Rapid Processes in Source-to-Sink Systems - Part I

In our blog post series, we previously mentioned how geological processes act in different time scales. These mechanisms are either long-lasting (e.g. tectonically driven orogenic uplift) or abrupt (climatic events). Within our previous blog post, we focused on the former -  those processes considered to be ‘slow’ in the geological time scale, going back from several decades to millions of years in our Earth’s history. In this post we will dive into much faster processes that shape the surface of our planet. These processes can take place within hours, days, or even years up to several thousands of years (Romans et al. 2016).

1. Surface processes vary with environmental changes 

The Earth’s surface is a natural archive that stores information on past environmental conditions. This information can be found in the landscape shape, in rocks, sediments, and minerals. Changes and perturbations in the environment, for example, floods and landslides, resulting in changes in the landscape. These changes can be understood as a break in the steady-state, bringing the landscape to a transient state. You can read more about steady and transient states in our last blog post. Floods and landslides are typical examples of fast processes that might reshape the landscape. They can easily destroy buildings, block roads and railways, and even claim people’s lives. A result of the aforementioned rapid climatic events (floods and landslides), mostly caused by an abrupt increase in precipitation, is the formation or alteration of river systems. These fluvial regimes show distinct morphologies (Fig.01), such as meanders or braided rivers.

Fig.01: River morphologies. (a) Meander showing typical huge flow loops (nwrm.eu). (b) Braided river regimes (uoregon.edu).

Another example of a fast process that can alter the landscape is glaciation, which is caused by extremely cold periods. These periods, in turn, can produce optimal conditions for glacier formation. Once glaciers form and advance through valleys, they can easily transform the landscape by carving the surface underneath them. Examples of the product of glacier advancement and retreat are valleys that resemble the letter U (Fig.02). These valleys can be found in mountainous regions around the world, for instance, in the Alps, Caucasus, Andes, Himalayas, and others. However, the extreme cold periods are cyclic, and eventually, they give in to warmer conditions, resulting in the thawing of glaciers, revealing the U-shaped valley (see GIF.01 and Fig.02).

GIF.01 By Cecilia Bernal [CC BY-SA 4.0], via Wikimedia Commons.

Fig.02: U-shaped valley as demonstrated by the orange lines. Grönbach valley, near Brienzer Rothorn, Emmental Alps, Switzerland. Photo by Ewerton da Silva Guimarães.

Besides the obvious reshaping of the landscape, the environmental changes due to fast climatic processes can be indicated by surface sediments, e.g. by their grain roundness or size. These grain characteristics can be retrospectively used as an indicator for past underlying transport mechanisms of the affected sediments.

2. Examples of observed changes in the landscape

Rapid climatic changes shape the Earth even on human-perceptible timescales. Here we present some widely known events, especially due to the impact that they had on human populations: 

Floodings in Germany and Belgium: Climatic induced landscape changes

In July 2021, we learned that our path to predicting climate-related disasters is far from over. Within 24 hours of heavy rains on the 13th of July 2021, streams were fed to such a level that houses and cars were washed along (Fig.03). This was accompanied by the trigger or enormous landslides. As a consequence, nearly 200 people died by the 20th of July of the same year, with the most affected areas concentrated in central and southern Germany. Even though the time scale of these processes was immediate in geological timescales, the impact on human life had tremendous consequences. The sedimentological record will also record the massive outburst of water. 

For more information, check an expanded version of this news.

Fig.03: Aerial images of the flooding events in Germany. On the left, the population before the onset of the floods. On the right, the devastating consequences, carrying away houses and claiming hundreds of lives.  

Indian Ocean Tsunami: A tectonic example

Christmas holidays in 2004 were shaped by one of the most catastrophic events in recent years, where tectonic events were at play. The trigger in this situation on the 26th of December was a rupture at the Indian-Australian plate boundaries. This event resulted in a 9.2 magnitude quake. Due to the large magnitude of the quake, a tsunami, followed by several aftershocks, reached the coasts of Indonesia, Thailand, Sri Lanka, India, and South Africa. With nearly 230,000 lives claimed, the events of 2004 resulted in international cooperation programs to monitor earthquake and volcano activity. Find more information about the program at UNDRR. 

Martigny and the Griéto glacier: A historical perspective of rapid climate change

In 1818, as a consequence of rapid global cooling, the Giétro glacier in the canton of Valais advanced proportionally (Fig.04). This glacier created a 2 km-long lake behind it, with a height of 60 m. The warming of the glacier resulted in its melting and a catastrophe that cost tens of loss of lives. The water released into the valley amounted to 20,000,000 m3, which removed everything on its way. This catastrophe was commemorated on the 100th anniversary of its occurrence and is a reminder of the importance of geological risk assessment and of the drastic consequences that climate change can have on human populations. More information is available (in French) here. 

Fig.04: Image of the Giétro glacier, as a commemoration of its dramatic melting in 1818 (gietro1818.ch).

3. Challenges of this issue 

Because of their short to nearly instantaneous timescale, rapid changes in climate or tectonics have impacts on our human timescale. It is, therefore, crucial to understand the involved processes and their intensities.

The latest publication from the Intergovernmental Panel on Climate Change (IPCC Sixth Assessment Report, August 2021) is using different models with scenarios that allow forecasting the Earth’s climate in the coming decades (Fig.05). For example, mean surface temperatures are said to increase by 1.4°C to 4.4°C until 2100. This is a huge raise, which occurs during a single humans’ lifetime!  Our Planet Earth is a cohesive machine, with interconnected elements, not only temperatures but precipitation, ocean aridity, winds, etc. As we humans are a powerful part of this machine and our life circumstances are dependent on it, we should take the responsibility of finding a solution to stop anthropogenic-induced environmental and climatic changes. 

Fig.05: Predictive map of the change in precipitation rates in the case of a mean 3°C warming (interactive-atlas.ipcc).

At this point, geology comes into play: the remains of climatic changes that are stored within the Earths’ geological record help us to determine their time-related occurrence and intensities, as well as to understand the accompanying regional consequences. Anticipating changes in precipitation will help us improve our risk assessment of extreme flood events. Forecasting sea-level rise will allow us to relocate populations before it’s too late. Studying seasonal temperatures should help understand wildfires’ repartition. Even though no past climatic event will happen twice in an identical way, each of them brings crucial information on how Planet Earth reacts to rapid disruption of its equilibrium. The better we understand it, the more efficient our adaptation will be.

If you have any questions about the dynamics of these slow processes in the source-to-sink systems, please leave a comment below! Thank you for reading and see you next month for the next post!

References:

Masson-Delmotte, V., Zhai, P., Pirani, A., Connors, S.L., Péan, C., Berger, S., Caud, N., Chen, Y., Goldfarb, L., Gomis, M.I., Huang, M., Leitzell, K., Lonnoy, E., Matthews, J.B.R., Maycock, T.K., Waterfield, T., Yelekci, O., Yu, R. and Zhou, B. (2021). Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press

Romans, B. W., Castelltort, S., Covault, J. A., Fildani, A. and Walsh, J. P. (2016). Environmental signal propagation in sedimentary systems across timescales. Earth-Science Reviews, vol.153, 7-29.