Central Indian Ridge

A big ridge sits under the sea.

It is in the Indian Ocean. This ridge is very long. It goes from north to south.

This ridge helps move parts of the earth. It sits between two large plates. These plates move away from each other.

Hot melted rock comes up from the ridge. This makes small mountains. These mountains rise above the floor.

One small island sits near the ridge. It is called Rodrigues Island. It is the only part above the water.

It is a very deep place under the waves.

The Central Indian Ridge is a big ridge under the sea. It runs from north to south in the western Indian Ocean. This ridge sits between the African plate and the Indo-Australian plate. These plates are large parts of the Earth's surface. The ridge is a place where the plates move apart.

Near the Equator, the ridge moves at 30 mm per year. Near its southern end, it moves at 49 mm per year. In some spots, the ridge has a deep valley. This valley is 500 to 1000 meters deep. Hot melted rock comes up from volcanic ridges. These ridges rise 100 to 200 meters above the valley floor.

One small island sits near the ridge. It is called Rodrigues Island. It is the only part of the ridge above the water. This island is part of a spot called the Rodrigues triple junction. This is where three different plates meet.

The ridge is very deep. At 20°S, it is 3200 meters deep. Near the southern end, it reaches 4000 meters deep.

The Central Indian Ridge is a huge mountain range under the sea. It runs north to south in the western Indian Ocean. This ridge is a place where Earth's giant plates pull apart. It helps separate the African plate from the Indo-Australian plate. This ridge is very important for understanding how our ocean floor grows. It is a special part of the deep, dark ocean world.

This ridge works by spreading the ocean floor apart. Near the Equator, the spreading rate is 30 mm per year. Near the southern end, it moves faster at 49 mm per year. This movement creates a deep axial valley. That valley is 500 to 1000 meters deep. Melted rock rises up from small volcanic ridges. These ridges are 1 to 2 km wide. They rise 100 to 200 meters above the valley floor.

Scientists have studied how this ridge formed over millions of years. About 38 million years ago, the ridge opened up. This happened as the Mascarene Plateau and Chagos-Laccadive Ridge moved apart. A special heat source called the Réunion hotspot helped this happen. This is the only hotspot known to touch the ridge. The hotspot crossed the ridge near 18 to 20°S. It moved from the Indian plate to the African plate.

There are many specific details about the ridge's shape. The axial depth changes as you move south. It is 3200 m deep at 20°S. It reaches 4000 m deep near the Rodrigues triple junction. One huge feature is the Mary Celeste Fracture Zone. This zone is almost 300 km long at 18°S. Most ridge segments are 50 to 100 km long. They are separated by faults that are 30 km long.

You can think of the ridge like a slow zipper. As the zipper opens, new ocean floor is made. The only part of this ridge above water is Rodrigues Island. This island sits near the Rodrigues triple junction. This is a spot where three different plates meet. The island is near Mauritius and the ridge. It shows us how heat from deep inside Earth can build islands.

The Central Indian Ridge is a massive underwater mountain range. It runs north to south through the western Indian Ocean. This ridge is a mid-ocean ridge, which is a place where tectonic plates pull apart. This process creates new ocean floor. The ridge serves as a major boundary between different parts of the Earth's crust. It traditionally separates the African plate from the Indo-Australian plate.

This ridge is categorized as having a slow to intermediate spreading rate. Spreading occurs as the plates move away from each other. Near the Equator, the plates move apart at 30 mm per year. At the southern end, near the Rodrigues triple junction, the rate increases to 49 mm per year. This movement creates a distinct shape in the ocean floor. A deep axial valley forms in the center of the ridge. This valley is between 500 and 1000 meters deep.

Small volcanic ridges provide the melt supply for the ridge. These axial volcanic ridges are 15 km long and 1 to 2 km wide. They rise 100 to 200 meters above the floor of the axial valley. The ridge is not one continuous line. Instead, it is made of segments that are 50 to 100 km long. These segments are separated by transform faults that are 30 km long. There are also non-transform discontinuities that are 10 km long. One massive exception is the Mary Celeste Fracture Zone. This feature is almost 300 km long and is located at 18°S.

The shape of the ridge changes depending on its location. Between 21°S and the Mary Celeste Fracture Zone, the ridge deviates westward. In this section, the larger offsets switch from right-lateral to left-lateral. North of 18°S, the offsets return to being right-lateral. The southern section between 13°S and 25°S is near-orthogonal to the spreading direction. This means the spreading happens at a nearly right angle to the ridge. North of the Argo Fracture Zone, the ridge is highly oblique. This means it is tilted at an angle. In the far north, the ridge includes the Carlsberg Ridge. This northern section trends north-northwest and lacks fracture zones.

Geologists study the boundaries of these plates to understand Earth's movement. While the ridge separates the African and Indo-Australian plates, other boundaries are more complex. The Owen Fracture Zone is at the northern end of the ridge. It was traditionally thought to separate the Indian-Australian plate from the Arabian plate. However, movements in this zone are negligible. Arabia and India actually move together as a single plate. This single plate is separated from the Australian plate by the India–Capricorn boundary. This is a diffuse boundary, meaning it is spread out over a wide area. It stretches from Chagos Bank to the Ninety East Ridge. This boundary likely began in the Late Miocene. It may be related to the opening of the Gulf of Aden and the uplift of the Himalayas.

The history of the ridge involves interactions with a hotspot. A hotspot is a source of intense heat from deep within the Earth. The Réunion hotspot is the only one known to have interacted with the Central Indian Ridge. The ridge opened about 38 million years ago. This happened during the separation of the Mascarene Plateau and the Chagos-Laccadive Ridge. The hotspot crossed the ridge near 18-20°S. It moved from the Indian plate to the African plate about 47 million years ago. The Réunion hotspot track includes the Chagos-Laccadive Ridge. It also produced the Deccan Traps in northwest India at 66 million years ago.

There is only one structure near the ridge that sits above the water. This is Rodrigues Island. It is located at the Rodrigues triple junction. A triple junction is a point where three different tectonic plates meet. This junction is located between Mauritius and the Central Indian Ridge. The Rodrigues Ridge reaches the main ridge at 19°S. It does this through a series of ridges called the Three Magi. Scientists believe the Réunion hotspot created this area. They found that volcanic rocks from Rodrigues Island are similar to rocks from Réunion and Mauritius. These rocks are between 1.30 and 1.58 million years old.