Geomorphology – NJCU GEOS 335
Lec 1 – Easterbrook Chap 1 (Intro) & Chap 2 (Basic Concepts)
Chap 1 – Introduction to Geomorphology
Defined: “study of origin and evolution of topographic features by physical & chemical
processes operating at or near the earth’s surface”
Geomorph interdisciplinary, overlaps with:
 Hydrology
 Glaciology
 Geography
 Statistics
 Climatology
 Soil science
 Aerodynamics (!)
Historic contributions:
Geomorph starts in 5th century BC –
- Herodotus (ca. 450 BC) recognizes Egyptian rx with marine fossils formed beneath
the sea; he also suggested that Nile R delta took 1000s of years to form (far ahead
of his time in this type of thinking)
- Aristotle (ca. 350 BC) recognizes that streams can erode, and also deposit alluvium
- Lucretias (ca. 100 BC) recognizes decay of rx by weathering
- Strabo (ca. 0 AD) suggests principles of delta growth
Dark Ages – not much happens in geomorph, except
- Avicenna (ca. 1000 AD) suggests that mts can be created by crustal upheaval and
then sculpted into features by erosion (landscapes carved by erosion after upheaval
is a key geomorph concept)
Renaissance – things pick up again
- Da Vinci (ca 1500) sees marine fossils in rocks, sees streams sculpting landscapes
- Steno (ca 1650) sees that running water is the chief agent of erosion
Despite the lack of progress because of the Church’s insistence upon instantaneous
creation of earth (literal reading of Genesis), there was some progress also made in
18th century:
- Targioni sees that streams erode differentially depending upon rock type they run
through
- Leclerc sees potential for peneplanation (creation of a completely flat surface) by
stream erosion
- Guettard sees destruction of cliffs (chalk, poss White cliffs of Dover) by wave action
- Desmarest presented theory that landscapes evolve through successive erosional
stages
- DeSaussure recognized erosion & deposition caused by glaciers.
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Father of modern geology, James Hutton (1726-97) fought against “Neptunists” (people
who thought that Noah’s flood receding flood waters caused most deposition of rx and
subsequent erosion as flood waters receded) and the “catastrophists” (people who
thought that Earth features formed very quickly by catastrophic events since God
created the world ca 3000 BC according to Bishop Ussher), by preaching the idea of
“uniformitarianism”, a cornerstone of modern geologic theory (leads us to be able to
say….“The present is the key to the past”….)
Playfair (1802) and Lyell (“Principles of Geology” published from 1833 to 1875)
continued in the footsteps of Hutton, with clearer writing styles that led to more
widespread reading and greater public acceptance of modern ideas.
Others in 19th century also made important contributions:
- Surrell (ca 1850) spelled out erosional & depositional parts of streams along the
longitudinal profile
- Reade (ca 1900) proved that solution of rx (ie, dissolving of limestone) was
important in erosion.
- Leslie (ca 1900) explained explained differential erosion of Appalachians
- Geikie (ca 1900) studied relative “erosiveness” of marine vs subaerial (land-based)
processes, concluded that the latter is more effective because it acts upon the entire
uplifted surface of a continent, whereas marine processes act only on the shoreline
(…this is not entirely true, but it is fair to say that much more erosion occurs on land
than in the ocean, where the lion’s share of the processes are depositional, not
erosional
 European glaciology really was the trigger that kicked off modern geomorphology
- Bernardi (ca 1825) publishes first evidence of earlier glaciation (in area of N.
Germany now free of ice)
- Agassiz (1840), very famous glaciologist, popularizes the concept of glaciers
formerly covering much larger areas of N. Hemi, travels to N. America, spreads
glacial concepts here too.
- TC Chamberlin & Frank Leverett (ca 1900) documented the existence of a major
continental glacier that originated in Canada and expanded south many 100s of
miles into U.S.
Even Darwin contributed to geomorph, by observing the immediate uplift if several feet
in elevation (and subsequent erosion) of the Chilean shoreline after an 1835 eqk
In last half of 19th century, some American pioneers were also geologists:
-
-
John Wesley Powell traveled through the Grand Canyon on the Colorado R., came
up with the concept of “base level” of rivers (base level is sea level, ultimately). As
streams drop closer to base level, gradients (longitudinal slope) are reduced and
they lose ability to erode (and start depositing the sediment they have been carrying
Grove Karl Gilbert (“the present is the key to the past”) followed in Powell’s footstep,
with work in Henry Mts of Utah documenting stream erosion and quantifying the
relationship between stream load, discharge, velocity, and gradient.
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In 20th century, W.M. Davis combined much earlier work to form the concept of “cycle of
erosion”:
Surfaces become dissected by erosion, and stream-carved landscapes evolve to a final
stage of a planar surface (“peneplain”) near base level. Stages are
Youth
Maturity
Old age
On to Chap Two…
Basic Concepts
Check out photo on p.7 ! Multiple meander belts of the same river, sweeping back and
forth, reworking sediments
I.
Fundamental Principles – need to understand both modern surface processes
(and the controlling physics and chemistry of those processes) and historic
influence of geologic time. Key is understanding which processes are at work,
for how long, on what materials. With training (and luck), you can identify the
appropriate stage of geomorphic evolution (youth, maturity, old age) of geologic
features
a. Geomorphic process – each process bestows distinctive feature(s) upon a
landscape…characteristic “assemblages of landforms” develop. You should
be able to unravel, from the landform itself, the original feature (if any) and
the geomorphic process that modified that feature.
Simple example…. A mountain valley between two peaks starts out looking like:
River
…then becomes modified to look like this:
What happened??
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Look at the initial form, with a stream running through it. Imagine what would happen if a
large alpine glacier came down the stream valley, plucking rocks as it went?
Ice
A classic “U-shaped valley” is what is carved and left behind once the ice melts
Surface processes responsible for most of the earths’ features are:
 Weathering
 Mass wasting (land- and mudslides, earthflows, rockfalls, soil creep)
 Running water (streams, rivers)
 Groundwater (chemistry dissolves rx in one place, precipitates them in
another place)
 Glaciers
 Wind
 Waves
 Wind
 Tectonism - earthquakes cause fault movement, one block uplifted (or
downthrown) relative to another
 Volcanism
b. Evolution of landforms – landforms evolve continuously, through a sequence
of forms.
c. Geologic structure – tectonic disturbance of the crust can create landforms,
either by the actual disturbance, or the secondary differential erosion of diff
rx. MOST of Earth’s major, large-scale features like mountains and ocean
basins, are result of large-scale tectonic motion.
BEFORE:
There are more localized geomorphic features known as escarpments, or
fault scarps, that are the surface expressions of individual faults..they
directly offset the land surface:
AFTER:
fault scarp
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In addition to these neotectonic features, there are longer-term surface irregularities
caused by differential erosion:
Before:
After:
Lmstone
shale
shale eroded away
Limestone
left
this is how the Appalachian Valley and Ridge have been formed.
Extra Credit: look up the Valley and Ridge, find a representative cross-section showing
the subsurface geology and the present-day land surface
d. Geomorphic systems- to understand surface processes and geomorphic
systems, one needs to understand:
 Uniformitarianism – understanding of relict landforms created by ancient
processes can be understood if those ancient processes are similar to
those operating today (which they more or less are…). So the key is to
extrapolate backward in time, and visualize how things may have
developed.
 Equilibrium systems – aka “negative feedback” – a balance between
opposing forces - GK Gilbert (in the 1870s!) came up with concept of
“graded” stream – one that is in equilibrium with surroundings and neither
erodes or deposits sediment (p.9 detailed explanation):
If slope is steeper than that required to maintain velocity needed to
carry the sed load, erosion will occur until bed is lowered and
velocity drops

II.
Positive feedback – in this case the change is in the same direction as the
forcing mechanism. Their example is a meander bend in a river. The
bend progressively moves outward, ultimately intersects with another
bend. Good quote: “positive feedback systems carry the source of their
own destruction and eventually accelerate to self-elimination.
Rational & empirical approaches – need both to fully understand systems
a. Rational approach focuses upon determining cause-and-effect relationships.
b. Empirical approach focuses upon characterizing the nature (often
quantitative) of the relationships.
c. Multiple working hypotheses – a cornerstone of modern geology (keep an
open mind, always consider multiple ways to explain your observations).
Steps:
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Observe facts
Develop multiple hypotheses
Test hypotheses (reject those that you can, come up with new ways
to test validity of the survivors)
Not always possible to narrow down things to just one alternative
Example – use Fig 2-2 on p. 11-12 to focus on valley North of Cedar Creek. Several
anomalies, and a question: How did this valley form?
Steps:
ID all possible alternatives for origin of this valley (present configuration in 2-2a):

Pond Creek (currently flowing NW) probably too small to have formed the
valley

Same likely true for small S-flowing stream

The possible candidates that eroded this valley are:
1. Kentucky R
2. Cedar Creek
 One has a hard time trying to envisage the Kentucky R originally cutting the
channel and then jumping to it’s present course, so the Kentucky R as a
source is probably out
 This leaves Cedar Creek, and if you imagine Fig 2-2B, it is not hard to see
that Cedar creek could have flowed from SE to NW at some point in the past,
dumping into Kentucky R.
 Later, it is conceivable that Cedar Crk could have eroded a meander bend
into the Kentucky on it’s outside edge, which would have caused an
immediate switch of Cedar Crk drainage into the Kentucky
So the most likely hypothesis to explain the development of this valley is the last one.
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