Common errors of Mexican geography #2: confusing the Sierra Madre with the Volcanic Axis

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Jun 192014
 

Describing somewhere in Mexico as being “located in the Sierra Madre mountains” may conjure up images of high, possibly snow-capped peaks and rugged scenery, but does very little to pin down the location. Mexico has several Sierras Madre (literal translation: Mother Ranges). The three main Sierra Madre regions in Mexico are the Western Sierra Madre, Eastern Sierra Madre and Southern Sierra Madre (see map).

The Western Sierra Madre (Sierra Madre Occidental) is the youngest, highest and most viciously dissected of the three. This region includes the scenically amazing Copper Canyon region we have described in many previous posts, including:

Location of Volcanic Axis and Monarch Butterfly reserves

Location of Volcanic Axis and Monarch Butterfly reserves. Basemap: Figure 3.1 of Geo-Mexico; all rights reserved.

The Western Sierra Madre extends only as far south as the states of Nayarit and Jalisco.

Its counterpart on the eastern side of the country is the Eastern Sierra Madre (Sierra Madre Oriental) which is older, lower and less rugged. Between these two major mountain ranges are mid-elevation basins and plains.

At the southern end of both the Western Sierra Madre and the Eastern Sierra Madre is the Volcanic Axis.

The Southern Sierra Madre (Sierra Madre del Sur) lies south of the Volcanic Axis, largely in the state of Oaxaca.

The details of Mexico’s physiographic regions are complex, but the basic relief pattern of these three Sierra Madre regions, separated by the Volcanic Axis and mid-elevation basins and plains, is fairly simple. It is therefore disappointing when we read references to the Sierra Madre regions that are geographically inaccurate.

The Monarch Butterfly reserves, for instance, are regularly described as being in the Sierra Madre, or the Western Sierra Madre, even though they are located hundreds of kilometers away from the Western Sierra Madre, on the southern edge of the Volcanic Axis (see map). In the original National Geographic article about the “discovery” of the Monarch Butterflies’ overwintering sites (August 1976), the location of the butterflies was deliberately left vague (to prevent human-induced disruption of the sites), so that article can readily be excused for mislocating the sites as being in “Mexico’s Sierra Madre”. (The tiny map that accompanied that article also shifted the Monarch’s wintering areas well away from their real position.)

Despite the efforts of the National Geographic, it was not long before journalists published articles giving the precise locations of the sites, and visitors started to flock to see this marvel of nature. The establishment of reserves has now brought a measure of sanity and control to access and most visitors now behave respectfully.

One of the latest in the long line of journals and magazines to erroneously refer to the site of the Monarch reserves as “in the remote Sierra Madre mountains” (but lacking the original excuse of the National Geographic) is the Canadian Geographic in its December 2013 Annual Wildlife Issue. The general tone of the article is helpful, and it rightly emphasizes the need to protect habitat along the entire migration route between Canada and Mexico, so why mar the overall quality by making such a basic error of Mexican geography? Let’s help educate readers by making it clear that the Monarch Butterfly reserves are not in any Sierra Madre, but are in the Volcanic Axis!

Mexico’s 15 physiographic regions

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Jun 092014
 

The relief and landforms of Mexico have been greatly influenced by the interaction of tectonic plates.

The resulting relief patterns are so complex that it is often claimed that early explorers, when asked to describe what the new-found lands were like, simply crumpled up a piece of parchment by way of response.

The map below shows Mexico’s main physiographic regions. The core of Mexico (both centrally located, and where most of the population lives) is the Volcanic Axis (Region 10 on the map), a high plateau rimmed by mountain ranges to the west, south and east. Coastal plains lie between the mountains and the sea. The long Baja California Peninsula parallels the west coast. The low Isthmus of Tehuantepec separates the Chiapas Highlands and the low Yucatán Peninsula from the rest of Mexico.

Mexico's physiographic regions

Mexico’s physiographic regions. Color version of Figure 3.2 of “Geo-Mexico, the geography and dynamics of modern Mexico”; all rights reserved.

We looked in more detail at the Volcanic Axis in several previous posts, including

and will look more closely at some of the other physiographic regions in later posts.

How similar are Mexico’s two major deserts, the Sonoran Desert and the Chihuahuan Desert?

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May 292014
 

There are four desert areas in North America. Two of these areas (Great Basin and Mojave) are in the USA. The other two (the Sonoran Desert and the Chihuahuan Desert) are almost entirely in Mexico, but extend northwards across the border. The Sonoran Desert includes most of the Baja California Peninsula, together with the western part of the state of Sonora. The Chihuahuan desert is the northern section of the Central Plateau, including the northern parts of the states of Chihuahua.

The Chihuahuan Desert has been intensively studied by scientists interested in the possibility of life on Mars – see this New York Times article: Learning About Life on Mars, via a Detour to Mexico.

In a previous post – Why is northern Mexico a desert region? , we saw how the combination of the descending air of the Hadley Cell, which results in surface high pressure, and the effects of rain shadows resulting from neighboring mountain ranges contribute to the low annual rainfall total characteristic of both Mexico’s desert areas.

deserts-colorWhile these two deserts both experience an arid climate, they also have many differences.

Area

The Sonoran Desert has an area of about 311,000 square kilometers (120,000 sq mi). The Chihuahuan Desert has an area of about 362,000 square kilometers (139,769 sq mi).

Elevation

The Sonoran Desert is lower in elevation that the Chihuahuan Desert, with some parts (in the USA) lying below sea level. The Chihuahuan Desert varies in elevation from 600–1675 m (1969–5495 ft).

Summer temperatures

The Sonoran Desert tends to have higher summer temperatures than the Chihuahuan Desert, though even in the Chihuahuan Desert, daytime temperatures in summer are usually between 35 and 40̊C (95-104̊F).

Seasonal rainfall patterns

The ratio of winter to summer rainfall decreases from west to east. Most of the Sonoran Desert (to the west) has a bimodal rainfall regime with spring and summer peaks. On the other hand, most of the limited rain that falls in the Chihuahuan Desert comes in late summer.

The Chihuahuan Desert has a mean annual precipitation of 235 mm (9.3 in), though annual totals vary from 150 to 400 mm (6–16 in).

Vegetation, fauna and biodiversity

These seasonal rainfall differences result in significant differences in the vegetation of the two areas.

The bimodal precipitation in the Sonoran Desert provides two flowering seasons each year. Some plants bloom in spring, following winter rains, while others flower in late summer, following summer rains. Typical plants in the Sonoran Desert include columnar cacti (Cereus spp.) such as sahuaro, organ pipe, and cardon, as well as many other types of cacti, including barrels (Echinocereus), chollas (Opuntia spp.) and prickly pear (Opuntia spp.). Other succulent plants are also common.

More than 60 mammal species, 350 bird species, 20 amphibian species, 100 reptile species, 30 native fish species, 1000 native bee species, and 2000 native plant species have been recorded in the Sonoran Desert. The Sonoran Desert includes the Colorado River Delta, which was once an ecological hotspot within the desert, fueled by the fresh water brought by the river, though this flow has become negligible in recent years. See, for example, Will the mighty Colorado River ever reach its delta?

The vegetation of the Chihuahuan Desert is dominated by grasslands and shrubs, both evergreen and deciduous. Common species include tarbush (Flourensia ternua), whitethorn acacia (Acacia constrictor) and creosote bush (Larrea tridentata). The Chihuahuan desert has small cacti; succulent agaves (Agave spp.) and yuccas. Plants bloom in late summer, following the summer rains.

The Chihuahuan Desert is home to about 350 of the world’s 1500 known species of cactus, and includes the fascinating area of Cuatro Ciénegas, which has an unusually high number of endemic plant species and is one of the world’s richest hotspots for locally endemic cacti.

The Chihuahuan Desert is considered to be one of the three most biologically rich and diverse desert ecoregions in the world, rivaled only by the Great Sandy Tanmi Desert of Australia and the Namib-Karoo of southern Africa. However, settlements and grazing have heavily degraded the natural vegetation of some parts of the Chihuahuan Desert.

he Chihuahuan Desert has about 3500 plant species, including up to 1000 species (29%) that are endemic. The high rate of endemism (true for cacti, butterflies, spiders, scorpions, ants, lizards and snakes) is due to a combination of the isolating effects of the basin and range topography, climate changes over the past 10,000 years, and the colonization of seemingly inhospitable habitats by adaptive species. See here for more details of the flora and fauna of the Chihuahua Desert.

Landforms

This basin and range landscape of the Sonoran Desert trends north-northwest to south-south-east. Parallel faulted blocks are separated by alluvial bajadas (broad, debris-covered slopes), pediments and plains, which become wider approaching the coast. Despite being a desert area, this region exhibits many features that have resulted from water action, including wadis, salt flats, stream terraces and alluvial fans.

For a fuller description of the landforms of the Sonoran Desert, see this extract from A Natural History of the Sonoran Desert (edited by Steven J. Phillips and Patricia Wentworth Comus) published by the Arizona-Sonora Desert Museum.

The Sonoran Desert includes the subregion of the Sierra of Pinacate (part of El Pinacate and Gran Desierto de Altar Biosphere Reserve) with its distinctive volcanic cones, craters and lava flows. For more details, see The landforms of the El Pinacate and Gran Desierto de Altar Biosphere Reserve.

The landforms of the Chihuahuan Desert have been molded by tectonic uplift and erosion. Steep-sided but low hills are separated by wide bajadas from former lake beds and alluvial plains, occupying inland basins known as bolsons. Many parts form closed, interior basins with no external drainage. South of Ciudad Juárez, at Samalayuca, is one of Mexico’s most extensive areas of sand dunes. This is one of the most arid parts of the country, with high levels of salinization.

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Apr 032014
 

Geo-Mexico agrees entirely with Joseph Kerski (a key member of ESRI’s Education Team), that it is amazing “how little American students really know about their neighbor to the south.” In order to help remedy this situation, ESRI’s Witold Fraczek has created a series of online “story maps” about Mexico. The maps can be accessed in several different ways, including as an ArcGIS Online presentation and an iPad iBook, or via this webpage.

The six stories are entitled:

Each “story” includes several maps (covering topics such as population, landforms, climate, historical landmarks, caves, indigenous cultures, tourist attractions), some of which are interactive in the sense that clicking on a marked point brings up a pop-up panel with a photograph and/or additional information about that place. The maps, linked by short commentary notes, can be viewed at a variety of scales.

This series of maps has many strong points, and could certainly be useful in some geography classes, but it also has some weaknesses that should be taken into account when using them. Brief comments follow on each of the six stories.

1 Explore Mexico (Crime vs. Tourism)

The first map in this mini-series depicts “tourism attraction density” based on “650 major points of interest”. No clues are offered as to how the 650 points were selected, and indeed, some can not really be shown by points on a map since they cover larger areas. The map appears to weight all 650 points equally, though some are major, major tourist attractions (like the pyramids of Teotihuacan) that attract thousands of visitors a day, while others are very much less significant.

The second map, showing the “20 cities with most murders” uses data from 2011 (now out-dated) to conclude that “crime, measured by the total number of murders” appears to be “spatially isolated from the areas most attractive to tourists”. Surely murder rates (per 100,000 people) are a better measure than the number of murders in each city?

Murder rate per 100,000 is used as the basis for comparing Mexico with its regional neighbors, but Mexico is so large (and the murder rates across the country so varied) that comparisons at this scale mean relatively little, especially when some of the nations are tiny Caribbean islands, where one or two murders extra in any year can mean a significant spike in their murder rate.

2. Mexico’s Natural Wonders

The introductory text to this section rightly highlights how “the natural world of Mexico varies amazingly, from tropical jungles and coral reefs to deserts and glaciers.”

However, the statement that “Central Mexico is home to billions of Monarch Butterflies, whose 2 year /4 generation long trip to Canada and back amazes both scientists and the general public” is misleading. First, there may be millions of Monarch Butterflies, but there are not billions. Secondly, not all Monarch Butterflies migrate. Thirdly, those that do migrate are part of an annual (1 year) cycle involving 4 or 5 generations, not a two year cycle.

The text later claims that the Monarch Butterfly reserves “are located on old volcanic hills covered with pine-oak forest”. Actually, they overwinter in pine-fir forests. Mexico’s pine-oak woodlands occur only at much lower elevations.

The only birds incorporated into Mexico’s “biological wonders” are its pink flamingos, yet there are dozens of other bird species that are equally worthy of inclusion. Fortunately, the texts accompanying the maps of caves and cenotes (sinkholes), waterfalls, volcanoes, canyons and geologic sites appear to be much more accurate.

Screenshot from ESRI's story maps of Mexico.

Screenshot of ESRI’s story maps of Mexico.

3. Historical monuments

This section includes a useful map of Mexico’s World Heritage sites, though absent (from both the declared sites and the proposed sites) is the El Pinacate and Gran Desierto de Altar Biosphere Reserve in Sonora, which in June 2013 became Mexico’s 32nd World Heritage Site.

The great weakness of the maps of “archaeological sites” and “missions and monasteries” is that no clues are given as to how and why particular locations were selected for inclusion. This leads to some anomalies in the distribution. For example, Oaxaca is almost a no-show for “missions and monasteries” according to the map, despite such buildings being the subject of an excellent and extensive book by Richard Perry published as long ago as 2006, Exploring Colonial Oaxaca: The Art and Architecture.

The map of Magic Towns is also a useful map, though many more towns have been added to the list since 2012.

4. Geography of Mexico – Did You Know?

This series of maps will be quite useful to many classes as a quick way to introduce the basic physical and settlement geography of the country. Maps of relief and precipitation are accompanied by one of time zones and a simple map of states (though these are not named on the “map story” version) and major cities.

The introductory text to this section claims that “the array of Mexican volcanoes stretches along the same latitude as the volcanoes of Hawaii. Analogously, those located at the eastern ends are the newest and highest.” This may be true for Hawaii, but is not the case for Mexico. There is no simple pattern to the heights of Mexico’s major volcanoes, and certainly those in the east are not significantly younger than those in the west.

5. Indigenous People of Mexico

The single map in this section attempts to show the location of about 25 of Mexico’s many indigenous groups. The colors chosen for each group are in many cases confusingly similar, though the names of each group do appear as you zoom in on parts of the map.

The introductory text makes a strong case for Mexico’s attractiveness to tourists, yet concludes with the strange (and unanswered) question, “So why isn’t Mexico a major tourist destination?” Mexicans would beg to differ. Mexico is a major tourist destination. In 2013, for example, it received 23.7 million international visitors who spent 13.8 billion dollars. In fact, Mexico is ranked #11 in the world in terms of tourist arrivals (and that number excludes the 70 million or so border tourists each year).

6. Cartograms of Mexico

The cartograms in the last section certainly add interest to the map stories, but the basis of the “travelers attractiveness” map (those 650 tourist attractions again) means that the map is not a very good reflection of tourist numbers across the country. The significance of the State of Mexico is greatly exaggerated, while states such as Quintana Roo (with the resort of Cancún) and Baja California Sur (with Los Cabos) fail to stand out.

The final “fictional map” purports to portray Mexico as perceived by Californians. Based on the author’s personal impressions, in some ways this is the single most interesting map in the entire collection!

All in all, these maps are a mixed bag. The idea behind them is great, as is the decision to produce them in a flexible GIS system. If the details were refined a little, and more explanation offered about the basis for selecting places for inclusion, they would be even more useful in geography classes, and might go some way towards helping American students gain a better appreciation for their southern neighbor.

Why is northern Mexico a desert region?

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Oct 102013
 

Much of northern Mexico experiences either an arid (desert) climate (less than 250 mm [10 in] of rain/year) or a semiarid (semi-desert) climate (250–750 mm [10–30 in] of rain/year). Areas with an arid (desert) climate (see map) include most of Baja California and western Sonora (together comprising the Sonoran desert), as well as the northern section of the Central Plateau (the Chihuahuan desert). These areas can experience frost and freezing during the winter.

Major climate regions in Mexico. (Fig 4-5 of Geo-Mexico, the geography and dynamics of modern Mexico). All rights reserved.

Major climate regions in Mexico. (Fig 4-5 of Geo-Mexico, the geography and dynamics of modern Mexico). All rights reserved.

Areas of semiarid (dry steppe) climate include most of the Central Plateau as well as western sections of the Western Sierra Madre, northern Yucatán and scattered inland areas as far south as Oaxaca. The rains in this region fall mostly in the summer, and localized heavy thunderstorms are quite common. The southern parts of this climatic region are warmer than the northern parts. (Mexico’s seven climate regions)

Why do parts of northern Mexico receive very little precipitation, making them deserts?

The major reason is that the zone between the Tropic of Cancer (latitude 23.5 degrees N) and latitude 30 degrees N is influenced by the Hadley Cell. This is the name given to the atmospheric circulation in tropical regions, named after George Hadley, the English amateur meteorologist who first proposed its existence, in 1735.

The Hadley Cell

The functioning of the Hadley Cell

The Hadley Cell is the driving force behind many aspects of Mexico’s weather and climate. How does it operate? Solar heating is at a maximum near the equator and diminishes towards the poles. The area near the equator is the Intertropical Convergence Zone or ITCZ (see diagram). The heating of the ITCZ makes the air there rise, leaving an area of low pressure on the surface. This low pressure sucks in air along the earth’s surface from the subtropical high pressure areas about 30 degrees N and S of the equator creating the trade winds. The trade winds pick up moisture and latent heat over the oceans before converging from either side of the equator in the ITCZ. As the air in the ITCZ rises vertically, its water vapor condenses and rain falls from the towering convective clouds. This is the ascending limb of the Hadley cell. At a height of 10–15 km above the surface, the air, now minus its moisture, returns polewards as high level anti-trade winds. Sunbathers on Mexican beaches who notice two sets of clouds above them at different heights traveling in opposite directions are witnessing the trade winds and anti-trade winds in action.

In the subtropics, this air then descends again towards the surface to complete the cell and initiates the surface trade winds again. The descending air warms up as it sinks; its relative humidity decreases, and so no precipitation occurs; hence these high pressure subtropical areas are arid. Mexico’s arid and semiarid areas coincide with the descending air segment of the Hadley Cell and these high pressure subtropical areas.

In addition, the climate of the west coast of the Baja California Peninsula is influenced by the cool Californian current, which flows towards the south. The relative humidity of the air above it drops as the current enters warmer waters, so it is not likely to bring rain to the peninsula.

The aridity of the Sonoran desert is also partly due to its position in the rain shadow of the Western Sierra Madre. The Chihuahuan desert is in an even more marked rain shadow, protected by both the Western Sierra Madre and the Eastern Sierra Madre.

Stunning stream patterns in northern Baja California

Photographer Adriana Franco from Querétaro has taken several truly stunning artistic images of stream patterns in the semi-arid region of northern Baja California (near Mexicali). The photos, taken from an ultralight, show the details of the dendritic (= tree-like) stream patterns in this region. Dendritic stream patterns are common worldwide, but these images are exceptional. In general, dendritic stream patterns are associated with relatively gentle gradients where the underlying rocks are similar throughout the drainage basin.

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The three main causes of precipitation in Mexico

 Excerpts from Geo-Mexico  Comments Off on The three main causes of precipitation in Mexico
Jul 222013
 

The three basic types of rainfall (convectional, orographic and cyclonic) all play a role in determining the amount and timing of precipitation in Mexico.

Why does it rain?

In Mexico, most precipitation falls as rain, though snowfalls are not uncommon in parts of northern Mexico or at the highest elevations where air temperatures are cooler. For precipitation to occur, the air must first acquire moisture. Warm air absorbs water through evaporation from nearby bodies of water and through evapotranspiration from plants. The amount of water the air holds compared to the maximum amount it can hold at that temperature is the relative humidity. If warm moist air rises, it will cool. As it cools, its relative humidity rises. If relative humidity reaches 100% and condensation nuclei (particles such as dust or contaminants) are present, then water vapor will condense out of the air to form clouds. As clouds develop, water molecules coalesce until individual drops are heavy enough to fall out of the cloud as precipitation. Ice crystals fall as snow, water falls as raindrops, frozen ice pellets fall as hail.

For precipitation to occur, the weight of the individual drops must be sufficient for the effects of gravity to overcome the upwards thrust of the surrounding air. In very unstable conditions where air is rising rapidly, individual raindrops must become much larger before they can fall out of the cloud. The largest raindrops will have traveled up and down inside the cloud repeatedly, gaining size, before they finally fall to the ground. The same principle applies to hailstorms which gather an additional layer of ice for every trip they make inside the cloud before falling.

Though Mexico is considered to be relatively arid, the country as a whole receives an average of about 760 mm (30 in) of rain per year. This is a considerable amount of precipitation, almost exactly the same amount as Toronto, and considerably more than the average for either Canada or the USA.

Annual precipitation in Mexico (Fig .4.3 of Geo-Mexico)

Annual precipitation in Mexico (Fig .4.3 of Geo-Mexico, the geography and dynamics of modern Mexico) All rights reserved.

The three main causes of precipitation in Mexico

Convectional rain is associated with hot afternoons. During the morning, warm air near the surface collects great quantities of moisture. As temperatures increase towards mid-day, pockets of moist warm air are sent upwards, quickly leading to condensation and clouds. As the clouds continue to rise, they cool to the point where precipitation becomes inevitable. Afternoon and evening rain showers result, often heavy and accompanied by thunder and lightening. Convectional rain occurs throughout Mexico but is a summer phenomenon since this is the time of year when solar radiation and ground heating is at a maximum. The effects of convectional rain are enhanced by the presence at that time of year over southern Mexico of the Intertropical Convergence Zone, a broad belt of generally rising air which migrates seasonally either side of the equator.

Orographic rainfall, the second type of rainfall, is associated with mountains. Mountains block the movement of clouds and force them to rise. This has a profound impact on precipitation. As the clouds rise, further condensation occurs and precipitation becomes extremely likely, as they cool to the point where they can no longer hold their moisture. Therefore, it rains a great deal on the windward or wet side of the range. By the time the air passes over the mountain range to the other side, it has lost much of its moisture. As it descends, it warms up and its relative humidity falls, so that there is little chance of any precipitation on the leeward side, known as the rain shadow.

For example, the summer north-east trade winds blow moist clouds from the Gulf of Mexico towards the Southern Sierra Madre and Chiapas Highlands. The eastern side of these mountains receives heavy rainfall. The mountain slopes in central Veracruz, eastern Oaxaca and parts of Chiapas have about 150 cloudy days and get about 2000 mm (80 in) of rain a year. However, the western slopes get only half as much rain and have only 90 cloudy days a year. Orographic precipitation sets virtually all the rainfall and snowfall records, even more than hurricanes. Tenango, Oaxaca is the rainiest place in Mexico; it receives about 5000 mm (16.4 ft) of rain each year. The orientation of mountain ranges is therefore critical to understanding precipitation patterns. The differences between windward and leeward sides of a mountain range can be very dramatic. For instance, El Chico and Pachuca in the state of Hidalgo are only 10 km apart but have 1500 and 400 mm of precipitation respectively each year.

The third type of rainfall is called cyclonic or frontal precipitation. This is the form of precipitation brought by the mid-latitude storms known as nortes, and the tropical storms that sometimes evolve into hurricanes. Nortes occur when the polar air behind a cold front displaces the warmer surface air, forcing it to rise as the cool air pushes its way underneath. At the surface, a sudden drop in temperature and the advent of cold winds marks the passage of the front, followed by several days of overcast skies with light rains or drizzle, onomatopoeically called chipichipis in some areas of Mexico.

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May 132013
 

Mexican rivers are not well suited for navigation and thus have had only a minor influence on Mexico’s historical development. Their most important use has been as sources of irrigation water and hydroelectric power. Mexico’s annual flow of river water (roughly 410 km3) is about 25% more than the St. Lawrence River, but 25% less than the Mississippi River. Most of this flow is in southern Mexico which gets by far the most rainfall. Mexico’s dams have an installed capacity of about 11 gigawatts of electricity, roughly one fifth of the country’s total generating capacity; they don’t operate at full capacity, so they only generate about one eighth of total electricity. Only about a fifth of the total river water is consumed for other productive purposes. This proportion is far higher for rivers in drier northern Mexico where river flow is significantly smaller during the dry winter months.

Fig 6-3 of Geo-Mexico: Rivers of Mexico

Fig 6-3 of Geo-Mexico: Rivers of Mexico; all rights reserved

The two longest rivers in Mexico, the Rio Bravo (Rio Grande north of the border) and Colorado, start in the US state of Colorado (see map). The Río Bravo is about 3000 km (1900 mi) long and forms the border between Mexico and the USA for about 2000 km (1250 mi). Occasionally floods shift its location resulting in border disputes. Though it drains about a quarter of Mexico’s total area, its drainage basin is arid and its total flow is less than 2% of Mexico’s total. The Colorado River, which is almost entirely in the USA, formed a vast delta in the otherwise arid Sonoran desert in northern Mexico. The amount of water reaching Mexico has declined dramatically as a result of the Hoover and Glen Canyon dams and other diversions in the USA (see here, here and here). As a result delta wetlands have been reduced to about 5% of their original extent, and the potential water supply for the rapidly-growing urban centers of Mexicali, Tijuana, Tecate and Rosarito has been compromised.

Interestingly, the Mexican river with the greatest flow, the Grijalva–Usumacinta, does not start in Mexico either (see map). The river has a double name because it is actually a double river, with two branches of similar length which both start in Guatemala. Each branch flows about 750 km (465 mi) through Chiapas before they unite in Tabasco about 25 km from the Gulf of Mexico. Each of the two branches has a flow of about 14% of Mexico’s total. The flow of the combined Grijalva–Usumacinta River is about twice that of the Missouri River in the USA.

There are several other important Mexican rivers. The Lerma River starts in the State of Mexico and flows westward into Lake Chapala and continues to the Pacific Ocean with the name Santiago. The Lerma–Santiago River system is about 1280 km (800 mi) long, the longest river entirely in Mexico. It drains about 6% of Mexico. The Lerma–Santiago, which flows through several states, is one of the economically most important rivers in Mexico because it feeds some of the country’s prime agricultural areas as well as the two largest metropolitan areas: Mexico City and Guadalajara. However, its flow is quite small, only about 2% of the national total.

The flow of the Balsas River, south of the Lerma–Santiago, is about three times that of the Lerma–Santiago. Though it offers some white-water rafting and irrigation opportunities, it is not as important economically. There are numerous rather long rivers that also flow west to the Pacific from the Western Sierra Madre in northwestern Mexico, but these have relatively little water. There are also several rather long rivers in the north such as the Nazas that flow into landlocked basins and either die or feed small drying lakes.

Three major rivers flow into the Gulf of Mexico through the state of Veracruz. The Rivers Papaloapan and Coatzacoalcos start in Oaxaca and flow through southern Veracruz. Their combined flow is nearly 20% of the national total. The Pánuco–Tamesi–Moctezuma River system starts in the State of Mexico and carries nearly 5% to the Gulf of Mexico at Tampico.

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The seven main canyons in the Copper Canyon region

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Jul 302012
 

The Copper Canyon region in Mexico is the informal name for the area, in the south-west part of Chihuahua state, where several deep canyons bisect the Sierra Tarahumara. The 10,000 km2 area, part of the Western Sierra Madre, is home to about 50,000 Tarahumara Indians, one of the largest native Indian groups in North America. While generally referred to in English as the Tarahumara, the people’s own name for themselves is Raramuri“, literally “the light‑footed ones” or “footrunners”.

Location of Barrancas del Cobre (Copper Canyon region)

Location of Barrancas del Cobre (Copper Canyon region)

While the Tarahumara have so far succeeded in keeping many aspects of their distinctive culture relatively unadulterated, the pressures on them have increased considerably in recent years as improving highway links have made the region more accessible, not only to tourists, but also to developers looking to exploit the region’s forest and mineral resources.

Spanish-speakers usually refer to this region as the “Barrancas del Cobre” (Copper Canyons, plural). The table shows the seven main canyons, only one of which, strictly speaking, is the Copper Canyon. The precise number of canyons depends on whether they are defined by rivers or by local names since different stretches of canyon along a single river have sometimes been given different names.

Canyon Elevation at the rim (meters / feet a.s.l.) Elevation of stream in canyon floor (meters / feet) Depth (meters/feet)
Canyons south and east of railroad
Urique (south of Urique village) 2370 / 7775 500 / 1640 1870 / 6135
Sinforosa (Río Verde) 2530 / 8300 700 / 2300 1830 / 6000
Batopilas 2500 / 8200 700 / 2300 1800 / 5900
Urique (mid-point, aka Copper Canyon) 2300 /7545 1000 / 3280 1300 / 4265
Canyons north and west of railroad
Candameña (below Basaseachi Falls) 2540 / 8330 900 / 2950 1640 /5380
Chinipas 2000 / 6560 400 / 1310 1600 / 5250
Oteros 2220 / 7280 700 / 2300 1520 / 5980

The major canyon is the Urique Canyon. This is the one seen by most tourists because it is the closest to the railway line that traverses the region. Both the Urique River and the Batopilas River flow into the River Fuerte, which enters the Gulf of Mexico near Los Mochis.

Tarahumara place names

The Tarahumara have very few place-names. They do not usually have identifying names for specific mountains, streams, trails or landmarks , but do give names to every small settlement, even if it only consists of two or three homes.  These names serve to distinguish one family from another, but a single family may have several farms, each with a different name. The Tarahumara do have “a rather complete terminology for plants, animals, and birds.”  [Bennet & Zingg, 1935] The place-names for settlements are usually two-part names, consisting of a descriptive name plus a place suffix.

Examples include:

  • Aworítci, from aworíki, “cedar tree” (tci gives idea of a grove of trees).
  • Wisarótici, from wisaró, “poplar tree.”
  • Tcimétabo, from tcimáka, “leather money bag”, plus –tabo, place-ending.
  • Wagítali, from wagítci, “dead tree.”
  • Garitcí, from garíki, “house.”
  • Kusárare, from kusáka, “eagle.”

In future posts, we will delve further into the geography of the  Copper Canyon region and the lifestyle of the Tarahumara Indians.

Sources:

Bennett, W. and Zingg, R. (1935) The Tarahumara. Univ. of Chicago Press. Reprinted by Rio Grande Press, 1976. Classic anthropological work.

Gajdusek, D.C. (1953) “The Sierra Tarahumara” in Geographical Review, New York. 43: 15‑38

Schmidt, R.H. (1973) A Geographical Survey of Chihuahua, monograph #37 Texas Western Press.

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Is Mexico the world’s 13th or 14th largest country?

 Other  Comments Off on Is Mexico the world’s 13th or 14th largest country?
Jul 022012
 

One would think that with satellite imagery there would be no question concerning the land area of countries. However, when talking about area there are some definitional issues. Are we talking about “land area” or “total area” which includes land area and inland water bodies such as lakes, reservoirs and rivers? This can be important when talking about the relative size of countries.

Without question Russia is the largest with nearly twice the area of the second place country. What are the second, third and fourth place countries? If we are talking about “land area”, excluding inland waters, then China is second (9.570 million square kilometers), the USA is third (9.162m sq km) and Canada is fourth (9.094m sq km). However, when inland waters are included to get “total area” then Canada is second (9.985m sq km), China is third (9.597m sq km) and the USA is fourth (9.526m sq km). Generally “total area” is the measure used to compare the geographic areas of countries (see table).

Total area of the world’s largest countries (millions of square kilometers)

RankCountryArea (millions of sq. km) RankCountryArea (millions of sq. km)
1Russia17.09811Congo2.345
2Canada9.98512Saudi Arabia2.150
3China9.59713Mexico1.964
4USA9.52614Indonesia1.911
5Brazil8.51515Sudan (post 2011)1.861
6Australia7.69216Libya1.759
7India3.16617Iran1.648
8Argentina2.78018Mongolia1.564
9Kazakhstan2.72519Peru1.285
10Algeria2.381

Generally we might expect a country’s geographic area rank to stay the same from year to year and even decade to decade. However, this is not the case. Prior to 1991 Mexico was considered the world’s 13th largest country. However with the dissolution of the Soviet Union in 2011, Kazakhstan became an independent country ranked 9th in total area. This pushed Mexico down to 14th.

When South Sudan split away from Sudan in mid 2011, the area of “new” Sudan was reduced by over 25%. This dropped Sudan from 10th to 15th on the list of the world’s largest countries. It also moved Mexico from 14th back up to 13th place on the list. Such political changes can have enormous impact on the size of countries. For example, prior to 1951 when Tibet was considered an independent country, the size of China was an eighth smaller than it is now. Mexico before 1846 was almost twice its current size and perhaps the fifth largest independent country behind only Russia, China, the USA and Brazil.

Another issue concerns whether Greenland (2.166m sq km)  is counted as a country. While Greenland is officially a dependency of Denmark it has been moving toward independence. In 1985 it left the European Economic Community (EEC) while Denmark remained in the EEC. Greenland has its own Parliament and Prime Minister; in June 2009 Greenland assumed self-determination with Greenlandic as its sole official language. If/when Greenland becomes officially an independent “country” it will be the world’s 12th largest, bumping Mexico back into 14th place. Until this happens, Mexico remains the world’s 13th largest country.

The changes in rank discussed above came about for political reasons. They did not involve any physical changes. With global warming and rising sea levels some countries will actually become geographically smaller. However these changes will not affect the area ranking of the 20 largest countries for at least the next hundred years.

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Subsidence incident leads to demolition of 31 homes in the State of Mexico

 Mexico's geography in the Press  Comments Off on Subsidence incident leads to demolition of 31 homes in the State of Mexico
Nov 302010
 

Thirty-one homes have been demolished due to structural damage resulting from subsidence in the colonia Benito Juárez. The subsidence, on 28 October 2010, occurred close to the Neza II garbage tip and affected more than 200 homes in total.

Temporary accommodation has been found for the families affected, who will have their rents of up to 2,000 pesos a month paid for the first six months. The compensation to be paid to the affected families from government coffers is still being decided.

Geologists and engineers from the Universidad Nacional Autónoma de Mexico (UNAM) y el Instituto Politécnico Nacional (IPN), are currently assessing the risks of alternative sites for rebuilding the 31 homes. Several areas of Nezahualcóyotl are known to be vulnerable to subsidence or to the sudden appearance of surface cracks (superficial faults).

The subsidence is presumed to have occurred because of the filtration of liquids from the Neza II tip through the subsoil, though precise details are still being investigated. To prevent further problems in the area, pipes are being installed to channel all liquid residues away from homes, and vents are being placed to allow the escape of gases emanating from within the garbage tip.

The three settlements of Nezahualcóyotl, Chimalhuacán and Los Reyes La Paz add about 1,000 tons of garbage daily to the Neza II tip. Authorities are now planning to close the tip completely by the end of November 2010.

Elsewhere in Nezahualcóyotl, the structural integrity of a shopping center and sports complex located near the Neza I tip are also being investigated.

The fact that subsidence occurs far more frequently in the eastern part of Mexico City (including Nezahualcóyotl) than elsewhere does not indicate that the solutions must be local. Ramón Aguirre, the director of Mexico City’s Water System (Sistema de Aguas de la Ciudad de México), has repeatedly emphasized the importance of looking at Mexico City’s potable water and drainage problems in the context of the entire metropolitan area (which extends well beyond the boundary of the Federal District). Aguirre fears that climate change and further over-exploitation of the aquifers, which Mexico City shares with the State of México, will only lead to more problems of water supply and more cases of subsidence.

Chapter 23 of Geo-Mexico: the geography and dynamics of modern Mexico looks at urban issues, problems and trends. To preview more parts of the book, click here and use amazon.com’s “Look Inside” feature.