CAUSE
AND EFFECT:
Aspects
of the geomorphology debate
David J. Tyler
Geologists have always
had a reputation for plain speaking - a characteristic which partly explains
the intensity of some of the debates that have taken place over the years.
Henry De la Beche, the Founder and first Director of the British Geological
Survey (1796-1855) provided an additional weapon in the armoury of debate:
the satirical cartoon. De la Beche belonged to the catastrophist school of
geology and many of his cartoons were directed against the uniformitarian
geologists, led by Charles Lyell.
| Recently,
a long lost cartoon entitled "Cause and Effect" has been recovered
(redrawn opposite). In a letter to Nature, Haile (1997) republished the
cartoon and commented in its significance. It was found among the papers
of William Buckland, first Professor of Geology at Oxford, in the archives
of the University Museum. |
 |
The cartoon portrays a
familiar experience for parents who have taken their toddler out for a walk.
The young boy (thought to be Frank Buckland, the eldest son of William Buckland)
is standing beside his nurse on some high ground and urinating. The nurse
realises that the trickle becomes a stream which in turn flows down a huge
valley. The nurse exclaims: "Bless the baby! What a walley he have
a-made!!!" Haile (1997) comments:
"This
was intended as an ironic comment on the uniformitarian outlook of Charles
Lyell (a former pupil of Buckland, and Darwin's geological mentor), who championed
the idea (now accepted for most valleys) that slow-acting erosion by rivers
has formed the valleys they occupy, as opposed to pre-formation by earthquakes,
faults, catastrophic floods or marine action). One of the objections to this
so-called fluviatile theory was provided by `mis-fit' streams - huge valleys
occupied by small rivers that it would seem could not have excavated them,
even given an immense period of time. This is the type of stream that De
la Beche illustrates."
One colleague (also a
catastrophist) who was delighted by the cartoon was Roderick Murchison (who
succeeded De la Beche in leading the Geological Survey). Murchison was a
little concerned by the appearance of a new book by De la Beche, The Geological
Observer, which seemed to give some ground to the uniformitarians. He wrote
in 1851:
"I
could only have wished that it did not seem to me that you favoured the `piddling'
school more than of old, when you drew Frank Buckland as a baby denuding a
valley. We shall hear a good deal more of the book tomorrow night; so I reserve
my say except to hope that you have not actually become an inch by inch geologist"
(cited by Haile, 1997).
However, catastrophism
was on the way out: soon the glacial theory of Agassiz explained many puzzles
and the sculpting action of glaciers provided the inch-by-inch explanation
of `mis-fit' valleys. This resulted in the triumph of uniformitarianism.
With hindsight, it can
be argued that it was a triumph of dogma rather than of empirical science.
Whilst some valleys can be explained by the action of glaciers, this mechanism
is not applicable to many parts of the world where no one suggests glacial
activity. Research by Drury (1965) reached the conclusion that there is a
continuing problem of explaining mis-fit streams. Quantitative analysis suggests
that streams have had in the past a discharge rate some 20-60 times their
present rates. This has yet to be satisfactorily incorporated into current
models of landscape formation.
Many popular books appear
to say that the problems are all resolved. However, what is often presented
as well-attested fact is something which is essentially theoretical interpretation
which emerged at the turn of the 20th Century. This is the model of geomorphological
change developed by W.M. Davis, known as the geographical cycle. When scrutinised
in the light of hard geomorphological data, the Davisian cycle has not been
found to be adequate. In the mid 20s, the first major alternative was launched:
the Treppen concept of Walther Penck. This was picked up and developed by
King in the 1950s. Garner (1974) gives a helpful overview of these concepts
and notes that theoretical change continues:
"In
the wake of recent discoveries in geotectonics, the diastrophic basis for
the theoretical frameworks of Davis, Penck, and King is thrown into serious
question... (p.32)"
Garner believes that all
these earlier theories underplayed the role of climate, being too entrenched
in Huttonian-type uniformitarianism. He says:
"... the present
is like the past as a man is like an amoeba; there is a relationship, one
whose understanding requires a knowledge of many developmental stages and
a unifying theory (p.39)."
Earlier
models of geomorphological change were too committed to environmental equilibrium.
"The
extent to which environmental disequilibrium characterises the earth cannot
be easily expressed. It is pervasive. Yet it is probably normal. And the
dynamic equilibrium state is therefore comparatively rare. Paradoxically,
therefore, "the key to the past" which was formulated to counteract
"catastrophism" is a highly dynamic earth with changes which are
intermittently catastrophic, frequently accelerated by disequilibrium, and
possibly not too effective where they are truly gradual." (p.39).
So, too often a dated
theoretical framework is imposed on to the field data - and this is having
the effect of locking people into long time frames for geomorphological change.
One geologist stated to me that: "There is a literal world of evidence
for the geographical cycle" - but Garner points out the many deficiencies
in Chapter 1 of his textbook. It is time to move on from the straight-jacket
which Huttonian thinking has brought to geology.
There are welcome signs that geologists
are moving on. A major review paper by Orme (2002) documents the impact of
paradigms in geomorphology. For many years, he writes, the discipline was
dominated by the Davisian cycle of erosion (Davis, 1899), a child of uniformitarianism.
According to Orme:
“It assumed
rapid uplift followed by prolonged structural quiescence during which geomorphic
processes, assumed rather than measured, denuded the landscape over a time
interval that was equated with life in terms of youth, maturity, and old age.
This was an evolutionary model that placed emphasis on inevitable, continuous,
and irreversible processes of change through time although, over time, a new
cycle could be initiated by renewed structural uplift or climate change. If
one accepted the basic premise, the Davisian model was alarmingly simple,
couched in terms which most students could readily understand.”
He continues:
the foundations of this theory were never properly tested, but it had a remarkable
impact on successive generations of geomorphologists. In more recent times,
there is a much greater openness to mobilistic theories. The human face of
science is apparent in both the proposers of new theories and in the reception
given to them.
“New
ideas are often opposed by establishment conservatism, language barriers,
the perceived surrealism of new concepts, and simple ignorance. In contrast,
new ideas may be accepted, sooner or later, by virtue of simplicity, forceful
and well-connected leadership, or the death of opponents. Although mitigated
by the information revolution of recent decades, these forces still persist
and influence the extension of new ideas into a larger arena.” (Orme, 2002)
Bloom (2002) states boldly: “Only
a few very young landforms are the result of currently operating geomorphic
processes.” Much is in the melting pot of ideas, and much new thinking is
non-uniformitarian and tectonically driven.
The classic breakthrough for this
paradigm change concerns the Channelled Scablands. These features were formed
by several catastrophic drainings of Lake Missoula during the Pleistocene.
One geologist, in a personal communication, described it as follows:
"The
canyons are cut straight, not meandering, the land looks like it has been
flooded and intensely scoured. There is very little substantial vegetation,
as in practically no trees, mostly sagebrush. There are giant ripple marks
along the course of the flood. These have a wave height of approximately
10 feet and a wavelength of about 100 yards. These are very rare topographic
features explainable only in a catastrophic scenario."
What is interesting is
that these features which today are "explainable only in a catastrophic
scenario" were once regarded otherwise. For 50 years, J Harlen Bretz
was a lone voice in American geology in defending the catastrophic origin
of these features. Eventually the tide of opinion turned, and Bretz received
a telegram from the International Association of Quaternary Research saying:
"We are now all catastrophists" (Bretz 1969, Gould 1983, Ager 1993a,
Ager 1993b). Why were Bretz' colleagues so blind to the evidences: the answer
is - they were locked into the wrong interpretative framework.
Ongoing geomorphological
research may be seen as providing further contrasts between the present and
the past. For example, consider the 1993 flood of the Upper Mississippi River,
which is classified as an "extreme flood". The peak discharge rates
put it into the 100-yr flood or the 500-yr flood category, depending on which
method of analysis is used. The surprising thing about this flood was that
it left little or no substantive evidence of its occurrence! Magilligan et
al. (1998) concluded that "little sediment was available for transport
during the summer 1993 flood", and that there are conditions where "a
large flood might be expected to leave little lasting geomorphological evidence
of its passage". Compare this with some rock strata displaying clear
evidences river channels with overbank deposits: such as in the Middle Jurassic
of the Yorkshire Coast (Tyler, 1994). These deposits formed so quickly that
there was no time for significant vegetation to grow - although there are
evidences of drying out of the surface, with desiccation cracks and dinosaur
footprints.
As a further example,
consider the glacial mega-flood emerging from the Vatnajokull glacier in Iceland
initiated on 5 November 1996. This was the largest volcanically-induced flood
that has occurred in living memory: volcanic activity below the glacier led
to an estimated 4 km3 meltwater. This water found a path under
the ice and eventually emerged with catastrophic consequences from the Skeidararjokull
glacier on the south side of the ice sheet. Whilst the flood waters carried
enormous quantities of sedimentary material, the damage to road, bridges and
power lines was thought to be largely due to collisions between mobile ice
blocks and fixed structures. Worsley (1997) has documented the main features
of the event and commented:
"Advocates
of the importance of catastrophism in geology need search no further than
Iceland for supporting evidence as clearly episodic catastrophism is clearly
an integral component of the processes fashioning this landscape."
How far this mega-flood
provides an analogy for landscape-forming processes is a matter of debate.
However, the key point noted here is that catastrophic flows of this extreme
character do seem far more appropriate for carrying sediments and to depositing
them as the stratified beds we see in the rock record.
Conclusions:
De la Beche's cartoon
identifies a continuing problem for earth scientists. Are present-day processes
sufficient to account for the deposits and structures observed in the rock
record? Appeal to glacial action provided only a partial response to De la
Beche (although it was regarded as a full response at the time). The forces
mounding the surface of our planet appear to be orders of magnitude greater
than those forces to which we are accustomed. Such forces are necessarily
catastrophic - and must necessarily operate over short timescales. Christians
who hold to the historicity and trustworthiness of Noah's Flood and the Book
of Genesis have a key which helps to unlock the door of understanding regarding
Earth's catastrophic past.
References
Ager,
D.V. 1993a, The nature of the stratigraphical record, (3rd edition),
John Wiley & Sons Ltd., Chichester.
Ager,
D. 1993b, The new catastrophism, Cambridge University Press, Cambridge.
Bretz,
J H. 1969, The Lake Missoula floods and the Channelled Scablands, Journal
of Geology, 77, 505-543.
Bloom A.L.
2002, Teaching about relict, no-analog landscapes, Geomorphology, 47(2),
303-311.
Davis, W.M.
1899. The geographical cycle. Geographical Journal, 14, 481-504.
Drury,
G.H., 1965, Theoretical implications of underfit streams, USGS Professional
Paper 452-C, C1-C43.
Garner,
H.F. 1974, The origin of landscapes, Oxford University Press, New
York.
Gould,
S.J. 1983, [to be supplied]
Haile,
N.S. 1997, The `piddling school' of geology, Nature, 387(12
June), 650.
Magilligan, F.J., Phillips,
J.D., James, L.A. and Gomez, B. 1998, Geomorphic and sedimentological controls
on the effectiveness of an extreme flood, Journal of Geology, 106(1),
87-95.
Orme A.R.
2002. Shifting paradigms in geomorphology: the fate of research ideas in an
educational context. Geomorphology, 47(2), 325-342.
Tyler, D.J. 1994. Tectonic
controls on sedimentation in rocks from the Jurassic series (Yorkshire, England).
In Walsh, R.E. (Ed): Proceedings of the Third International Conference
on Creationism, Creation Science Fellowship, Inc., Pittsburgh, PA.
Worsley, P. 1997, The
1996 volcanically induced glacial mega-flood in Iceland - cause and consequence.
Geology Today, 13(6), 222-227.
First drafted 1998
Updated May 2004
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