San Pedro (Chile volcano) facts for kids
Quick facts for kids San Pedro |
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San Pedro with San Pablo volcano immediately right
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| Highest point | |
| Elevation | 6,155 m (20,194 ft) |
| Prominence | 2,034 m (6,673 ft) |
| Parent peak | Ojos del Salado |
| Listing | Ultra |
| Geography | |
 San Pedro
Location in Chile
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| Parent range | Andes |
| Geology | |
| Mountain type | Stratovolcano |
| Last eruption | 1960 |
| Climbing | |
| First ascent | 16 July 1903 George Courty & Filemón Morales |
San Pedro is a tall, active volcano in northern Chile. It is one of the highest active volcanoes in the world! This volcano is part of the Andes mountain range. It belongs to a group of volcanoes called the Central Volcanic Zone. This area also has other very tall volcanoes, like Ojos del Salado and Llullaillaco.
Like many volcanoes in the Andes, San Pedro formed because the Nazca Plate is sliding under the South American Plate. This process is called subduction. San Pedro has a neighbor volcano, San Pablo. San Pedro itself is made of two main parts, often called the "Old Cone" and the "Young Cone." These parts are made of different kinds of volcanic rocks.
The Old Cone was active over 100,000 years ago. A huge landslide later cut off its side. The Young Cone then grew in the space left by this landslide. San Pedro also had glaciers on it long ago. A very big eruption happened about 10,000 years ago. Some smaller eruptions have happened more recently. Today, the volcano still has fumaroles, which are vents that release steam and gases.
Contents
Where is San Pedro Volcano Located?
San Pedro volcano is in northern Chile. It's in a remote area with few people. The border with Bolivia is about 35 kilometers (22 miles) away. There are some small towns nearby, like Ascotán and Cupo. A railway station and roads are also close to the volcano.
San Pedro is part of the Central Volcanic Zone, which is about 600 kilometers (370 miles) long. This zone has about 44 active volcanoes in Chile. Many of these volcanoes are very tall, some reaching almost 7,000 meters (23,000 feet) high. Most of the volcanoes in this area are not very active today. They mainly show signs of activity through fumaroles, like San Pedro.
What Does San Pedro Volcano Look Like?
San Pedro is one of the tallest volcanoes on Earth. You can see it from far away, even from Calama, which is 85 kilometers (53 miles) distant. Its height is around 6,155 meters (20,194 feet) above sea level.
San Pedro is a composite volcano, which means it's built up by many layers of hardened lava and ash. It forms a twin volcano with San Pablo, which is about 6 kilometers (3.7 miles) to the east. San Pedro has an "Old Cone" to the east and a slightly lower "Young Cone" to the west. The Young Cone has two craters. Lava flows from one of these craters and has filled an older, wider crater.
The top of San Pedro has rocks changed by hot water and steam. There are also sulfur deposits there. People used to mine sulfur on the volcano until the 1930s.
How Lava Flows Shaped the Volcano
Many lava flows make up the volcano. The top part of the Young Cone is covered with these flows. They are very thick, up to 100 meters (330 feet) in some places. Down the sides of the volcano, especially on the northwest, lava flows spread out from the crater.
Landslides and Hot Avalanches
Scars on the volcano show where mudflows started. The largest mudflow covered a huge area, reaching the Loa River. These mudflows happened between 110,000 and 36,000 years ago.
Hot avalanche deposits, also called pyroclastic flows, are also found on the volcano. These are fast-moving currents of hot gas and volcanic debris. The largest one covers a big part of the volcano. These hot avalanches likely happened because the volcano's steep slopes made lava bodies unstable.
San Pedro also had a massive sector collapse. This is when a large part of the volcano's side breaks off and slides away. This collapse removed the northwestern side of the volcano. It created a huge debris field covering 120 square kilometers (46 square miles). This is similar to what happened at Mount St. Helens during its eruption in 1980.
Smaller Volcanoes Nearby
A smaller volcano called La Poruña is on the western side of San Pedro. It's a scoria cone, which is a small, steep-sided volcano made of loose volcanic rock. La Poruña is about 900 meters (3,000 feet) wide and 140 meters (460 feet) high. It has its own lava flows that stretch far from the cone.
There is also a lava dome on the southwestern side of San Pedro. This is another type of smaller volcanic vent. It has produced some of the largest lava flows on San Pedro, covering 19 square kilometers (7.3 square miles).
Past Glaciers on San Pedro
San Pedro had glaciers in the past. You can see signs of this, like moraines (piles of rock and dirt left by glaciers) above 4,400 meters (14,400 feet). This glaciation happened during the late Pleistocene ice age. Today, there are no glaciers on the mountain.
The San Pedro River flows near the volcano. Long ago, lava flows from San Pedro blocked the river, creating a lake that no longer exists.
How San Pedro Volcano Formed
The Nazca Plate is sliding under the South America Plate in this region. This movement causes the volcanic activity in the Andes. Chile is part of the Pacific Ring of Fire, which has many volcanoes. In Chile, there are about 2,000 volcanoes along a 4,500-kilometer (2,800-mile) stretch.
Volcanic activity in Chile has happened in two main periods. The second period started much more recently. In the San Pedro area, volcanic activity has moved around over time.
Volcanoes in a Line
Volcanoes in this part of Chile often form lines. One such line, about 65 kilometers (40 miles) long, includes San Pedro, Paniri, and Cerro Chao. The youngest volcano in these lines is usually the one farthest west.
The ground beneath San Pedro is made of older volcanic rocks. These include ignimbrites, which are deposits from fast-moving, hot volcanic flows.
What is San Pedro Made Of?
The rocks from the Old Cone are mostly andesite and basaltic andesite. The Young Cone has both andesite and dacite rocks. These rocks are part of a group called "potassium-rich calc-alkaline."
The volcanic rocks from San Pedro usually look glassy. They have tiny crystals inside them. The main minerals are plagioclase and pyroxene. Scientists think the magma that feeds the volcano formed from different types of magma mixing together deep underground.
What is the Climate Like Around San Pedro?
The area around San Pedro has a very dry climate. It doesn't rain much, usually less than 100 millimeters (4 inches) per year. This dryness has been going on for a very long time. However, there was a wetter period during the last ice age, between 17,000 and 11,000 years ago. During that time, glaciers grew larger.
Temperatures change a lot between day and night. They can drop as low as -25°C (-13°F) and rise to 25-30°C (77-86°F).
When Did San Pedro Volcano Erupt?
San Pedro formed in two main stages: the Old Cone and the Young Cone. The Old Cone was built by lava and ash. It was later covered by deposits from glaciers, mudflows, and the Young Cone. The Old Cone makes up about 80% of the volcano's size today. Rocks from the Old Cone are about 160,000 years old. After the Old Cone stopped erupting, erosion shaped the volcano until the big sector collapse happened.
The Young Cone started growing after the collapse, filling the giant scar left behind. This activity involved different types of lava and lava domes. Each time lava came out, it was often preceded by explosive eruptions that created hot ash flows. Some rocks from the Young Cone are about 100,000 years old. La Poruña, the smaller cone nearby, is also very old, between 110,000 and 56,000 years old.
A large eruption covered parts of the volcano with ash about 15,000 years ago. The big Plinian eruption happened even more recently, about 10,000 years ago. After this, four small lava domes formed near the summit.
Recent Activity of San Pedro
Eruptions at San Pedro have been reported in history, possibly starting in 1885. A newspaper mentioned "strong shaking of the earth" and lots of steam. Other reported eruptions were in 1901, 1910, 1911, 1938, and a small one in 1960. Some other dates are also mentioned, like 1870, 1916, 1917, and 1923. However, these historical eruptions are not always certain. They were likely "phreatic," meaning they were caused by steam explosions, not new magma. No geological evidence has been found for them. This volcanic activity makes San Pedro one of the highest active volcanoes.
Today, the only ongoing activity at San Pedro is fumaroles in the eastern summit crater. These vents release steam, which forms sulfur deposits. Scientists measure the amount of sulfur dioxide gas coming out. In 2013, it was about 161 tons per day. There have also been reports of sulfur smells at La Poruña and some seismic activity (earthquakes) at the volcano.
Scientists watch San Pedro because future eruptions could be dangerous. One risk is large debris avalanches or pyroclastic flows. These could reach nearby roads. Another risk is a big explosive eruption, which could send ash high into the sky and cover the whole region. Because the volcano is so tall, parts of it could also collapse. Several seismic stations monitor earthquakes at San Pedro. The Chilean government agency, SERNAGEOMIN, also publishes a volcano hazard level for it.
Climbing San Pedro Volcano
San Pedro is a popular mountain to climb. This is partly because it's close to the tourist town of San Pedro de Atacama. The easiest way to climb it is by going up the north slopes to a saddle, then following the east slope to the very top.
The first people to climb San Pedro were George Courty from France and Filemón Morales from Chile. They reached the summit on July 16, 1903.
Images for kids
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San Pablo volcano as seen from just below the summit of San Pedro
See also
In Spanish: Volcán San Pedro (Antofagasta) para niños
- List of volcanoes in Chile
- List of Ultras of South America
