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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.

Landsat V 1.JPG (736966 bytes)

            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:

            deep red                       medium forest 

            lighter red, tan               disturbed forest, old milpa

            isolated red patches       petenes

            dark blue                      deeper part of lagoons

            light blue                       shallower part of lagoons

            orange                          mangrove swamp

            yellow/tan                     grasslands

        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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