Mount Everest, also known as Chomolungma, has grown about 15 to 50 meters (50 to 164 feet) higher over the past 89,000 years than expected, according to a modeling study released Monday. The culprit is a nearby river eroding and pushing down land, causing the ground under Mount Everest to rebound and lift.

And, perhaps just as interesting, the answer for Everest’s growth is down at ground level — specifically the Arun River north of the mountain. Thousands of years ago, its course of flow was changed due to erosion, and the Arun connected with its lower reach and became part of the nearby Kosi River system.

Mount Everest is Earth's tallest mountain - towering 5.5 miles (8.85 km) above sea level - and is actually still growing. While it and the rest of the Himalayas are continuing an inexorable uplift that dates back to their birth roughly 50 million years ago when the Indian subcontinent collided with Eurasia,