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Geosciences Column: How erupting African volcanoes impact the Amazon’s atmosphere

Geosciences Column: How erupting African volcanoes impact the Amazon’s atmosphere

When volcanoes erupt, they can release into the atmosphere a number of different gases initially stored in their magma, such as carbon dioxide, hydrogen sulfide, and sulfur dioxide. These kinds of gases can have a big influence on Earth’s atmosphere, even at distances hundreds to thousands of kilometres away.

A team of researchers have found evidence that sulfur emissions from volcanic eruptions in Africa can be observed as far as South America, even creating an impact on the Amazon rainforest’s atmosphere. The results of their study were published last year in the EGU journal Atmospheric Chemistry and Physics.

Amazon Tall Tower Observatory based in the Amazon rainforest of Brazil (Credit: Jsaturno via Wikimedia Commons)

In September 2014, the Amazon rainforest’s atmosphere experienced an unusually sharp spike in the concentration of sulfate aerosols. During this period, the Amazon Tall Tower Observatory (ATTO) based in Brazil reported levels of sulfate never recorded before in the Amazon Basin.

Sulfate aerosols are particles that take form naturally from sulfur dioxide compounds in the atmosphere. When sulfate aerosols spread throughout the atmosphere, the particles often get in the way of the sun’s rays, reflecting the sunlight’s energy back to space. These aerosols can also help clouds take shape. Through these processes, the particles can create a cooling effect on Earth’s climate. Sulfate aerosols can also facilitate chemical reactions that degrade Earth’s ozone layer.

Fossil fuel and biomass burning have been known cause an increase in atmospheric sulfate, but researchers involved in the study found that neither human activity increased the level of sulfate in the atmosphere significantly. Instead, they examined whether a volcanic eruption could be responsible.

Scientists have suggested for some time that sulfur emissions in the Amazon could come from African volcanoes, but until now they’ve lacked proof to properly justify this idea.

Edited Landsat 8 image of the volcanoes Nyamuragira and Nyiragongo in Congo near the city of Goma. (Credit: Stuart Rankin via flickr, NASA Earth Observatory images by Jesse Allen, using Landsat data from the U.S. Geological Survey.

However, in this study the research team involved caught volcanic pair in the act. By analysing satellite images and aerosol measurements, the researchers found evidence that in 2014, emissions from the neighboring Nyiragongo-Nyamuragira volcano complex in the Democratic Republic of the Congo, central Africa, increased the level of sulfate particles in the Amazon rainforest’s atmosphere.

Satellite observations revealed that volcanoes experienced two explosive events in September 2014, releasing sulfur emissions into the atmosphere. During that year, the volcanic complex was reportedly subject to frequent eruptive events, sending on average 14,400 tonnes of sulfur dioxide into the atmosphere a day during such occasions. This amount of gas would weigh more than London’s supertall Shard skyscraper.

Map of SO2 plumes with VCD > 2.5 × 1014 molecules cm−2 color-coded by date of observation. The 15-day forward trajectories started at 4 km (above mean sea level, a.m.s.l.) at four locations within the plume detected on 13 September 2014 (light blue) are indicated by black lines with markers at 24 h intervals. (Credit: Jorge Saturno et al.)

The images further show that these emissions were transported across the South Atlantic Ocean to South America. The sulfate particles created from the emissions were then eventually picked up by an airborne atmospheric survey campaign and the ATTO in the Amazon.

The researchers of the study suggest that these observations indicate that African volcanoes can have an effect on the Amazon Basin’s atmosphere, though more research is needed to understand the full extent of this impact.

By Olivia Trani, EGU Communications Officer

References and further reading

Volcanic gases can be harmful to health, vegetation and infrastructure. Volcano Hazards Program. USGS.

Aerosols and Incoming Sunlight (Direct Effects). NASA Earth Observatory

Saturno, J., Ditas, F., Penning de Vries, M., Holanda, B. A., Pöhlker, M. L., Carbone, S., Walter, D., Bobrowski, N., Brito, J., Chi, X., Gutmann, A., Hrabe de Angelis, I., Machado, L. A. T., Moran-Zuloaga, D., Rüdiger, J., Schneider, J., Schulz, C., Wang, Q., Wendisch, M., Artaxo, P., Wagner, T., Pöschl, U., Andreae, M. O. and Pöhlker, C.: African volcanic emissions influencing atmospheric aerosols over the Amazon rain forest, Atmospheric Chemistry and Physics, 18(14), 10391–10405, doi:10.5194/acp-18-10391-2018, 2018.

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