Vilama (caldera) facts for kids

Vilama is a huge, ancient volcano crater (called a caldera) located on the border between Bolivia and Argentina. It formed during the Miocene epoch, which was millions of years ago. Vilama is part of a chain of volcanoes in the Andes mountains, known as the Central Volcanic Zone.

This area is very remote and is home to many large calderas and flows of hot ash and rock called ignimbrites. These volcanoes have been active for about 8 million years, and some of them were even supervolcanoes, meaning they had incredibly powerful eruptions.

The Vilama caldera is mostly hidden under younger volcanoes that have grown up around its edges. Its size is estimated to be between 15-18 kilometers (about 9-11 miles) and 35-40 kilometers (about 22-25 miles) wide. Lakes have also formed inside the caldera, and it has a raised area in the middle called a resurgent dome.

Vilama is famous for creating the enormous Vilama ignimbrite. This huge flow of hot ash and rock was released during a massive eruption about 8.4–8.5 million years ago. This eruption was so big that it had a volcanic explosivity index of 8, making it a supereruption. A lot of the ignimbrite stayed inside the caldera, but the part that flowed out covered more than 4,000 square kilometers (about 1,500 square miles). The total amount of rock and ash from this eruption was about 1,200 to 1,800 cubic kilometers (290-430 cubic miles), possibly even up to 2,100 cubic kilometers (500 cubic miles)!

Where is Vilama?

The Vilama caldera sits on the border between Argentina and Bolivia. It's in a high, flat area of the Andes mountains called the Puna-Altiplano. This region is mostly empty because of its harsh weather. However, people have found old archaeological sites here. Tools made from obsidian (a type of volcanic glass) from Vilama have been found far away in northwestern Argentina.

Vilama is part of the Central Volcanic Zone, which is one of four main volcanic areas along the Andes. This zone has over a thousand volcanoes! Many of these are tall, cone-shaped volcanoes called stratovolcanoes, like Coropuna and Ojos del Salado. They often reach heights of over 6,000 meters (about 20,000 feet). The Central Volcanic Zone also has many other large calderas, like Pastos Grandes and La Pacana.

How Big is the Vilama Crater?

The Vilama caldera is between 15-18 kilometers (9-11 miles) and 35-40 kilometers (22-25 miles) wide. Most of its edges are hidden by newer volcanic rocks. But on its western side, there's a steep cliff, 250-400 meters (820-1,300 feet) high, that shows where the caldera rim is.

Inside the caldera, there's a large, raised area called a resurgent dome, which is about 30 by 10 kilometers (19 by 6 miles). This dome is surrounded by a deep ditch, 400-800 meters (1,300-2,600 feet) deep, called a moat. This moat holds several lakes, such as Laguna Chojllas, Laguna Coruto, and Laguna de Vilama. The caldera gets its name from Laguna de Vilama.

Many younger volcanoes are found around the caldera. These include the Khastor domes, Cerro Alcoak, Cerro Salle, and the 5,678-meter (18,629-foot) high Vilama stratovolcano. These are mostly dacitic volcanoes, which means they formed after the main caldera collapsed.

How Vilama Formed

Off the western coast of South America, the Nazca Plate is slowly sliding underneath the South America Plate. This process is called subduction. It's been happening for millions of years and causes the volcanoes in the Andes to form. When the oceanic plate sinks, it heats up and releases water. This water helps rock melt in the layer above, creating magma that fuels the volcanoes.

East of the main volcanic chain, there's another area that has been volcanically active for a long time. This area has everything from small, single-eruption volcanoes to huge calderas with their ignimbrites. This region is called the Altiplano-Puna volcanic complex. It's one of the largest areas in the world with so many ignimbrite-producing volcanoes. These volcanoes were most active between 8 and 4 million years ago, with huge eruptions at places like Cerro Panizos, Coranzulí, Vilama, and La Pacana.

Scientists think that volcanic activity in this area started about 10 million years ago and really picked up 8 million years ago. This might have happened when hot, liquid rock (magma) from deep inside the Earth entered the Earth's crust. Even today, there are signs that volcanic activity is still happening, like ground movement at Uturunku. Scientists have also found a large body of partially melted rock deep under the Altiplano-Puna volcanic complex.

The ground before the Vilama caldera formed was made of different types of rock, including old sedimentary and volcanic layers. Later, other volcanoes in the region added more volcanic rocks to the Vilama caldera area. Over millions of years, the whole region was pushed up, forming a high plateau that is about 4 kilometers (2.5 miles) high on average.

What is the Vilama Ignimbrite Made Of?

The Vilama ignimbrite is mostly made of a type of volcanic rock called dacite. This rock contains visible crystals (called phenocrysts) of minerals like biotite, hornblende, plagioclase, pyroxene, and quartz. It also has tiny amounts of other minerals like allanite and zircon.

Scientists believe that before the eruption, the magma was very hot, between 760-810 degrees Celsius (1,400-1,490 degrees Fahrenheit). The magma for Vilama and other volcanoes in the Altiplano-Puna volcanic complex might have come from a mix of melted rock from deep inside the Earth (the mantle) and melted rock from the Earth's crust.

Climate and Nature

A view from Laguna Vilama towards the Vilama stratovolcano, showing the typical landscape of the area.

The Vilama region has a dry climate. It gets only about 300 millimeters (12 inches) of rain each year. Temperatures are usually between 3-6 degrees Celsius (37-43 degrees Fahrenheit), but they can change a lot between day and night.

The plants here are mostly shrubs that grow in dry, open areas. Common plants include Festuca grasses, quenoa trees, tola bushes, Prosopis ferox (a type of mesquite), and yareta (a cushion-like plant). The volcanic areas themselves don't have much plant life. Most living things are found near water, where grasses like Oxychloe andina and Werneria pygmaea grow. You can also find different mammals and birds in the region, including flamingos that live near the lakes.

The Vilama Eruption

The Vilama caldera was formed during the eruption of the Vilama ignimbrite. This huge eruption happened about 8.4–8.5 million years ago. Scientists think the eruption started when the roof of the magma chamber (where magma is stored underground) broke apart. This caused a powerful release of hot ash and rock through new vents. Similar eruptions have happened at other calderas in the Altiplano-Puna region. This eruption might have been a Plinian eruption, which is a very explosive type of volcanic eruption.

The Vilama ignimbrite is often "welded," meaning the hot ash and rock fused together as it settled. It has a lot of crystals but not many rock fragments or pumice (light, frothy volcanic rock). The crystals in the ignimbrite can be up to 3-5 millimeters (0.1-0.2 inches) long.

Inside the caldera, the Vilama ignimbrite settled in several layers, usually 10-20 meters (33-66 feet) thick. Some layers are even 40-50 meters (130-160 feet) thick. Together, these layers are at least 400-700 meters (1,300-2,300 feet) thick. Outside the caldera, the ignimbrite formed two main layers. The lower layer is not as densely welded and contains more rock fragments and pumice. Its thickness varies from 7 meters (23 feet) to over 110 meters (360 feet). The upper layer is thicker and covers a larger area. It's usually 18-60 meters (59-200 feet) thick.

Scientists have also found that other ignimbrites, which were once thought to be separate, are actually part of the Vilama ignimbrite. These include the Capaderos ignimbrite and the Toloma ignimbrite. This means the Vilama ignimbrite covers an even larger area, about 4,000 square kilometers (1,500 square miles).

The total amount of rock and ash from the Vilama eruption is hard to measure because much of it is hidden. But it's estimated to be between 1,200-1,800 cubic kilometers (290-430 cubic miles), possibly up to 2,100 cubic kilometers (500 cubic miles). Because of its enormous size, the eruption that formed the Vilama caldera is considered a supereruption with a volcanic explosivity index of 8. This means Vilama caldera is a supervolcano!

Volcanic activity continued at Vilama even after the caldera collapsed. The magma system recovered quickly, leading to the formation of the resurgent dome in the middle of the caldera. Some of these younger volcanic activities include the Khastor domes (5-8.1 million years old) and the Vilama stratovolcano, which was active into the Pleistocene epoch (about 1.2 million to 900,000 years ago). Scientists have also found a hidden area beneath the caldera that might be a solidified magma body.

See also

In Spanish: Cerro Vilama para niños