Why in the News?

The Arun River, which flows across Nepal and Tibet, is eroding rock and soil in its basin, leading to the rise of Mount Everest by up to 2 mm a year.

How is Arun River making the Everest taller?

The Arun River is contributing to the rise of Mount Everest through a process called isostatic rebound. Here’s how it works:

1. River Incision:

The Arun River, which flows about 75 km from Mount Everest, is eroding large amounts of rock and soil from the surrounding landscape.
This process of erosion reduces the weight on the Earth’s crust in the Arun River basin.
A study by UCL suggests that the Arun River’s ability to carve out large amounts of rock and other materials may be due to it capturing another river or water system in Tibet.
This process is known as River Incision, where the river cuts downward into its bed, deepening its channel.
The erosion began to accelerate around 89,000 years ago when the Arun River merged with the Kosi River, removing large amounts of landmass and further reducing the weight on the region’s crust.

2. Isostatic Rebound:

When the weight of the land (due to rocks, soil, or even ice) decreases, the Earth’s crust rises to balance the change.
This is similar to how a boat rises in water when heavy cargo is removed.
The removal of landmass in the Arun River basin allows the crust underneath Mount Everest to rise.

The Arun River originates in the Tibet Autonomous Region of China, where it is known as Phung Chu or Bum-chu in Tibetan.
It flows into Nepal and confluences with the Sun Koshi and Tamur River at Tribenighat, forming the Sapta Koshi River.
Tributaries:
- Left tributaries: Yeru Tsanpo, Trakar-chu.
- Right tributary: Barun River.
At the Nepal border, the Arun River is approximately 3,500 meters (11,500 ft) above sea level.
The river drains into the Koshi River, significantly contributing to the Sapta Koshi River system in Nepal.
It is the largest trans-Himalayan river in Nepal, playing a crucial role in supporting the region’s hydrology and ecosystems.
It provides around 37% of the total water in the Sapta Koshi system, following the Sun Koshi which contributes 44%.
Recently, the Arun-III Hydro Power Project (900 MW), which constructed with $6.95b Indian assistance, achieved a milestone with a tunnel breakthrough.

[2017] With reference to river Teesta, consider the following statements:

1. The source of river Teesta is the same as that of Brahmaputra but it flows through Sikkim.

2. River Rangeet originates in Sikkim and it is a tributary of river Teesta.

3. River Teesta falls into Bay of Bengal at the border of India and Bangladesh.

Which of the statements given above is/are correct?

(a) 1 and 3 only

(b) 2 only

(d) 1, 2 and 3