>and
>> then finally it must account for why the erosion of the canyon took place on
>> a topographic high. The Colorado plateau was slowly uplifed (domed) and the
>> river cut into it as it was uplifted. Since rivers avoid topographic highs,
>> like this, any catastrophic erosional waters (as is envisioned by Steve
>> Austin) would not run across the top of the hill. The water would flow
>> around the hill, meaning that the Grand Canyon should not be where it is,
>> but rather on the edges of the uplift.
>
>It is obvious from this that you have not read the breached dam proposal
>by Austin and others. The theory that the plateau was slowly uplifted
>as the river cut through it has been proved wrong ages ago, when they
>found the muddy creek formation. The most current theories have no
>evidence and evidence.
Recently my friend and new associate pastor loaned me his copy of Steve
Austin's video on Mt. St. Helens and asked what I, as a geologist,
thought of it. Part of that video discussed the breached dam proposal
for the Grand Canyon as put forth by Austin and others. In my reply, I
related the results of a literature search on the "current theories" of
Grand Canyon formation. Since these current theories are somewhat
different than those described above, I thought that I would toss my
previously formatted notes into the fray!
______________________________________
Grand Canyon Erosion: My comments follow a summary of Austin's ideas.
Austin uses this newly formed Toutle River "canyon" at Mt. St. Helens
as a model to explore his catastrophic interpretation of the
formation of the Grand Canyon. First he makes some provocative
statements like:
"Most geologists who know about the geology of northern Arizona
have junked the idea that the Colorado River cut the Grand
Canyon."
and,
"Textbooks tell us that the Colorado River cut the Grand Canyon but
the geologists who really know about it have given up that idea."
Austin then asks, "What caused the Grand Canyon?". He points out
that the Canyon cuts the upwarped Kaibab Plateau and tells us that
this is an "incredible problem." Austin then implies that the modern
interpretation of Grand Canyon formation supports his flood
catastrophism. He tells us that many geologists suspect that this
was some sort of enormous breached dam - that there was some sort of
rapid catastrophic breaching event from lakes perhaps to the north
and east of the Grand Canyon. In conclusion he states:
"Much like mud came down out of Mt. St. Helens, water over-topped
the dam. We have a broken dam. We might be looking at the
spillway erosion from this catastrophically drained lake or series
of lakes."
----------------------
{Grand Canyon story} Now I don't consider myself an expert on
northern Arizona geology and so I went to the literature to find out
what those "geologists who know about the geology of northern
Arizona" are saying. The most recent comprehensive summary on the
Grand Canyon that I found is by Ivo Lucchitta (1989, History of the
Grand Canyon and of the Colorado River in Arizona; _in_ Jenney, J.P.
and Reynolds, S.J., editors, Geologic evolution of Arizona, Arizona
Geological Society Digest 17, p. 701-715. Note: This AZ GS Digest
volume is already considered such a classic that the USGS library
here in Denver stores its copy in their rare book collection for safe
keeping!). Although this article is too recent to have been included
in Austin's first Mt. St. Helens vs. Grand Canyon presentations, it
certainly is old enough that it should have contributed to his 1993
film version.
When Austin says that geologists don't believe that the Grand Canyon
was cut by the Colorado River, he is giving his listeners a partial
truth but also implying that the only real solution is catastrophism.
Listen to the words of Lucchitta and see if you think that Austin
has really represented what "geologists who know about the geology of
northern Arizona" are saying. (I apologize for the length of the
following quotes but I think it is important to get the flavor of the
argument. Information, translation, or editorial additions of mine
are in [square brackets]).
"... For other geologists, however, the [Colorado] river has been
the source of quite different interests and controversies ever
since it was discovered. These interests are theoretical and have
to do with the general problem of how rivers are born and develop.
The Colorado is well suited to exploring this problem, whose most
significant questions in this context are: When and how did the
river come into being? When did canyon cutting and correlative
uplift occur? How quickly was the Grand Canyon cut? Why and how
has the river cut across the many belts of high ground astride its
course?"
"This paper considers the history of the Colorado River and its
Grand Canyon (fig. 1)[Not reproduced here]. To understand what
follows, it is important to remember two contrasting views
regarding the history of the Colorado River. The first is that
the river from birth has been part of an integrated drainage
system with a course approximating the present one; the second,
that the river is a dynamic entity changing through time and
constructed from segments of pre-existing drainages with courses
quite different from the present one."
"According to the first view, the river came into being pretty much
as it is today, and at some well-defined time such as the Eocene
[about 40 to 50 M.Y. ago]. A statement that is made about any
part of the river applies to the river as a whole; the entire
river is young, or old, as the case may be."
"The second view is that most rivers are continually changing
entities that have evolved from various ancestors and will
continue evolving into progeny whose configuration depends on
factors such as tectonism [mountain building] and climate.
According to this view, the answer to the question "When was the
Colorado River born?" can only be another question: How much
departure from the present configuration is one willing to
tolerate and still speak of the Colorado?"
"Also important is that the Colorado traverses two contrasting
terrains in Arizona. The first is the Canyon country, typified by
the Grand Canyon. This is highly dissected terrain, commonly with
much relief [change in elevation]. The second is the Colorado
Plateau country, typified by most of the Navajo and Hopi
Reservations (fig. 1), and characterized by low relief, wide
mature valleys, and scarps [cliffs] developed on beds of
contrasting resistance and retreating down structural slopes. The
Plateau country is older and more widespread than the Canyon
country, which is encroaching on it."
Lucchitta then relates the complete history of geological thought, to
date, on the formation of the river and the Canyon starting with John
Wesley Powell's first report in 1875. In short, early explorers
subscribed to View #1 described above. Those, like Powell, who
followed the river westward saw evidence for a long history and
proposed a "birth" of the drainage sometime near the beginning of the
Tertiary Period (65 to 40 M.Y. ago). In the 1930's and 40's,
geologists working eastward from the Great Basin saw evidence for a
much shorter history and proposed a "birth" date between 15 and 5
M.Y. ago. In the 1960's, Edwin D. McKee and several Ph.D. students
(including Lucchitta) began the polyphase View #2. As Lucchitta
(1989) puts it:
"The concept of a polyphase history for the Colorado River was
developed fully for the first time by McKee and others (1967)
[Evolution of the Colorado River in Arizona: Museum of Northern
Arizona Bulletin 44, 68 p.]. These authors accepted the antiquity
of the upper part of the drainage system, as documented by Hunt,
but could not accept a continuation of this drainage westward
through the Grand Canyon into the Basin and Range Province.
Instead, they proposed that the ancestral Colorado followed
roughly its present course as far as the eastern end of the Grand
Canyon, but then continued not westward, but southeastward along
the course of the present Little Colorado (fig. 1) and Rio Grande
Rivers into the Gulf of Mexico. In Pliocene time, a youthful
stream, emptying into the newly formed Gulf of California and
invigorated by its shortness and consequent steep gradient, eroded
headward and captured the sluggish ancestral river somewhere in
the eastern Grand Canyon area. It was then that the river became
established in its present course and the Grand Canyon was
carved."
"The concept is pivotal because it introduces the idea (even though
the point is not made explicitly) that drainage systems evolve
continually - and do so chiefly through headward erosion and
capture and in response to tectonic movements. During this
process, the configuration and course of a drainage system may
change so much that it becomes difficult and rather arbitrary to
continue calling the ancestral drainage by its present name."
(This interpretation of the Grand Canyon and Colorado River was also
presented to the general science public in a series of diagrams and
captions accompanying the Grand Canyon supplement map from the July
1978 issue of National Geographic). Lucchitta (1989) now proposes
that although the broad outline of this polyphase history is correct,
the ancestral Colorado did not flow southeastward to the Gulf of
Mexico, but rather followed much of its arcuate present course across
the southern end of the Kaibab Plateau which was not then so
topographically pronounced. The river continued northwestward ...
"... to an as yet unknown destination. After the opening of the
Gulf of California, this ancestral drainage was captured west of
the Kaibab Plateau by the lower Colorado drainage."
Lucchitta dates the development of the lower river around 5.5 M.Y.
ago. He then proposes that this drainage captured the upper river
and had carved the Grand Canyon by 1.2 M.Y. ago - a period of about 4
million years. This theory explains the old age appearance of the
upper river and the youthful appearance of the western Grand Canyon.
I have really only given an introduction to Lucchitta's (1989) paper.
He continues for the bulk of this paper with discussions of the
evidence and detailed descriptions of landscape developments during
the formation of the present Colorado River system in Arizona.
Finally after this long description of what "most geologists who know
about the geology of northern Arizona" say, we can address Austin's
remarks about whether the Colorado River was responsible for carving
the Canyon. As can be seen from Lucchitta's interpretation and
McKee's earlier version, it simply becomes arbitrary what you name
the ancestral drainage section that first established the route which
became the Grand Canyon! Therefore Austin's initial remarks are at
least partially true but certainly misleading. However his
implications that modern interpretations support his catastrophic
flood hypothesis are false. In my brief search, I never found any
articles which propose that ponding of lake waters and catastrophic
breaching of the Kaibab Plateau "dam" was in any way responsible for
the Grand Canyon. And I'm still looking for his "many geologists".
----------------
Steve
[Disclaimer: The opinions expressed here are my own
and should not be attributed to my employer]
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
:: ////// Steven M. Smith Office: (303)236-1192 ::
:: |----OO U.S. Geological Survey Message: (303)236-1800 ::
:: C > Box 25046, M.S. 973, DFC Fax: (303)236-3200 ::
:: \__~/ Denver, CO 80225 smsmith@helios.cr.usgs.gov ::
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::