Llullaillaco

Llullaillaco is made of layers of lava, ash and rock.

A newer cone sits on top of an older volcano.

NASA explains that Llullaillaco is a stratovolcano, made of alternating layers of hardened lava, solidified ash and rocks thrown out by earlier eruptions. It sits on top of an older volcano that collapsed about 150,000 years ago.

Geologists divide it into two parts: an older, worn-down volcano about 23 kilometers across, and a younger, well-preserved cone on its eastern side that forms today's summit. Thick, sticky lava flows formed shapes called coulées.

Llullaillaco is a stratovolcano of alternating layers of hardened lava, solidified ash and ejected rocks, sitting atop an older volcano that collapsed about 150,000 years ago; viscous lava flows formed coulées (NASA).

Gardeweg, Cornejo and Davidson (1984) describe two units: Llullaillaco I (Pleistocene, 1.5 ± 0.4 million years by K-Ar dating), 23 km across, with two moderately to deeply eroded cones and extensive lava flows, mainly to the west; and Llullaillaco II (Holocene), a small, well-preserved cone on the eastern part of Llullaillaco I that forms the present summit, with lava domes and channeled flows. Hornblende dacite is the main rock type.

Under Llullaillaco, the Earth's outer layer is very thick.

The volcano is quiet now, but it erupted in the 1800s.

A 1984 study by Chilean geologists says Llullaillaco is built on Paleozoic rocks, including granite-like rocks and marine and volcanic rock formations. Here the continental crust is up to 70 kilometers thick, and the chain of volcanoes lies 200 kilometers east of the Chile-Peru Trench.

The study found no signs of activity, but historical records tell of eruptions in the 1800s, so the geologists called it a latent, or sleeping, volcano.

Llullaillaco is built on a basement of Paleozoic rocks (granitoids and marine and volcanic formations). In this part of the Andes the continental crust is up to 70 km thick and the volcanic chain lies 200 km east of the Chile-Peru Trench (Gardeweg et al., 1984).

The study reported no current signs of activity, but historical records (Brüggen, 1950) of nineteenth-century eruptions led the authors to class it as a latent volcano. NASA gives 1877 as the last recorded eruption.

Llullaillaco stands at the edge of a very dry desert.

Guanacos and vicuñas live in the park nearby.

NASA says Llullaillaco lies on the eastern edge of the Atacama Desert, one of the driest places on Earth, where rain is rarely recorded in many parts. The land around it is mostly bare peaks and nearly white salt pans.

Pockets of plants grow where steep mountains stop fog and moisture collects. They feed plant-eating animals: guanacos and vicuñas live in Chile's Llullaillaco National Park, which stretches west and south of the volcano.

Llullaillaco lies along the eastern margin of the Atacama Desert, one of the driest places on Earth, where precipitation is rarely recorded in many parts (NASA). A Landsat 7 image of 4 February 2003 shows mostly bare peaks, nearly white salt pans south and west of the volcano and some snow and ice on its slopes.

Pockets of plants survive where steep mountains block fog and let moisture collect, feeding herbivores; Parque Nacional Llullaillaco, west and south of the volcano, is home to guanacos and vicuñas. The 1984 study noted yearly snowfields and small remnant glaciers.

People can get sick high up on mountains, so go up slowly.

If your head hurts high up, tell a grown-up and go down.

Llullaillaco rises to about 6,700 meters. The US Centers for Disease Control and Prevention (CDC) says the body can adjust to thin air up to about 5,200 meters, but it needs time. The CDC says children get altitude sickness as easily as adults. Its main sign is a headache.

The CDC says to go up slowly and avoid going "too high too fast". Altitude sickness gets better quickly by going down 300 meters or more.

The CDC Yellow Book notes that the body can adjust to moderate hypoxia up to about 5,200 m but needs time, and children are as susceptible to altitude illness as adults. Headache is the main symptom of acute mountain sickness.

Travelers should ascend gradually, avoiding going "too high too fast"; above 3,000 m, sleeping altitude should rise by no more than 500 m a day. Acute mountain sickness improves rapidly with a descent of 300 m or more.