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Imaggeo on Mondays: Science above the Amazon rainforest

Imaggeo on Mondays: Science above the Amazon rainforest

The color and symmetry of the Amazon Tall Tower Observatory (ATTO) sticks out against the endless green of the rainforest. Built in a remote and pristine location, the ATTO tower is the tallest construction in South America. In a joint Brazilian-German project, atmospheric scientists aim to unravel the interaction of pristine rainforest with the atmosphere. With its height of 325 meters, the ATTO tower allows for studying atmospheric processes at different spatial scales.

Description by Achim Edtbauer, as it first appeared on imaggeo.egu.eu.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

GeoSciences Column: Forests in flux – log-jams in the Amazon

GeoSciences Column: Forests in flux – log-jams in the Amazon

Collapsing dams are a staple of disaster films, but the form that these take in natural systems is also surprisingly varied. Streams and rivers can be blocked by a range of rapid and gradual inputs. One of the lesser-known causes of stream blockage is through the accumulation of large woody debris – tree trunks and large branches – to form a log jam.

The impact of these jams on river geomorphology can be varied, but in some extreme cases, when they break, large flood waves can wash out huge downstream areas. This kind of hazard is often poorly understood, so a new study exploring how logjams in Bolivia can drive downstream flooding published in Earth System Dynamics by Umberto Lombardo provides an important addition to our understanding.

To form a log-jam, tree trunks and other large woody debris needs to end up in the river through erosion and transport processes. The majority of the rivers in the assessed area meander back and forth, which encourages erosion of the river banks; this can topple trees into the river. This bank erosion provides the source of the woody debris which then gets stuck in the channel, beginning the construction of a log-jam.

Once the jam is formed there is potential for flooding, which has important consequences for the surrounding forest. Behind the dam, silt and sand accumulates, and once the river either breaks the dam or redirects around it, sediment is also distributed downstream, along with the woody debris.

Using satellite imagery, Lombardo explores a chunk of the Bolivian part of the Amazon rainforest to look for the effects of log-jam induced flooding on forest dynamics. He shows in this study that the sudden influx of mud and silt onto the forest floor characteristically results in the die-off of much of the vegetation. Where floods occur repeatedly, the dense rainforest ecosystem is replaced by a drier, more savannah-like ecosystem.

Evolution of the Cuberene River. The river flows from southwest to northeast. From 1995 to 2016, the location of the log-jams propagated upriver, along the two rivers that form the Cuberene. By 2016, large areas that were forested in 1995 had been transformed into savannah. An east–west road crossing the Cuberene in 1995 is completely obliterated in the 2016 image. Also notice how the light green areas in early stages of the successional process in 1995 are already forested by 2016. From Lombardo U., 2017.

The flood-induced ecosystem change is not an isolated one, either; in the study area, the amount of forest killed by floods is nearly as great as the amount lost to deforestation for agricultural growth, and the near-annual recurrence of these events in many rivers means that it is a consistent cause of ecological shifts.

From a human perspective, these log-jams are a risk that may not be appreciated. Recent studies have shown that human driven deforestation can accelerate the rate at which river banks in tropical regions erode; so while the removal of trees may initially reduce the propensity for log-jams in extensively managed stretches of river, the faster rate of meandering may also lead to log-jam formation further down the line sooner than we might think. A clearer understanding of such river systems, where log-jam formation and coupled flooding is part of the normal evolution of the stream system, would serve us well in rapidly developing tropical countries that rely on forest ecosystems.

While the dynamics of log-jams have been studied in more temperate regions, this study represents a significant step into the unknown in tropical regions. The Amazon as a whole is a crucial component of the global carbon cycle, so a clearer understanding of the feedbacks between rivers, erosion, and the forest ecosystem will allow us to create more nuanced models of the rainforest dynamics.

The more scientists study forests, the clearer it becomes that these ecosystems regularly undergo significant disturbances simply as part of their natural cycles. Forest fires and pest outbreaks can disrupt a given stand of forest; log-jams are another example of a disturbance, this time closely associated with river dynamics. Forests renew and regenerate themselves at a range of scales, from individual trees to whole swathes of woodland, and log-jams provide an additional mechanism that can lead to die-off of mature forest and replacement by new growth.

By Robert Emberson, a science writer based in Canada

References

Lombardo, U.: River logjams cause frequent large-scale forest die-off events in southwestern Amazonia, Earth Syst. Dynam., 8, 565-575, https://doi.org/10.5194/esd-8-565-2017, 2017

Imaggeo on Mondays: One of the oldest evergreen rainforests in the world

Imaggeo on Mondays: One of the oldest evergreen rainforests in the world

A blazing sky and shimmers cast by water ripples frame the spectacular beauty of one of the world’s oldest treasures: an evergreen rainforest in Thailand. Today’s featured image was captured by Frederik Tack, of the Institute for Space Aeronomy in Brussels.

This picture was taken during sunset between the limestone mountains with the sunlight reflecting on beautiful Ratchaprapha lake in Khao Sok National Park.

Khao Sok National Park is one of the oldest evergreen rainforests in the world since Thailand has remained in a similar equatorial position throughout the last 160 million years. The climate in the area has been relatively unaffected by ice ages, as the landmass is relatively small and has seas on both sides. Even whilst other places on the planet were suffering droughts, the Khao Sok region still received enough rainfall to sustain the forest.

Khao Sok is also famous for its vertiginous limestone cliffs or ‘karst’ mountains. In most of the region, ground level is about 200m above sea level with the average mountain heights around 400m. The tallest peak in the National Park is 960m high. The national park area is inhabited by a large range of mammals such as tigers, elephants, tapirs and many monkey species. Birds such as hornbills, banded pittas and great argus are as well forest residents. Less commonly seen reptiles include the king cobra, reticulated python, and flying lizards.

One of the most interesting areas is stunningly beautiful Cheow Lan or Ratchaprapha Lake in the heart of the National Park. It is an 165-square-kilometre artificial lake, created in 1982, by the construction of Ratchaprapha Dam as a source of electricity.

By Frederik Tack, of the Institute for Space Aeronomy in Brussels

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: Through the hole

Imaggeo on Mondays: Through the hole

The Gunung Mulu National Park is an area so geologically remarkable and home to such incredibly diverse fauna and flora it has been declared a World Heritage Area.  Located on the island of Borneo, the park is famous for its over 100 different palm species and 3500 other plant types. Geologically speaking, a trip though the varied landscapes will be rewarded with views of deep gorges and hidden valleys, as well as towering limestone and sandstone pinnacles. The predominantly calcareous landscape means most make the journey to remote area to catch a glimpse of the world’s second largest cave chamber. With dimensions of 600 m by 415 m and 80 m high, Sarawak Chamber is a natural wonder worthy of making the journey to Borneo for!

“The picture was taken in February 2014 while I was on a two month trip to Indonesia and Malaysia after graduating from my Master studies. Eventually I found one of the most beautiful places on the island of Borneo: the Gunung Mulu National Park,” explains Juliane Krenz, a PhD candidate at the Department of Environmental Science of the University of Basel.

Aside from the staggering Sarawak Chamber, the national park is crisscrossed by at least 295 km of explored caves.  Made up of the Mulu Sandstone Formation, overlain by the Melinau Formation – which formed in coral rich lagoons some 20 million years ago – the caves are home to a host of species, from bats to swiftlets.

“After spending a few days exploring one of the largest cave systems in the world, I wanted to get deeper into the rainforest and climb Mount Api to see the so-called “pinnacles” – an incredible limestone karst formation everybody was talking about,” Juliane says.

The journey to reach the “pinnacles” involved an hour’s boat ride and three hours walk through the rainforest, eventually reaching a small base camp impressive for its setting: three houses next to a crystal clear stream surrounded by mountains covered in dense forest.

The hike to the sandstone spires began in earnest the next morning. To reach the impressive formations Juliane had to climb an endless number of natural steps made of slippery roots and stones of varying heights from a comfortable 20cm up to 1m, with a total elevation increase of 1200 m in little over 2km – turning the hike into an adventurous climbing trip.

“After 3 hours hiking mostly vertically we reached the top and looked down on an innumerable amount of silver-greyish rock pinnacles spiking out between the dense bright green forest, some of them being up to 40m tall. None of us would have guessed that there were so many,” describes Juliane.

Capturing the beauty of the setting was no easy task.

“I had seen many impressive photographs of the spikes but I was looking for the special focus. Eventually I chose the hole as a frame making the largest pinnacles look like they are part of a miniature world – like me wandering through the rain forest.”

By Laura Roberts Artal , EGU Communications Officer and Juliane Krenz, a PhD candidate at the Department of Environmental Science of the University of Basel.

For more information on the Gunung National Park:

In 1977-78 there was a large expedition (followed by many others known as the Mulu Cave project) founded by the Royal Geograpical Society to explore the dimensions of the cave system. The “pinnacles” at Mount Api are part of the limestone ridge between North Thailand and New Guinea.  The area is full of limestone spikes of various sizes (from few centimeters up to several meters) that are formed through weathering and dissolution over centuries. Nowadays, most research is focused on the ecology and biodiversity in the caves and the surrounding areas.

An earlier version of this post stated Sarawak Chamber was the largest cave chamber in the world. That accolade goes to Hang Sơn Đoòng in Vietnam. With thanks to @TerjeSolbakk for helping us improve this post. 

 

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.