Oct 252016
 

Basalt is a dark, fine-grained, basic (low silica) igneous rock, often extruded as molten lava from volcanic fissures. Its low silica content means it can flow easily, often building up over the years to form large plateaus. As the basaltic lava cools, it contracts and solidifies. An extensive network of cracks often develop in basalt, which may extend many meters deep. These cracks tend to leave columns between them which are roughly hexagonal (6-sided) in shape. Among the more famous examples of basalt columns or pavements in the world are Giant’s Causeway (Northern Ireland), Fingal’s Cave (Scotland) and Devil’s Postpile (California, USA).

The best known location in Mexico to see basalt columns is about an hour’s drive north of Mexico City, at Santa María Regla, in the state of Hidalgo. These columns, attractively located on the side of a canyon, with a waterfall tumbling over some of them (see sketch), were visited by the famous Prussian scientist/geographer Alexander von Humboldt, during his exploration of Mexico in 1803-04. Some individual columns are 40 meters tall.

Basalt prisms at San Miguel Regla

Basalt prisms at San Miguel Regla, from Humboldt and Bonpland, Vues des Cordilleres et monumens des peuples indigenes de l’Amerique.

The basalt columns of Santa María Regla are one of the locations described in The first geography fieldtrip guide in Mexico. They are also one of Mexico’s top 13 natural wonders.

Basalt prisms at Santa María Regla

Other locations in Mexico where basalt columns or prisms can be seen include a quarry between the towns of Jamay and Ocotlán (Jalisco), the south-facing slope of the hills overlooking the town of Chapala (Jalisco) and the Salto (waterfall) de San Antón (Cuernavaca, Morelos).

Mexico’s geology and landforms are analyzed in chapters 2 and 3 of Geo-Mexico: the geography and dynamics of modern Mexico.  Buy your copy of this book today!

Oct 122016
 

As vertical shafts go, this is a seriously deep one! Long considered to be “bottomless” (because no-one had ever managed to find the floor), we now know it is precisely 335 meters (1099 feet) deep, making it the deepest water-filled sinkhole anywhere on the planet.

The El Zacatón sinkhole is on El Rancho Azufrosa, near the town of Aldama in Tamaulipas in northeast Mexico. The sinkhole or cenote is one of several located in the same area, though recent studies have failed to demonstrate any obvious underground connections between them. The term cenote is a Spanish rendering of the Mayan word d’zonot, “a hole in the ground”. The El Zacatón pit, which is about 110 meters (360 feet) across and roughly circular, contains a deep lake. The water is warm (averaging about 30 degrees C), highly mineralized and has a sulfurous odor. The name El Zacatón comes from the floating islands of grass (zacate) which blow across this lake from one side to the other with the wind.

The Zacatón Sinkhole

The Zacatón Sinkhole

The pit’s depth has attracted serious divers for many years. In 1993, Dr. Ann Kristovich dove to a new women’s world record depth of 169 meters (554 feet). The following year, two American explorers tried to reach the bottom of the sinkhole. Jim Bowden successfully reached a men’s world record depth of 282 meters (925 feet) but still did not touch the bottom. Tragically, his diving partner Sheck Exley died during the attempt.

The mystery of the sinkhole’s depth was finally solved in 2007. A multi-million dollar exploration, mainly funded by NASA, trialled the Deep Phreatic Thermal Explorer (DEPTHX) robot, designed to explore ice-covered Europa, Jupiter’s smallest moon. Partners on the DEPTHX project include Carnegie Mellon University, Southwest Research Institute, Colorado School of Mines, The University of Arizona, and the University of Texas at Austin’s Jackson School of Geosciences. In the words of a NASA press release, The Deep Phreatic Thermal Explorer (DEPTHX) is a 3,300-pound, computerized, underwater vehicle that makes its own decisions. With more than 100 sensors, 36 onboard computers, and 16 thrusters and actuators, it decides where to swim, which samples to collect, and how to get home.

Exploring El Zacatón pit was considered to be an ideal preliminary test of the DEPTHX autonomous robot, which is about the size of a go-kart. The robotic vehicle successfully generated a highly detailed sonar map of the sinkhole, and obtained samples of water and biotic material from the walls, discovering several new phyla of bacteria in the process. Its next challenge is to explore beneath the ice of West Lake Bonney in Antarctica.

At El Zacatón, the sonar study showed that the sinkhole has a total depth of 335 meters: the lake is 319 meters deep at its deepest point, and its surface is 16 meters below the height of the sinkhole’s rim.

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Sources / Further reading:

Mexico’s geology and landforms are analyzed in chapters 2 and 3 of Geo-Mexico: the geography and dynamics of modern Mexico.  Buy your copy of this book today!

Sep 262016
 

Lake Chapala is Mexico’s largest natural lake. On the geological timescale of millions of years, all lakes are temporary features on the earth’s surface. Once formed, natural processes begin to fill them in and/or to drain them.

Map of Lake Chapala, Jalisco, Mexico. All rights reserved.

Lake Chapala resulted from drastic earth movements, accompanied by earthquakes and faulting which occurred some twelve million years ago. Lake Chapala collected on the floor of a rift valley. Movements along the parallel systems of faults that caused the rift valley still occur today. Evidence for this continued movement can be seen in the cracked or displaced walls of some local buildings.

Given its advanced age, it is not surprising to discover that Lake Chapala was once (thousands of years ago) much larger. In fact, though no-one has so far proven it beyond doubt, it may have been immensely large, covering an area seven times its present area, with a correspondingly long shoreline. At a later stage in its history, it became the deepest lake of an interconnected series of lakes which flooded the valley floors where the towns of Jocotepec, Zapotitan, Zacoalco and Sayula are today. The present Lake Chapala is thus probably only a small remnant of the original version.

The lake is under heavier pressure than at any time in its existence. Local towns and the nearby city of Guadalajara see it as an inexhaustible supply of domestic and industrial water. Tourists see it as a recreation resource, and the thousands of foreign retirees who have settled on its shores see it as a major reason for the area’s beneficial climate.

A case study of ‘residential tourism’ in the villages on the northern shore of Lake Chapala is discussed in chapter19 of Geo-Mexico: the geography and dynamics of modern Mexico.

The levels of flow of the River Lerma, the only river of any size entering the lake, are crucial to the health of the lake. In recent years, demands for Lerma water have multiplied many times over, principally for farms in neighboring states, but also for industries. All the other rivers entering the lake are much smaller and, with rare exception, flow into the lake only a few times a year during the rainy season. The hydrology of Lake Chapala is discussed in chapters 6 and 7 of Geo-Mexico: the geography and dynamics of modern Mexico.

The good news is that Lake Chapala was recently declared an Internationally Important Wetland by the Ramsar Convention, joining a large global network of similarly important wetland sites. The 13th International Living Lakes Conference was held in Chapala, March 22-25, 2010.

This is an edited excerpt from Tony Burton’s Western Mexico, A Traveller’s Treasury (4th edition) .

Cueva Cheve, Oaxaca, is one of the world’s deepest cave systems

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Apr 062015
 

Even though most people have never heard of it, Cueva Chevé is one of the deepest cave systems in the world. In 2003, a team led by American speleologist Bill Stone, explored Cueva Chevé, located in the mountainous, pine-clad Sierra de Juárez region of Oaxaca, to a depth of 1484 m (4869 ft). The Cueva Chevé system is thought to have some tunnels (as yet unexplored) that extend even further, to depths beyond 2000 m (6500 ft). By way of comparison, at present the world’s deepest known cave is the Krubera Cave, in the Republic of Georgia, which has a maximum explored depth of 2197 m (7208 ft).

Profile of Cueva Cheve

Profile of Cueva Cheve

How deep might the Cueva Chevé be?

In 1990, colored dye trace experiments showed that there was a hydrological connection between the Chevé Cave and a distant spring (resurgence). This shows that the Cueva Chevé system (including parts not yet explored) has a total vertical fall of 2525 m (8284 ft) over a distance of (north to south) of almost 19 km (11.8 mi).

Because the major risks in exploring any cave system include the possibility of sudden rises in water level, or unexpected water flows through the caves, expeditions to this region are limited to the middle of the dry season (ie February-April). When an expedition gets underway, staging camps are set up underground at intervals, but only in locations believed to be well above flood stage water levels.

Cueva Chevé (see cross section) is shaped like a giant L. The vertical shaft is about 910 m (3000 ft) deep and roughly 3.2 km (2.0 mi) of passages are required to get to the bottom. The remainder is a long, gradually sloping passage that goes on for another 3.2 km and drops roughly 605 m (2000 ft). The cave’s deepest known point is about 11 km (7 mi) from the entrance, where explorers have so far failed to get past a terminal sump.

The air in the cave is relatively warm, with temperatures ranging from 47-52̊ F (8-11̊ C).

Chambers so far explored have been given prosaic names such as “Cuarto de las Canastas” (the Basket Room), “Cuarto del Elefante Negro” (the Black Elephant Room), and “Cañon Fresco” (Fresh Canyon), while named cave formations include the “Taller de Santa Claus” (Santa Claus Workshop). Several parts of the cave system have been found to contain human artifacts, the earliest dating back at least several hundred years.

How to get there

Cueva Chevé is about 140 km (86 mi) north of Oaxaca City via highways 190 and 131.

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Where are the mining concessions in Mexico?

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Feb 022015
 

A series of graphics prepared by Mexico City daily El Universal includes a map showing the details of all the mining concessions in Mexico. According to the newspaper’s analysis, one fifth of Mexico’s total land area is subject to mining concessions belonging to one company or another.

The six companies holding the largest areas of concessions are:

  • Altos Hornos de México (364 concessions totaling 3208 hectares)
  • Fresnillo PLC (1009; 1953)
  • Industrias Peñoles (922; 953)
  • Minera Fresco (779; 889)
  • Cascabel (116; 749)
  • and Grupo México (711; 607).

The map is probably the single most interesting graphic in the series. Zooming in (top left of map) allows the details of each concession to be viewed, including the concession holder, size of concession, minerals involved and whether or not the concession is “active”. Is there a mining concession near you? You might be surprised. Even in an area of Mexico that I have known intimately for many years, there are two concessions that I have never previously heard of!

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The mystery of the Alarcon Rise

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Dec 292014
 

Geologists have discovered that some strange things are happening off the southern coast of the Baja California Peninsula.

In essence, while most of Mexico rests on the North American plate, the Baja California Peninsula is on the gigantic Pacific plate. The Pacific plate is moving slowly northwest and the pressures in the zone where these two plates intersect, under the Sea of Cortés (Gulf of California), has caused a complex series of parallel faults which (further north) link to the California’s San Andreas Fault system. Thus, the Sea of Cortés is an area of heavy seismic activity.

The Alarcón Rise is a 31-mile-long (50 kilometer) spreading center at the mouth of the Gulf of California. Along ocean spreading ridges like the Alarcón Rise, the seafloor is splitting apart as lava wells up from underneath. Credit: (c) 2012 MBARI

Location of the Alarcón Rise. Credit: (c) 2012 MBARI

The Alarcón Rise (see map) is a 50km (30 mi) long “bump” under the Sea of Cortés. New seafloor is being continuously created along the Alarcón Rise as undersea magma rises to the surface and cools to become lava. As the plates continue to move, this lave is then carried away to either side of the Alarcón Rise, allowing fresh lava to take its place, and so on. The rate of sea-floor spreading here is a relatively slow 5 cm (2 in) a year.

The Alarcón Rise has been studied in considerable detail by geologists attached to the Monterey Bay Aquarium Research Institute (MBARI) in California. Using a sonar-mapping robot, they discovered new deep-sea hydrothermal vents.

But their most surprising find was a “Weird Underwater Volcano.

In most zones of sea-floor spreading, the lavas are relatively low in silica and therefore free-flowing. Such lavas are known, on account of their chemistry, as “basic” lavas. (Lavas higher in silica, known collectively as acid lavas, tend to be more viscous and flow less easily. Acid lava volcanoes tend to erupt far more explosively than basic lava volcanoes.)

The curiosity of the Alarcón Rise is that while the vast majority of lava flows along the ridge are basic (basalt) lavas, those associated with at least one volcano are clearly acidic, not basic.

Researchers used a remote-control vehicle to collect samples and explore the volcano, which is 2375 m (7800 ft) below the surface. Samples of the lava show that it is primarily rhyolite with some dacite, with a silica content of up to 77%, the highest of any rock ever found along a mid-ocean ridge, according to Brian Dreyer, a geochemist at the University of California, Santa Cruz. The volcano with acid lava forms a small dome, about 50 meters (165 ft) in height and covers an area of about 1200 meters by 500 meters (4000 feet by 1640 feet). The dome is probably several thousand years old.

The lavas solidified quickly to form angular chunky blocks, some of which then rolled down the sides of the rise to form talus (scree). The individual blocks can be as large as cars or small houses.

The findings suggest that this particular volcano could give rise to hazardous eruptions. It is only 100 km (60 mi) from land and very close to the major tourist areas fringing the coast of Baja California Sur. Any major explosive eruption from this volcano could also cause a tsunami with the potential to devastate settlements on both coasts of the Sea of Cortés (Gulf of California).

Geologists are still working on trying to fully explain this apparent anomaly in lava composition. They have already discarded several ideas, and their current hypothesis is that the magma source was at some point contaminated by seawater, resulting in an unusually high concentration of volatiles such as water, sulfur and chlorine.

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Nov 132014
 

Mexico’s varied geography has made it a premier destination for all kinds of adventure tourism, from caving and canyoneering to jungle treks, white-water rafting and rock climbing.

This 6-minute video shows mountaineer Alex Honnold climbing the 460-meter (1500-feet) high rock face known as El Sendero Luminoso near Monterrey in northern Mexico. What makes this climb special (and slightly scary to watch) is that Honnold climbs solo and without any safety measures such as ropes.

Interviewed for National Geographic Adventure before he had seen the video, Honnold said, “I’m not sure what the video shows, but my true solo was all alone with no photogs [photographers] or helis [helicopters]. We then went back and filmed on big portions of it. In my mind there’s a clear difference between personal climbing—the actual solo—and work days—the filming afterward.”

"The Spires" in El Potrero Chico climbing area (Wikipedia photo)

“The Spires” in El Potrero Chico climbing area (Wikipedia photo)

The El Sendero Luminoso rockface is in an area known as El Potrero Chico, a short distance from Monterrey, near the town of Hidalgo.

The Wikipedia entry for El Potrero Chico describes it as having “a large range of different climbs, most of them in the 5.8 to 5.13 grade. The type of climbing can range from steep overhanging face to easy slab. The rock is usually quite sharp. The climbs are mostly situated in a canyon at the entrance of the park, while the interior offers undeveloped mountain terrain with many mountain biking routes, ranging from very easy to expert options.”

According to Wikipedia, El Potrero is “considered one of the top 10 locations to sport climb in the world. In addition to well over 500 routes, the area boasts the second longest sport route in North America, Timewave Zero, with 23 pitches and over 2,000 feet (610 m).”

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Cananea in Sonora: one of the largest open-pit copper mines in the world

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Oct 022014
 

One of the largest open-pit copper mines in the world, the Buenavista del Cobre mine in Cananea produced over 200,000 metric tons of copper in 2012. The mine, opened in 1899, is located approximately 40 kilometers south of the border between Arizona and Sonora, Mexico. The open-pit mine was estimated to contain 26.874 million metric tons of copper reserve as of December 2012.

This mine was the location of a 2014 toxic spill: Toxic spill in Sonora copper mine causes environmental disaster

mina-cananea

Source unknown. Used at http://www.labartolina.com.mx

The ore is refined at an on-site concentrator, which has a milling capacity of 77,000 metric tons/day. The concentrate output is transported to the smelter at La Caridad by rail. Also present are an on-site leaching facility and two solvent extraction and electro winning (SX/EW) plants, with an annual production capacity of 55,000 metric tons of copper cathode.

The active, 2-kilometer-diameter Colorada Pit (top right of image below) is recognizable in this astronaut photograph by the concentric steps, or benches, cut around its perimeter (see larger image). These benches allow for access into the pit for extraction of ore and waste materials.

Cananea Mine, Sonora (NASA Earth Observatory, March 2008)

Cananea Copper Mine, Sonora (NASA Earth Observatory, March 2008) Click to enlarge

Water (black) fills the bottom of the pit and several other basins in the surrounding area. The city of Cananea, marked by its street grid, is northeast of the mine workings. A leachate reservoir for removal and evaporation of water pumped from the mine workings is located to the east of the mine (image lower left). The bluish-white color of deposits near the reservoir suggests the high mineral content of the leachate.

sonora-cananea-mina_de_cobre

Source unknown. Credit: https://yoreme.wordpress.com/

Text: NASA’s Earth Observatory and The 10 biggest copper mines in the world

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Popocatepetl Volcano continues its very active phase

 Mexico's geography in the Press, Other, Updates to Geo-Mexico  Comments Off on Popocatepetl Volcano continues its very active phase
Aug 092014
 

Popocatepetl Volcano, near Mexico City continues to be very active, with smoke and ashes belching up to 1000 meters above the crater rim. Mexico’s National Disaster Prevention Agency Cenapred, reports that the volcano had 82 “low intensity” exhalations on 7 August 2014, four of which contained “explosive material”.

Popocatapetl, 8 August 2014. Credit: Cenapred.

Popocatapetl, 8 August 2014. Credit: Cenapred.

The agency also reported that many mionr tremors hd been recorded, including one harmonic tremor lasting 56 minutes. Geologists believe that the volcano is currently destroying dome number 50 even as dome number 51 begins to form. Dome #51 is currently about 70 meters in diameter. Renewed explosions, together with some ash fall is predicted for the coming days.

The Volcanic Traffic Light remains at Yellow Phase 2.

For a series of images dated 8 August 2014, see Images of 8 of ago of 2014

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Mexico’s geomorphosites: Ceboruco Volcano

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Apr 072014
 

A short distance west of the crater lake of Santa María del Oro, in the west Mexico state of Nayarit, is Ceboruco volcano which has a cobblestone road to the top. The road starts from the old and picturesque village of Jala, eight kilometers off the main highway (Highway 15). The cornfields around Jala yield some of the largest ears of corn in the world, more than 30 centimeters (one foot) in length, a cause for celebration in the village’s annual August festival. Jala was declared a Magic Town in 2012.

The road up Ceboruco is a geologist’s or biologist’s dream come true, a slowly unfolding series of volcanic forms and different types of vegetation with abundant surprises even for the scientifically expert. Small wonder, then, that the great German botanist Karl Theodor Hartweg was so impressed with Ceboruco when he collected plants here in the nineteenth century. To read more about his discoveries, see The geography of garden flowers, many of which originated in Mexico.

ceborucoNear the top are several short but interesting walks, some in shady, thickly vegetated valleys hidden between towering walls of blocky lava, some along the many overlapping rims of the various old craters of which this complex peak is comprised. Wherever you choose to walk, a multicolored profusion of flowers and butterflies will greet your eyes.

On the south side of an attractive grassy valley at kilometer sixteen, fumaroles send hot gases and steam high into the air reminding us that this volcano is not yet irrevocably extinct. A massive Plinian eruption in about the year 1000 sent ash plumes into the air and devastated a wide area around the volcano. The huge blocks of lava near the summit date from a prolonged series of eruptions in the early 1870s.

Highway 15 cuts through Ceboruco’s lava field a few kilometers after the Jala junction. For those not wishing to brave the cobblestone road up to the volcano, this is a good place to stretch the legs and marvel at the inhospitable, black lava blocks which were spewed out more than a hundred years ago.

This is a lightly edited extract from my “Western Mexico: A Traveler’s Treasury” (link is to Amazon’s “Look Inside” feature), also available as either a Kindle edition or Kobo ebook.

Want to read more about Mexico’s geomorphosites? The link uses Geo-Mexico’s “Site Search” feature.

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