
ever ; in many various alkaline substances are found.

" Near the City of Mexico formerly there were several lakes that
overflowed into a fourth. The latter is salt, the others not drained
are fresh. Utah Lake overflows into Great Salt Lake through



IMPERFECT AND OBSTRUCTED DRAINAGE 187

Jordan River ; its waters are fresh. Lake Chad, in Africa, is
normally without an outlet. Occasionally, however, in seasons
of unusual rains, it overflows into the Libyan Desert. This
occasional ovei'flow is sufficient to keep its w'aters fresh. The
waters of the Caspian Sea are kept moderately fresh by a similar
process. On its eastern border is a gulf, the Karabogas, con-
nected with the main body of the lake by a narrow strait. The
waters of the gulf are very shallow, and so great is tiie evapora-


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Online LibraryJacques W. (Jacques Wardlaw) RedwayElementary physical geography : an outline of physiography → online text (page 12 of 25)