The mystery of the Alarcon Rise

 Updates to Geo-Mexico  Comments Off on The mystery of the Alarcon Rise
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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Ecological footprints, marine conservation and Cancun’s underwater sculpture park

 Mexico's geography in the Press  Comments Off on Ecological footprints, marine conservation and Cancun’s underwater sculpture park
Feb 112013

The Global Ocean Commission, a new, high-level international effort to try to stave off eco-disaster in the world’s oceans, is being launched tomorrow in London, U.K.. Headed by former UK foreign secretary, David Miliband, former South African finance minister Trevor Manuel, and José María Figueres, a former president of Costa Rica, the Commission will promote international efforts to ensure the effective governance of international waters, and agreements governing such activities as deep sea fishing, pirate fishing, sea-floor mining and geo-engineering, all considered to be potential threats to the long-term viability of ocean ecosystems.

Miliband is quoted as saying that “We are living as if there are three or four planets instead of one, and you can’t get away with that.” Actually, the ecological footprint of the USA, as one example, is much closer to ten “global hectares per person” than three or four. (Each global hectare encompasses the average annual productivity of all biologically productive land and ocean areas in the world). The world’s biocapacity—the amount of resources its ecosystems can supply each year—is only equivalent to about 2 global hectares per person, a value that is declining each year as population increases (see Mexico’s ecological footprint compared to that of other countries).

2002 Postage Stamp: reef conservation

2002 Postage Stamp: reef conservation

Mexico is one of the six most biodiverse countries in the world. While it has taken many steps to protect its marine resources, by enacting legistlaiton establishing fishing restrictions and protected areas, much remains to be done. Mexico’s coral reefs are particularly vulnerable. For example, the Cancún Marine Park is one of the most visited stretches of water in the world with over 750,000 visitors each year, placing immense pressure on its resources. We described one unusual conservation effort related to this area in “Artificial reef near Cancún doubles as an underwater art gallery” [Mar 2012] which looked at the work of Artist Jason deCaires Taylor, who created an underwater sculpture park, the Underwater Art Museum (Museo Subaquatico de Arte, MUSA), near Cancún.

The museum, begun in 2009, currently consists of more than 450 permanent life-size sculptures set in the waters surrounding Cancún, Isla Mujeres and Punta Nizuc. Taylor is adding sixty additional underwater sculptures to the park, many of them modeled after local residents. This underwater museum is both attractive and functional, providing new habitat for coral and other marine life, as well as diverting snorkelers and divers away from fragile coral reefs, allowing them more chance to recover from the impacts of overuse.