El Pinacate y Gran Desierto de Altar Biosphere Reserve
El Pinacate y Gran Desierto de Altar Biosphere Reserve is a UNESCO World Heritage Site located in the Sonoran Desert of Sonora, Mexico, inscribed in 2013. This unique reserve encompasses volcanic landscapes, including the dormant Mt. Pinacate and approximately 400 single-eruption volcanoes, alongside dramatic geological formations such as maar craters and the largest sand sea in North America. The reserve is divided into two key areas: the Sierra Pinacate, known for its volcanic features, and the Sierra del Rosario, characterized by granite inselbergs and extensive aeolian dunes.
The region has a rich history of volcanic activity dating back over two million years, with evidence of human habitation going back at least ten thousand years, primarily by seminomadic groups. The reserve supports diverse ecosystems, housing over 540 plant species and various endangered species, including the Sonoran pronghorn antelope and the lesser long-nosed bat. However, it faces threats from invasive species, climate change, and development pressures. The biosphere reserve is significant not only for its natural beauty and geological importance but also as a vital habitat that preserves a portion of the Sonoran Desert.
El Pinacate y Gran Desierto de Altar Biosphere Reserve
Site information
- Official name: El Pinacate and Gran Desierto de Altar Biosphere Reserve
- Location: Sonora, Mexico
- Type: Natural
- Year of inscription: 2013
Located within the Sonoran Desert, this site protects unique and important geologic features in its two core areas. The Sierra Pinacate zone in the eastern part of the site includes the volcanic field around Mt. Pinacate, a four-thousand-foot dormant volcano with surrounding lava flows and ash layers from its history of eruptions. In addition, this area includes about four hundred single-eruption volcanoes with their associated lava flows and ten maar craters, created by interactions between molten rock and groundwater that resulted in violent explosions of steam. The Sierra del Rosario zone in the western part of the site includes granite inselbergs (isolated mountains) surrounded by aeolian (wind-driven) sand dunes, which form the largest erg (sand sea) in North America. The erg also features unusual "star dunes." This landscape is so forbidding that astronauts were sent there to train for the moon landing. The rugged, remote site is home to diverse communities of desert fauna and flora, including the endangered Sonoran pronghorn antelope. It is also significant as part of a much larger contiguous protected zone in Mexico and the United States which preserves almost 12 percent of the Sonoran Desert (7,515,221 acres).
History
Volcanic activity on the Sierra Pinacate site, which covers about six hundred square miles (1,500 square km), can be traced back more than two million years. The earliest identifiable series of eruptions ended around 1.2 million years ago, creating a volcano known as Volcán Santa Clara. Since then, additional lava flows have buried Volcán Santa Clara and created the current Sierra Pinacate, a shield volcano composed of layers of lava from one or a few magma chambers beneath the earth. It is surrounded by fields of lava, including tubes, pahoehoe (smooth lava), aa (jagged lava), and scoria (lava with internal bubbles). Some of the smaller surrounding volcanoes are made of lava from the vents of the old Volcán Santa Clara, while others have unique sources. The most recent eruptions in this area are thought to have been around two thousand years ago.
The ten maar craters are arranged in a semicircle in the northern part of the Pinacate field. There may be more of them to the west of the visible grouping, buried beneath the sand of the Altar desert. Evidence from ancient seeds and other materials suggests that the Gran Desierto has been a desert at least since the last glacial maximum, around 24,500 BCE.
Despite the forbidding terrain, groups of seminomadic foraging people began to occupy the region at least ten thousand years ago. The most recent indigenous inhabitants were the Hia Ced O'odham ("Sand Dune People"), whose creation stories are set in the Sierra Pinacate. By the end of the nineteenth century, they had shifted to a more settled way of life or joined other O'odham groups, and the descendants of the Hia Ced O'odham now live in Arizona among other O'odham peoples. It is believed that they were a very small group, perhaps a few hundred people, when they lived in the Sierra Pinacate and Altar desert region because of the extremely low carrying capacity of the fragile environment.
For outsiders, access to the area was very difficult until 1956, when a highway was opened at its northern boundary. Earlier attempts by Mexican pioneers to establish ranches or farms had failed because of lack of water. Hunting, small-scale ranching, mining, and timber harvesting did take place on the fringes of the site, leaving scars on the landscape which have been slow to recover. In 1979 the Mexican government established the first preserve in the area and followed this initiative with research to create a scientific basis for the establishment of the biosphere reserve, established in 1993. In 2013, UNESCO inscribed the biosphere reserve as a World Heritage Site. The site has maintained much of its wild character and is considered to be stable by the International Union for the Conservation of Nature and Natural Resources, although it is threatened by additional roads and powerlines, the arrival of invasive species, and climate change.
Significance
The biosphere reserve was inscribed as a World Heritage Site because of its natural beauty (Criterion vii), its geological significance (Criterion viii), and its significance as a natural habitat (Criterion x). From an aesthetic perspective, the outstanding features of the site include its dynamic sand dunes, the visual contrast of the dark lava fields and granite inselbergs with the light sand of the desert, and the ten enormous circular maar craters. The dunes, craters, and volcanic fields provide a unique resource for earth scientists and offer insights into the history of the planet.
The region's diverse geology has created a wide range of natural habitats, including the individual microhabitats of the craters, sky islands atop the peaks, the dunes and sand plains, areas of intermittent water flow, and even pozos (inland springs) in the western part of the reserve. It supports a wide range of animal and plant life, including species with very limited ranges and those isolated by the region's topography. The sky island atop Mt. Pinacate is home to species that occur nowhere else in Mexico, including plants that have not grown in the surrounding regions since the ice age and an isolated community of desert tortoises that lives in the bottom of the MacDougall crater. Threatened or endangered species include the Sonoran pronghorn antelope, of which fewer than five hundred survive, the lesser long-nosed bat, which rears its young at cave-based colonies within the reserve, and the desert pupfish, which is found only in some of the springs. Overall, the reserve supports over 540 known plant species, although fewer than 100 of them inhabit the desert, as well as at least 40 species of reptiles and amphibians, 44 mammal species, 4 species of fish, and more than 200 bird species.
Bibliography
Brenner, Jacob C., and John G. Davis. "Transboundary Conservation across Scales: A World-Regional Inventory and a Local Case Study from the United States-Mexico Border." Journal of the Southwest, vol. 54, no. 3, 2012, pp. 499–519.
"El Pinacate y Gran Desierto de Altar." National Park Service, 10 June 2023, www.nps.gov/orpi/planyourvisit/pinacate.htm. Accessed 5 Dec. 2024.
Felger, Richard Stephen, and Bill Broyles, editors. Dry Borders: Great Natural Reserves of the Sonoran Desert. U of Utah P, 2007.
Phillips, Steven J., and Patricia Wentworth Comus, editors. A Natural History of the Sonoran Desert. Arizona-Sonora Desert Museum Press/U of California P, 2000.
Martínez, David. "Hiding in the Shadows of History: Revitalizing Hia-Ced O'odham Peoplehood." Journal of the Southwest, vol. 55, no. 2, 2013, pp. 131–73.
Migoń, Piotr. "The Significance of Landforms: The Contribution of Geomorphology to the World Heritage Programme of UNESCO." Earth Surface Processes and Landforms vol. 39, no. 6, 2014, pp. 836–43.
El Pinacate and Gran Desierto de Altar Biosphere Reserve. World Heritage List. World Heritage Cultural Centre, UNESCO, 2016. HYPERLINK "http://whc.unesco.org/en/list/1410" whc.unesco.org/en/list/1410. Accessed 5 Dec. 2024.