GEOLOGIST QUESTIONS "DIFFERENTIAL EROSION" AT CYDONIA
GEOMORPHOLOGY AT CYDONIA
By James L. Erjavec
Copyright © 1996 by James L. Erjavec
(Notes and editing by Stanley V. McDaniel, author of The McDaniel Report)
ABOUT THE AUTHOR: James L. Erjavec has an M.S. in geology from The
University of Arizona, Tucson, Arizona, and a B.S. in geology from The
Cleveland State University, Cleveland, Ohio. He is a geologist and
Computer/Geographic Information System (GIS) Analyst with over 13
years experience in those fields. A specialist in mapping and computer
graphics, he has developed an extensive geomorphic feature map of the
Cydonia region to assist in the establishment of a geologic baseline
for continued studies.
The paper presented below is a shortened form of a longer piece titled
"A Geologic and Geomorphic Investigative Approach to some of the
Enigmatic Cydonia Landforms." It is important to consider Erjavec's
paper in relation to NASA's claim that the debated landforms at
Cydonia have already been subjected to a thorough scientific study.
From Erjavec's discussion it would appear that NASA geomorphologists
who maintain that the debated Cydonian objects are simply a result of
"differential erosion" have not had the last word on this subject and
that there is much to learn. For further information regarding the
longer version of this paper or the accompanying geologic map of the
Cydonia area, write The McDaniel Report, 1055 W. College Ave. #273,
Santa Rosa CA 95401.
NASA's Position Based on Differential Erosion
Broad generalizations by NASA, which have been based in part on
previous geologic studies of the Cydonia region of Mars, have been
inadequate to definitively explain the origins of the varied surface
features of Cydonia. During the development of a geomorphic feature
map of the area of Cydonia bounded approximately by the 40N to 41.5N
degree latitude lines and the 11W to 7W longitude lines (an area
covered by Viking Frames 70A11, 70A12, 70A13, 70A14, 70A15, 35A72 and
35A74), a preliminary study of the landforms has been conducted,
including both anomalous and "ordinary" forms.
The argument that NASA has evidently relied on to debate the anomalous
nature of the morphologies of the Face and other enigmatic Cydonian
landforms is based on the premise that the Martian northern lowland
plains were at one time covered with a kilometer or more of "erodible
sediment." The origin of the landforms has been attributed to a
differential erosion process that removed an overlying cratered
plateau material, leaving a knobby terrain that is a combination of
exhumed remnants of cratered terrain, igneous intrusives or cratered
plateau material (Guest, 1977).
Inasmuch as popular scientific literature appears to have accepted
this view without reservation, it is not uncommon to find references
to Cydonian landforms that typically cite their origins as the
exclusive result of wind erosion (Henbest, 1992) without considering
the validity of the data and assumptions that support such claims.
Differential Erosion not a Likely Cause
But more recent evidence (McGill, 1989) has been provided that refutes
claims that over a kilometer of sediment was eroded from the Martian
northern lowland plains. McGill has used crater dimensional equations
to conclude that only a slight to modest erosion of the northern
lowland plains could have occurred since Noachian times and that at
best, 200 meters of material may have been stripped off the plains.
This is corroborated by Maxwell (1989) who shows that there is little
correlation between the Martian landform dichotomy (northern lowland
plains and southern cratered uplands) and the trends of scarps and
ridges of the landforms.
Cattermole (1992) states that because a series of closely related
geologic events have affected the northern plains (McGill, 1987;
Phillips, 1988; Frey and others, 1988; Wilhelms and Baldwin, 1989) and
because there is a lack of evidence for where the 2 to 3 kilometers of
eroded sediment has been transported, there is little probability that
erosion was the driving mechanism for the lowering event. Instead he
believes that the evidence suggests the lowering of the northern
plains was a result of some (to-date) uncertain internal mechanisms.
This study corroborates the findings of the above-mentioned authors on
the basis of geomorphological and geological analysis of Cydonian
landforms. To start with, the dimorphic distribution of impact craters
between the knobby terrain and cratered plain in this area of Cydonia
weakens support for an extensive pre-plain overburden. The knobby
terrain contains several large impacts greater than 1 km in diameter,
but relatively few craters below this threshold. The pediment surface,
situated mostly eastward of the knobby terrain, has a similar
distribution of large impacts (> 1 km), but contains a significantly
greater number of smaller craters (< 1 km).
On its most basic level, this dimorphism suggests there is a distinct
geomorphic difference between the cratered and knobby terrains that
cannot be accounted for if exhumation by erosive forces has been the
primary factor in this area's morphological development. If one rules
out random impacts alone as a means of origin for this dimorphism (and
statistically there is no reason to attribute it to random cratering
because age determination for Martian surfaces have been based on
impact crater rates and densities (Carr, 1981, Tanaka, 1986), either
different geologic/erosional processes have been at work in these two
terrains or the two surfaces had origins in markedly different
morphologies or more likely a combination of both have occurred.
To verify the authenticity of this apparent cratering dimorphism,
crater counts (<1 km) were performed for the knobby and cratered
terrains with the following results: The average for the cratered
plain: 8800 craters/100,000 sq. km The average for the knobby terrain:
2000 craters/100,000 sq. km Ratio cratered/knobby: 4.4/1.
Even factoring in craters that appear to have suspect impact origin
(i.e. craters following distinct linear trends or fractures, crater
morphologies signifying possible origin from liquefaction(?) or
volcanic(?) processes, etc.) the following results have been obtained:
Cratered plain: 9700 craters/100,000 sq. km. Knobby terrain: 4900
craters/100,000 sq. km. Ratio: 2/1
Since this study is still preliminary in nature, definitive
conclusions as to the origin of this cratering ratio have not been
drawn at this time, but the cratering bimodal distribution appears to
cast doubt on claims that this area was subjected to a differential
erosion of at least 1 kilometer of soft, overlying sediment and that
the landform morphologies (knobs, hills, ridges, etc.) are primarily
the result of that process.
Using NASA's view one would have to accept that differential erosion
selectively eliminated nearly all evidence of small impacts on the
knobby terrain while leaving the cratered plain nearly untouched. A
more likely answer (from the evidence at Cydonia) is that landform
development was the result of a geologically interrelated set of
processes of both constructive and destructive nature which provided
the present character of the Cydonian surface.
Cydonia Landforms Remain Enigmatic
NASA's geological interpretation of Cydonia is even inadequate to
explain the definitive "natural features." Furthermore despite NASA's
approach, the particular Cydonian landforms in question have retained
their anomalous character.
The Face has been argued to be nothing more than an optical illusion
or a trick of shadows. Those arguments appear to be based more on
conjecture than on substantive geomorphic or geologic evidence. Since
the two images (Viking frames 35A72 and 70A13) containing the Face
were taken under a 17 degree difference in solar lighting angle, the
persistence of internal features in the Face precludes the latter
possibility. Thus the questions remaining are the authenticity of the
morphology of the Face and its possible origin.
After considerable review of the Face and other Cydonia landforms, the
conclusion can be drawn that the morphology of the Face is not a
result of an optical illusion. To the contrary, under the variation in
illumination angles between images 70A13 and 35A72, the features of
the Face change little, indicating that the origins of the "eyes,"
"mouth" and other features are likely the result of a variation in
surface morphology rather than shadows cast by as of yet indeterminate
A comparison of the Face in frames 70A13 and 35A72 to some nearby
mesas also depicted in those frames corroborates the validity of the
Face's morphology. Using one mesa approximately 13 km due east of the
Face as an example, NASA's argument that the Face's morphology is an
illusion is further contradicted. This mesa has a steep-walled ridge
running lengthwise through its center and appears to contain a remnant
impact crater (1 km diameter) in its northern half. Because of the low
solar angle in 35A72 the shadows are heavy, obscuring some of the
central features on the eastern slope of the landform. In 70A13, the
greater solar angle allows for more of the shadowed eastern side in
35A72 to be discerned.
Though it is apparent that the two images of this mesa are slightly
different due to shadowing effects, the general trends within the mesa
are persistent. Not only does the definition of the sunward side of
the mesa appear to change little between images 35A72 and 70A13, the
definition of the ridge becomes more pronounced, revealing the
ruggedness of its eastern slope.
It is obvious that in viewing the images of this mesa, its general
morphology is authentic despite slight definition changes between the
images. Similar observations of the definition changes in the Face
between those images indicates that the same logic can be applied.
Thus to conclude that the morphology of the mesa is authentic (and it
is difficult to dispute that) after inspection of the images, it
follows that the morphology of the Face must be authentic as well. In
fact, there are less visual changes in the morphology of the Face
between images 35A72 and 70A13 than are noted in the mesa. Using
NASA's arguments of light and shadow or optical illusion, one might be
predisposed to conclude that the features of the mesa are more
suspicious than those of the Face.
An analysis of other landforms in this area supports the above
conclusions, but could the morphology of the Face be the result of a
random series of geologic events? Undoubtedly that is a possibility,
but the landform's obvious humanoid characteristics and societal
implications, in combination with other enigmatic landforms at
Cydonia, requires that a more thorough geologic evaluation of Cydonia
be pursued to acquire a resolution to this problem.
The "Cliff" is actually an elongate mesa 18 km NE of the Face,
apparently overlaying an ejecta blanket of a 3 km impact crater. The
Cliff contains a thin, almost linear central ridge running the length
of it. NASA has relied on the Cliff's relation to the nearby impact
crater in an attempt to explain its origins. Anonymous NASA evaluator
"Mr Q" (see The McDaniel Report, page 109) has stated the adjacent
crater to be a tuff ring or similar volcanic feature.
This statement is erroneous on even the most basic level. Cursory
observation of this crater immediately indicates its formation from
impact. The impact is surrounded by rampart-style ejecta ("Yuty-type")
and displays all of the features of a rampart crater, including
characteristic overlapping sheets of ejecta with lobate margins,
raised rims along the ejectamenta's outer edges and the extension of
ejecta about two crater diameters away from the impact. Though it has
been determined to date in this analysis of Cydonia that there is more
geomorphic evidence suggesting (at least isolated) volcanic activity
than recognized in previous studies, this crater is of unquestionable
Malin (see The McDaniel Report, pp. 109-110) indicates that the Cliff
is a product of stratigraphic superposition and differential erosion.
In this current study, the detailed analysis of the variety of
geomorphic features in Cydonia does not support a primary reliance on
differential erosion as a means of landform development. Evidence of
differential erosion is present in Cydonia, but not to the degree that
Malin suggests. Additionally, if the Cliff is a relic mesa derived
from an extensive preexisting surface, there is no supporting evidence
for that, either in the crater or on its ejectamenta.
Also, no evidence has been found for the remnants of this preexisting
surface in association with any of the other ejecta blankets of
significant impact craters (> 1 km) in this area. To date, the "Cliff"
appears to be an isolated event. Another argument might be that only
this impact had any of the preexisting surface deposited on it, but
without sediment deposition in the impact crater itself. Is such a
restrictive solution geologically plausible or provable? And what
questions would that pose for the feasibility of the depositional
A third possibility is that the "Cliff" existed before the impact, but
there is no evidence of the ejecta having overlain the Cliff, though
the ejecta flow extends beyond the Cliff for at least a kilometer.
There is also no evidence to imply that the Cliff is associated with
the impact event itself. If the Cliff predated the impact, it would
seem logical for some of the impact's ejecta to have overlain the
Cliff or at least to have flowed around the base of the Cliff as is
known to have occurred in other landforms/impact associations in
Cydonia, but there is no evidence for that either.
Since ejecta appears to resist erosion as shown by the numerous
pedestal craters on Mars, if ejecta had been thrown on the Cliff,
trace evidence of that event might be expected to be found. Again,
nothing. Because of the general lack of evidence for any definitive
explanation for the Cliff's origin and its timing in relation to that
of the adjacent impact, the Cliff and associated cratering event
Other evidence that undermines the Cliff's origin as a differential
erosion product are the trends within the various groupings of small
pedestal craters (< 1 km) that dot the cratered plain. These groupings
suggest that this area was not buried with soft sediment to the degree
that Malin claims. The alignments and groupings of pedestal craters
moreover provides evidence of a preexisting topographical surface that
was much thinner than that suggested by Malin.
The Tholus at Cydonia (name not to be confused with other "Tholus"
names designating volcanic vents on Mars) is an isolated,
semi-circular, mound-like landform that lies in the cratered plain
(J-12). The mound ("tholus" means "mound") is of relatively low relief
in relation to the knobby terrain to the west. It appears to contain a
thin depression or groove that circles the landform at its base and
spirals up toward the landform's peak in a clockwise fashion cutting
through the mound.
Another similar mound, Tholus-A, lies approximately 20 km to the south
of the Tholus and is about one-third the size of the Tholus. It too
contains a groove that spirals from its base to the peak, but the
spiral is counterclockwise. The smooth gradation in elevation present
in the Tholus is less evident in Tholus-A. The spiral almost appears
to be the result of a low escarpment which winds up the feature.
A third elliptical hill lying about 8 km of the Tholus sits on the
edge of what appears to be a meandering scarp line that runs
southwest/northeast. Though the general shape is similar to the Tholus
and Tholus-A, this landform has a steeper gradient. A fourth
low-relief mound (F,G-14) is located about 25 kilometers southeast of
the Tholus in a line with the above mentioned landform. This mound
appears to be eroded remnants of a larger landform and does not
exhibit any of the symmetry of the Tholus.
These features are surrounded by a number of small impact craters in
various stages of degradation. Some are fresh, others eroded into
pedestal craters and others eroded to remnants of their original form.
The Tholus, and to a lesser degree Tholus-A, stand in stark contrast
to the surrounding landforms. They display no evidence of volcanism,
are not impact-related and are difficult to explain as remnants of
larger non-distinct landforms because of their symmetrical shapes and
uniform, low gradients. Their lack of ruggedness or mesa-like
appearance makes both landforms enigmatic and problematic to other
landforms in this area.
The above-discussed Cydonia landforms are but a few of the problematic
landforms in this area. To lessen their possible significance by
explaining them as erosional remnants of a preexisting surface,
without supporting evidence, is clearly not a rigorous scientific
approach. To the contrary, what exactly is needed are "more rigorous
geologic evaluations" to determine the origins of these controversial
This review has pointed out inconsistencies in previous geologic
arguments and indicates, at the very least, that geologic
generalizations are not an acceptable method to explain surface
features in Cydonia, enigmatic or not. Such "ballpark" solutions add
little to the resolution of the landforms under study. The Cydonia
landforms may ultimately turn out to be no more than an odd assortment
of enigmatic natural features, formed by random geologic processes,
but they may as well turn out to have significant implications for
humanity. An unbiased approach assumes neither, but strives for the
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