The Amazon, the world’s largest river, is a bewildering array of river channels and connected floodplains supporting the most diverse ecosystem on Earth. This region also exerts a dominant control on the world’s climate. Until about 11 million years ago, the river flowed westward to the Pacific Ocean, but due to the rise of the Andean mountain chain now flows east to the Atlantic.
Next week, we’ll be in the heart of the Brazilian Amazon, near the frontier town of Tefé, to conduct research on the river, which there is named the Solimões River. We’re going as part of an international project to study the form of the modern-day Amazon River and to learn how it can help us interpret the deposits of such huge rivers within the ancient geological record.
The Amazon floodplain boasts a richness of flora and fauna.
The three of us will work in a field team with professors Renato Paes de Almeida and Bernardo Freitas and two of their graduate students from the universities of São Paulo and Campinas. We’ll be traveling in – and living on – a riverboat during our time there.
This river is huge – the main channel can be up to 4 kilometers wide and 60 meters deep, and the water level can change by up to 15 meters between low- and high-flow seasons. We surveyed part of the Solimões River in July when the river was high, sailing over sandy river islands and using state-of-the-art geophysical survey techniques to measure the shape of the riverbed, the patterns of flow in the water and the makeup of the sediments in the subsurface.
This colored topographic map of our study area in the Amazon River shows the complexity of the modern-day river and older river channel networks. The map was constructed from Shuttle Radar Topography Mission data, and the elevation difference between the areas in red (low) and green (high) is roughly 60 meters.
Now we’re headed back in the dry season, when part of the riverbed becomes exposed, to study what the deposits of these river islands look like – both in recent sediments and those laid down thousands of years ago. In this low-water survey, we’re using more traditional techniques – field examination of exposed sediments, photomontages, field sketches and sampling – to help reveal the secrets of these river sediments.
Storm clouds loom over the river. Our last trip took place during the rainy season, but now it is the dry season. The low water will allow us to survey the exposed river bed.
Our aim is to establish a model for how these sediments evolved through time. The model can help us interpret deposits of other giant rivers locked up in the geological past – such as the rivers of Illinois some 300 million years ago.
Stay tuned for our blogs from the field!
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