See
Landsat V image.
Ward, Weide, and
Back (1985:1-117) give a
thorough coverage of the geology and hydrogeology of
Yucatan. They say:
Physiography: The Yucatan Peninsula is part of the Gulf Coastal Plain
Province of Mexico. As all surficial rocks of the peninsula are carbonates,
it displays a wide variety of karst features. The degree of karstification
and local relief is closely correlatable to the elevation of the region and
the depth to the water table.
Four distinct physiographic regions can recognized (Fig. 5). They are: 1)
Northern Pitted Karst Plain, (2) Sierrita de Ticul, (3) Southern Hilly Karst
Plain, and (4) Eastern Block-Fault District [where Muyil is located]. . . .
The Eastern Block-Fault District (Isphording, 1975) parallels the
Caribbean coast from northern Belize (N of the Maya mountains) to the vicinity
of Tulum, Quintana Roo. (Weide 1985:2)
They
further say, about the Eastern Block-fault District containing Muyil:
This area extends along the Caribbean coast of the peninsula. The
topography is characterized by a series of NNE-trending ridges and depressions
which reflect the occurrence of horst and graben blocks of the Rio Hondo Fault
Zone. Isphording (1975) noted the alignment of streams, lakes, and swales in
this region; e.g., Rio Hondo and Lakes Bacalar and Chunyaxche [close to the
Muyil site.] Locally, elevations may exceed 200 m, but most of this
district has elevations of 50-100 m. Relief is generally about 25 m
but may be greater in local areas adjacent to faults of greater displacement.
(Weide 1985:3)
In a paragraph about hydrography and hydrogeology they state that
"North of approximately 19°N
latitude there are no surface streams . . ." (Weide 1985:3)
Mason (1926:160) reported that the stream channel from the Chunyaxche
Lagoon to Boca Paila was the most northerly river he had heard of on the Yucatan
Peninsula. This channel, now known as Cayo Venado, at 20°N
latitude, provides access to the sea for Muyil.
As further pointed out by Weide (1985:16), who used satellite images in
his analysis, lines of cenotes trending NNE have developed along the
fault lines. These are the origins of both the Muyil Lagoon and the Chunyaxche
Lagoon, together with several other cenotes (Chunkopo, Tulum) visible on the
images and maps of the region. Walking northward from Muyil toward Coba, one can
easily observe the rapid rise and fall of the surface due to these fault lines
in the limestone. Aerial photos and satellite images fail to reveal the
numerous additional cenotes and fracture features that can be seen on the
ground.
At Muyil, the karstic limestone shelf, at an elevation of 6-8 m,
ends rather abruptly, forming the obvious eastern boundary of the site. The
terrain drops quickly to the coastal lagoons, which are themselves 50-200 cm
above sea level. Virtually all structures at the site occupy the high ground
to the west of the edge of the shelf. The low ground to the east of the site is
marshy, and/or floods seasonally, and is not suitable for habitation. The site
center has a large collapse zone, and most of the major architecture at the site
is arrayed around the perimeter of the collapse. The collapse is not complete.
That is, the surface limestone has not fallen into the water table to form a cenote.
The collapse forms a 2-2½-m-deep, flat-bottomed depression with
sharp edges and with scattered large pieces of the broken limestone surface. In
places the edge of the collapse zone provides access to underground caves and to
sascaberas — small mines that were a Maya source of rotted limestone (sascab)
used for making stucco and mortar. The caves, with their possible religious
significance, the sheltered, easily-defended sea access, and the variety of
subsistence opportunities (slash-and-burn corn-farming, game animals, birds,
fresh- and salt-water fish and molluscs) at Muyil may have made the site
appealing to its early settlers.
Muyil is located within the Sian Ka'an
Biosphere Reserve, which
was established in 1985 as a large ecological preserve extending southward along
the Caribbean coast from Tulum. The Sian Ka'an staff compiled the following
information about the area: There are two geological formations. The Carrillo
Puerto Formation, dating to the Quaternary (Miocene-Pliocene), forms the
karstic limestone shelf with a typical elevation of 10 m. The more recent
formation (Pleistocene-Holocene) makes up the low coastal lands of freshwater
lagoons, brackish marsh, and seasonally-flooded grasslands that are so prominent
to the south of Tulum, but absent to the north. The topographic profile by A. López (Sian Ka'an 1983:27) is
typical of the Muyil archaeological zone. Within the zone one finds medium
forest (15-20 m high), cenote zones and fractures, low forest,
mangrove swamp, and seasonally flooded grasslands. Adjacent to the zone are
freshwater lagoons and petenes (raised islands of high ground, capable of
supporting tall trees, surrounded by seasonally-flooded lowlands). Close by is
the coast, with brackish bays, sand dunes, and the ocean. This author's tests
show that water salinity at the surface ranges from zero in the Muyil Lagoon,
the Chunyaxche Lagoon, and most of Cayo Venado to 18 ppm in the Caribbean
adjacent to Boca Paila. The striking contrast in the ecological zones is most
apparent in the false-color image of the Landsat-V Thematic Mapper.
Photograph 1
Landsat V Thematic Mapper false-color image of the Muyil region.
Click below for
high-resolution copy 700kb.
In the Landsat-V image,
computer-generated false colors from the Thematic Mapper bands 2, 3, and 5 (of
seven available) highlight individual ecological zones as follows:
Other features stand out in this image, including a
cloud over the northeast corner of the Chunyaxche lagoon whose shadow may be
seen slightly to the west of the cloud. The cloud and its shadow show the sun
angle at the time the image was taken (morning sun). In addition, one may
observe the coastal highway (within the red zone), and the small unpaved roads
connecting the two small lagoons with the highway. A small one-lane trail was
bulldozed northward from the west side of the highway (approximately due west of
the northern edge of the Chunyaxche lagoon. This trail runs to the north, then
bears to the northwest ending in a slight curve near a cenote. The
intersection of this trail with the highway marks the northern-most survey point
of the Muyil A protected zone. The portion of this trail bearing northward from
the highway is a part of the boundary line dividing Ejido Chumpom from Ejido
Pino Suarez. Two critical watercourses visible in the image form a part of
the Muyil access route to the Caribbean — the short outflow canal from the
Muyil lagoon to the Chunyaxche lagoon, and Cayo Venado, the creek that begins
its course at the northeast corner of the Chunyaxche lagoon (by the cloud and
the temple labeled Xlahpak [Vigía del Lago]) and flows first northeast,
then southeast to the brackish lagoons near the coast. There are numerous fossil
shorelines and water level artifacts visible in the Landsat-V image, and
many of the larger ones are also visible in aerial photos of the region.
The Muyil site is just north of the label 'Chunyaxche' in the image. No
structures are resolvable in the 30-m satellite data, but the cleared area of
the site near the entrance, including the Castillo, is visible due to its
absence of vegetation. The edge of the karstic shelf (and the accompanying
elevation change of about 6 m) is clearly marked by the change of
vegetation from medium forest (dark red) to mangrove and grasslands (orange and
tan.) The computer analysis of the imagery and the photo were graciously
supplied by Charles Duller of NASA Ames. The interpretation above is my own,
based upon ground-truthing numerous areas in the region.
Prevailing winds are from the sea (NE 40 percent, SE 22.7 percent) (Sian
Ka'an 1983:28). Precipitation is lowest in March (29.4 mm) and highest in
September (208.1 mm) and the annual average for 1967 - 1982 was 1128 mm.
(Sian Ka'an 1983:29) Average
temperatures range from 22°C
in January and February to 27.8°C
in May with average highs and lows of 33°-36°C and 9°-18°C.
(Sian Ka'an 1983:30) Humidity is
approximately 80 percent. The coast is exposed to Atlantic hurricanes
following a southern track toward the Gulf of Mexico, and twelve have passed
close to Muyil in the last 89 years. The most recent was Gilbert in 1988.
The modern Maya willingly acquaint archaeologists with the two seasons,
wet and dry, that determine their annual round of activities. The rainy season
begins in mid-May to mid-June and lasts until very late in the year. The dry
season lasts from late December through early May. This seasonal round drives
the agriculture of the area, with milpa-clearing performed in March and
April and burning of cleared fields in late April and early May. Planting is
done just prior to the start of the rainy season. Rains are encouraged by the
local Maya with a Cha-chac ceremony, often held within the Muyil
protected archaeological zone. In my limited experience, rains closely follow
the ceremonial consumption of the Maya beer, balche, by village elders
during this ceremony to the rain gods. Corn-grinding stones (manos and metates)
from ancient contexts at Muyil, plus lack of evidence of significant climate
changes during the past two thousand years, support the assertion that this
single-planting seasonal round was in use in the Muyil area in preconquest
times.
In the medium forest, the dominant trees reported are Manilkara zapota
(the zapote, whose sap supplies chicle for chewing gum), Metopium brownei, Bursera simaruba, and Lysiloma
latisiliquum. At Muyil, Brosimum
alicastrum (commonly called ramón
or breadnut) is common, though not
generally common throughout the forest elsewhere (Sian Ka'an 1983:71).
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