Andean orogeny

Big mountains are growing.

They are called the Andes. They are in South America.

Deep under the sea, the land moves. One piece of land slides under another. This pushes the land up high.

This makes the mountains very tall. The mountains also change the weather. They can block wet air from moving.

This makes some places very dry. One dry place is the Atacama desert.

The mountains are still growing today. It is a very slow change.

The Andes are huge mountains in South America. They are still growing today. This happens because of a process called orogeny. Orogeny is the way mountains are made.

Deep under the ocean, plates of land move. One plate slides under the South American plate. This is called subduction. This movement pushes the land up high.

Around 90 million years ago, things changed. The plates moved in a new way. This helped the mountains rise even more. In some places, the plates slid in a flat way. This is called flat-slab subduction. This can stop volcanoes from forming.

The mountains also change the weather. They act like a big wall. They stop wet air from reaching some areas. This helped make the Atacama desert very dry.

In parts of Bolivia, the land rose very high. We call this high land the Altiplano. It is a big, flat area between mountains.

It rose many meters over time. The Andes keep changing as the plates move.

The Andes are a massive chain of mountains in South America. They are still growing today through a process called orogeny. This is the way mountains are built over long periods of time.

This mountain building is driven by subduction. This happens when one piece of the Earth's crust slides under another. In this case, oceanic crust is sliding under the South American continent. This movement pushes the land upward to create high peaks. It is a slow but very powerful force.

The way these mountains form has changed many times. Long ago, the process involved pulling the land apart. This created basins and large groups of rocks called batholiths. Around 90 million years ago, the style of subduction changed. The oceanic crust became warmer and younger as it slid under the continent. This caused the land to squeeze and push upward. This change also helped cause erosion. It may have been linked to the opening of the South Atlantic Ocean.

Scientists have studied these changes for a long time. We know that different parts of the Andes have different histories. For example, the Farallon Plate once existed under the ocean. It later broke into the modern Cocos and Nazca plates. This breakup caused many changes in how the mountains grew. In the Oligocene period, about 30 million years ago, the mountains began to rise significantly. Many different phases of mountain building have happened since then. These include the Incaic and Quechua phases in places like Peru.

There are many specific details about how different areas changed. In northern Peru, the mountains moved in stages called phases. The Incaic Phase was a very large event for that region. In Bolivia, a high flat area called the Altiplano rose up. It rose from low ground to more than 3,000 meters above sea level.

Some parts of the Altiplano rose by 2,000 to 3,000 meters in just ten million years. In Colombia, different pieces of land collided to form new parts of the continent.

The mountains also change how the world works around them. The Andes act like a giant wall for the weather. They stop wet air from moving into the Atacama desert. This makes the desert a very dry place. This dryness changes how rivers move soil and rocks.

The rise of the mountains also helped create the modern Amazon River. Before the mountains rose, water in northern South America flowed toward the Pacific Ocean. Now, the high land changes the path of the water. The mountains and the weather work together to shape the land.

The Andean orogeny is an ongoing geological process that builds the Andes mountains. This mountain-building event is driven by a subduction system along the western edge of South America. Subduction occurs when one tectonic plate slides beneath another. In this region, oceanic lithosphere is being pushed under the continental crust. This process has been active since the breakup of the supercontinent Rodinia. The mountains we see today are the result of millions of years of complex tectonic shifts.

The mechanics of the Andes have changed significantly over time. During the Jurassic and Early Cretaceous, the region experienced extensional tectonics. This means the crust was being pulled apart, creating rifts and back-arc basins. Large groups of igneous rocks called batholiths were also formed during this time. This was likely caused by the subduction of cold oceanic lithosphere. However, around 90 million years ago, the character of the orogeny shifted. Warmer and younger oceanic lithosphere began to subduct under South America. This change caused intense contractional deformation and significant uplift.

Different parts of the Andes have unique geological histories. In Colombia, tectonic blocks of continental crust separated during the Jurassic. These blocks re-joined the continent through oblique collision in the Late Cretaceous. This process of adding new land is called accretion. Around 65 million years ago, the Caribbean large igneous province collided with South America. This event helped form the magmatic arcs seen in Ecuador and Colombia today. In Peru, the orogeny occurred in specific stages known as phases. The Mochica Phase involved the folding of sediments near the coast. Later, the Incaic Phase caused massive horizontal shortening in the mountains.

The mountains also undergo a process called flat-slab subduction. This happens when the subducting plate moves at a very low angle. This process can suppress arc volcanism and cause crustal shortening. Currently, flat-slab subduction is found in parts of Colombia, Ecuador, Peru, and Chile. This specific type of movement affects how the crust deforms. It can also lead to the removal of the lower part of the upper plate. This removal can cause localized extensional tectonics due to gravitational collapse.

In the Oligocene epoch, about 30 million years ago, a major change occurred. The Farallon Plate broke apart into the modern Cocos and Nazca plates. The new Nazca Plate began subducting into South America in an orthogonal direction. This means it moved more directly toward the continent. This shift caused significant uplift, especially during the Miocene epoch. Since the Oligocene, the Andes have risen significantly across the entire range. This period marked a major turning point for the height of the mountains.

One of the most striking features is the Altiplano in Bolivia. This is a massive, high-altitude plateau located between Lake Titicaca and the Cordillera Real. The Altiplano rose from low elevations to over 3,000 meters above sea level. In some areas, the land rose by 2,000 to 3,000 meters in only ten million years. This uplift was likely caused by horizontal shortening of the crust. It may also have been influenced by increased temperatures in the mantle.

The Andes also have a massive impact on the Earth's climate and water systems. The high mountains act as a topographic barrier for air masses. They block humid air from reaching the Atacama desert, creating extreme aridity. This dryness changes how erosion and rivers move mass across the land. The rise of the mountains also changed the path of water in South America. Before the mountains grew, many rivers flowed toward the Pacific Ocean. The uplift helped create the modern Amazon River by changing the drainage patterns.