The Amazon: from wetland to river

Nov 22, 2010
Satellite image of the mouth of the Amazon River.

( -- How do you turn a mega wetland into the world's largest river? By continental tilting, suggests an international team led by a University of Sydney group.

PhD candidate Grace Shephard, Professor Dietmar Müller and a team of international colleagues have reported their discovery in the journal Nature Geoscience.

The world's largest river, the , used to be a large wetland connected to the Caribbean until 14 million years ago, when the Amazon River as we know it today formed, flowing into the Atlantic Ocean.

The uplift of the Andes mountains was assumed to be the main culprit causing this enormous change in continental drainage, blocking westward flow.

In contrast, Shephard and her colleagues suggest that progressive continental tilting established a gently inclined drainage surface that forced water from a giant catchment to flow to the east, starting at about 14 million years ago.

"We had a hunch that the ultimate forces leading to this fundamental shift in continental topography had something to do with the westward motion of South America over dense, sinking mantle rocks while the Atlantic Ocean opened up," she said.

"We used a high-performance computer model to simulate the workings of this giant tectonic conveyor belt, with South America progressively being translated westward over an ancient subduction zone along the continent's west coast."

Professor Müller said here, along the edge of the Pacific, ocean crust had plunged into the sticky rocks of the Earth's mantle for eons.

"This process created a massive crustal graveyard deep inside the Earth, where huge masses of old, cold tectonic slabs are sinking, drawing the surface down," he said.

"As South America made its way westward over this 'slab burial ground', the continent's northeast was progressively drawn down by several hundred meters, creating something akin to the world's largest water slide."

Their work is significant in that it shows that the interplay between shifting continents and the slow convection of mantle rocks underneath, akin to croutons floating on a thick pumpkin soup, can fundamentally change the Earth's surface topography, river systems, and ultimately ecosystems through geological time.

Could this happen in Australia? It's happened many times in the past. Eastern Australia is known to have swung up and down like a giant wobble board in response to moving over slab graveyards in the Earth's deep mantle, creating and later destroying large river systems like the one that's arguably formed Sydney's foundation: the Hawkesbury sandstone.

Explore further: Why it is so hard to predict where and when earthquakes will strike

More information: Paper online:

Related Stories

The continents as a heat blanket

Jan 22, 2009

Drifting of the large tectonic plates and the superimposed continents is not only powered by the heat-driven convection processes in the Earth's mantle, but rather retroacts on this internal driving processes. In doing so, ...

Recommended for you

Growing interest in geotourism

2 hours ago

According to the Geological Survey of Sweden, (SGU), there is growing interest among the country's municipalities, organisations and other local initiatives in running geotourism and geoparks. Among those ...

Australia on path to join supercontinent 'Amasia'

2 hours ago

The possibility that Earth could have a supercontinent that would occupy two-thirds of the planet's surface in a couple of hundred million years' time is just one of the geological projects being investigated ...

Why the Nepalese quake was so destructive

2 hours ago

The earthquake, which wreaked havoc in the Kathmandu Valley of Nepal on Saturday about noon local time, was the strongest quake in the world so far this year. With a magnitude of 7.8 it was felt over a very ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.