Nevado Sajama

Nevado Sajama is the highest peak in Bolivia. It is an extinct volcano located in the Sajama Province of the Oruro Department. This massive mountain sits within the Western Andes on the western side of the Altiplano plateau. It is a composite volcano, which means it is made of several different volcanic structures. Specifically, a large stratovolcano sits on top of several lava domes. A stratovolcano is built from alternating layers of lava flows and pyroclastic material. This material radiates outward from the center of the mountain.

To understand how this mountain formed, we must look deep beneath the Earth. Sajama is part of the Central Volcanic Zone of the Andes. Volcanism here is triggered by a process called subduction. This occurs when the Nazca Plate moves beneath the South America Plate. As these plates interact, they trigger volcanic activity in the region. In the Oligocene epoch, changes in this subduction regime increased volcanic activity. The mountain grew on top of much older ignimbrites. Large faults in the Earth's crust also helped control where the volcanoes grew.

The geology of the mountain is quite complex. The main stratovolcano is composed of andesite rocks. These rocks contain minerals like hornblende, pyroxene, and olivine. The volcano erupted different types of rocks, ranging from andesite to rhyodacite. These rocks formed through processes like magma mixing and fractional crystallization. There are also parasitic vents located southeast of the main peak. These vents are smaller openings that produced their own lava domes and flows. These vents are older and seem to follow radial dikes, or underground rock structures.

Scientists use various methods to study the age of this volcanic landscape. One technique is called argon-argon dating. This method helped scientists determine that Sajama is approximately 679,000 years old. Other nearby lavas, known as the Kkota Kkotani lavas, are much younger. They date back to between 80,900 and 25,000 years ago. While the exact date of the last eruption is unknown, it likely happened during the Pleistocene or Holocene epochs. Even though it is extinct, geothermal heat remains. Hot springs on the Junthuma River reach temperatures of about 25°C.

The environment on Nevado Sajama changes as you climb higher. The summit is covered by a continuous ice cap. This ice makes the summit crater appear as a flat plateau. Below the ice, glaciers have carved deep valleys into the mountain. The terrain also features rock glaciers and moraines. Moraines are piles of debris left behind by moving glaciers. These moraines show different colors depending on the rocks they contain. At lower levels, you will find lava flows, matorral vegetation, and grasslands.

Nevado Sajama is home to a very special ecosystem. It features the highest treeline on Earth. This is where the Polylepis tarapacana trees grow. These trees form small woodlands in spots where water is available. Because of the high altitude, the trees are usually no taller than 5 meters. The mountain also has bofedales, which are high-altitude peat bogs. These wet areas support plants like Distichia and various grasses. Animals such as vicuñas, vizcachas, and mice live in these diverse habitats.

Human history is deeply tied to this mountain. Local communities consider Sajama a sacred site. Many oral traditions and myths describe the mountain as a living being. For example, one myth says Sajama is the head of the Mururata mountain. There are also about 40 archaeological sites found at lower elevations. These include chullpa burials and pukara fortifications. These sites show that people have used the mountain for many centuries. Today, the mountain is so famous that it appears on the 50-boliviano banknote.