GeoLog

Chile

Imaggeo on Mondays: Cordillera de la Sal

Imaggeo on Mondays: Cordillera de la Sal

The photograph shows the Valle de la Luna, part of the amazing Cordillera de la Sal mountain range in northern Chile. Rising only 200 metres above the basin of the Salar de Atacama salt flat, the ridges of the Cordillera de la Sal represent a strongly folded sequence of clastic sediments and evapourites (salt can be seen in the left portion of the image), with interspersed volcanic material.

This formation evolved when the depression between the Cordillera Domeyko mountain range and the main Andean mountain ranges, filled by an ancient salt flat, was squeezed together over the last 10-15 million years, leaving behind the folded belt of hills seen today. Sand brought along from adjacent areas by the winds was caught between the ridges of the Cordillera de la Sal, accumulating to form the impressive dune shown in the foreground of the image.

Under normal conditions, the perfectly shaped Licancabur Volcano, forming the border between Chile and Argentina, would appear in the background of this sunset scene. However, the image was taken during the Invierno Boliviano (Bolivian winter), when humid air from the eastern side of the Andes travels west across the Andean Plateau, Altiplano. The air masses journey all the way to the otherwise extremely arid Atacama Desert, bringing clouds, rain and occasionally even hail.

I have been to this area three times: first for vacation, then two times for excursions with students, most recently in February this year. Interestingly, the weather was as to be expected for the Atacama Desert only one time. For the two other times, the weather was looking like this photograph, so it is hard for me to believe that the Atacama would be as arid as people always say. However, indeed, the pieces of geological and geomorphological evidence, such as the folded layers of the Cordillera de la Sal, clearly indicate its extreme aridity, prevailing for tens of millions of years!

By Martin Mergili, University of Vienna

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: Chilean relics of Earth’s past

Imaggeo on Mondays: Chilean relics of Earth’s past

As Earth’s environment changes, it leaves behind clues used by scientists to paint portraits of the past: scorched timber, water-weathered shores, hardened lava flows. Chile’s Conguillío National Park is teeming with these kind of geologic artifacts; some are only a few years old while others have existed for more than 30 million years. The photographer Anita Di Chiara, a researcher at Lancaster University in the UK, describes how she analyses ancient magnetic field records to learn about Earth’s changing crust.

Llaima Volcano, within the Conguillío National Park in Chile, is in the background of this image with its typical double-hump shape. The lake is called Lago Verde and the trunks sticking out are likely remnants from one of the many seasonal fires that have left their mark on this area (the last one was in 2015).

The lake sits on pyroclastic deposits that erupted from the Llaima Volcano. On these deposits, on the side of the lake, you can even track the geologic record of seasonal lake level changes, as the layers shown here mark the old (higher) level of the lake during heavy winter rains.

The lake also overlaps the Liquiñe-Ofqui Fault, which runs about 1000 kilometers along the North Patagonian Andes. The fault has been responsible for both volcanic and seismic activity in the region since the Oligocene (around 30 million years ago).

I was there as field assistant for Catalina Hernandez Moreno, a geoscientist at Italy’s National Institute of Geophysics and Volcanology, studying ancient magnetic field records imprinted on rocks. We examined the rocks’ magnetised minerals (aligned like a compass needle to the north pole) as a way to measure how fragmented blocks of the Earth’s crust have rotated over time along the fault.

From this fieldwork we were able to examine palaeomagnetic rotation patterns from 98 Oligocene-Pleistocene volcanic sites. Even more, we concluded that the lava flows from the Llaima Volcano’s 1958 eruption would be a suitable site for studying the evolution of the South Atlantic Anomaly, an area within the South Atlantic Ocean where the Earth’s magnetic field is mysteriously weaker than expected.

By Anita Di Chiara, a research technician at the Lancaster Environment Centre in the UK 

References

Hernandez-Moreno, C., Speranza, F., & Di Chiara, A.: Understanding kinematics of intra-arc transcurrent deformation: Paleomagnetic evidence from the Liquiñe-Ofqui fault zone (Chile, 38-41°S), Tectonics, https://doi.org/10.1002/2014TC003622, 2014.

Hernandez-Moreno, C., Speranza, F., & Di Chiara, A.: Paleomagnetic rotation pattern of the southern Chile fore-arc sliver (38°S-42°S): A new tool to evaluate plate locking along subduction zones. Journal of Geophysical Research: Solid Earth, 121(2), https://doi.org/10.1002/2015JB012382, 2016.

Di Chiara, A., Moncinhatto, T., Hernandez Moreno, C., Pavón-Carrasco, F. J., & Trindade, R. I. F.: Paleomagnetic study of an historical lava flow from the Llaima volcano, Chile. Journal of South American Earth Sciences, 77, https://doi.org/10.1016/j.jsames.2017.04.014, 2017.

 

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submittheir 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: The unique bogs of Patagonia

Imaggeo on Mondays: The unique bogs of Patagonia

Patagonia, the region in southernmost tip of South America, is as diverse as it is vast. Divided by the Andes, the arid steppes, grasslands and deserts of Argentina give way to the temperate rainforests, fjords and glaciers of Chile. Also on the Chilean side are rolling hills and valleys of marshy topography: Patagonia’s bogs. Today, Klaus-Holger Knorr, a researcher at the University of Münster’s Institute for Landscape Ecology, tells us about what makes these peatlands so unique.

This picture shows an ombrotrophic, oceanic bog at the Seno Skyring Fjord, Patagonia, Chile. It is a view from the inner part of the peatland south toward the shore of the Fjord, in the background Isla Escapada and the Gran Campo ice field. Ombrotrophic bogs are peatlands (accumulations of more or less decomposed plant material which collect in a water-saturated environment) receiving their water and nutrients solely from the atmosphere, i.e. by rain, wet and dry deposition.

Similar to their Northern counterparts in Canada, Northern US, Fennoscandia or Siberia, these southern Patagonian peatlands  formed after the last deglaciation and accumulated huge amounts of carbon as peat.

Peatlands cover only about 3 % of the global land surface but store about a third of the soil carbon pool. Peat is formed primarily as there is excess rainfall, peat soils are water logged, oxygen gets depleted, and decomposition is limited. Pristine, undisturbed peatlands can store as much as 10-50 g carbon per square meter and year.

What makes the peatlands in Patagonia  particularly interesting  is their pristine, undisturbed conditions and extremely low input of nutrients from the atmosphere, compared to the high input into sites in densely settled or industrial regions. This allows studies of peatland functioning under natural conditions and absence of anthropogenic impacts.

Moreover, peatlands in Patagonia harbor a specific kind of vegetation, including cushion forming plants such as Astelia pumila and Donatia fascicularis. These cushion forming plants have a very low above ground biomass but an extremely large rooting system, reaching down to a depth of >2 m in case of A. pumila. As these roots act as conduits for oxygen to sustain viability of the roots in the water logged peat, they have been shown to aerate large parts even of the saturated zone, thereby impeding high methane production and emission. Oxygen supply by these roots is even hypothesized to stimulate peat decomposition and thereby lead to particularly decomposed peat under cushion plant cover.

Another plant species only occurring in peatlands of Southern Patagonia, a small conifer named Lepidothamnus fonkii, has developed a particular strategy to overcome nutrient deficiency: it has formed a close association with bacteria being able fix atmospheric nitrogen to fulfill the demand of nitrogen for growth. While such nitrogen fixation is well known for legumes and some tree species, it has rarely been found for conifers.

A further important factor for peatlands in Patagonia, leading to the term “oceanic bogs”, is the fact that these peatlands in close vicinity to the seashore receive high inputs of sea salts from sea spray, modifying availability of associated elements such as Sodium, Calcium, Magnesium, Sulphur and others.

By Klaus-Holger Knorr, researcher at the University of Münster’s Institute for Landscape Ecology

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/.

 

Shaking on Christmas Day: what we know about the 7.6 M Chile earthquake

Chile, Chiloe earthquake

While the majority of us were midway through our Christmas Day celebrations, a powerful 7.6 M earthquake struck off the western coast of the Chile. Natural hazards are not bound by time, location or festivities; an earthquake can happen at any time in any place, regardless of the significance of the day. As a result, in this earthquake prone region, raising awareness of the risk posed by natural hazards is vitally important.

The Christmas Day quake struck 42 km south west of the port city of Quellón, on the rural island of Chiloé at a depth of 34 km. Despite the powerful shaking, the tremor caused no casualties and damage to infrastructure was limited. For a time, services (such as water and power) to the southern tip of Chiloé were cut. Most affected were roads and bridges, particularly the recently renovated highway 5, which links Quellón with the fishing town of Chonchi.

The earthquake triggered a tsunami warning, leading to the evacuation of 4000 people in the coastal areas of Los Lagos Region, including the towns of Quellón and Chonchi. However, no tsunami waves were reported and the warning was lifted some 90 minutes after the temblor.

Chile’s long history of powerful earthquakes

As recently as September 2015, an 8.3 M tremor hit Illapel, causing 13 casualties, 6 missing and triggering a 4.5 m tsunami wave, with shaking felt as far as Bolivia and Argentina.

A powerful, and destructive, 8.8 M quake struck Maule in February 2010. On land, there was severe loss to infrastructure and housing, while a tsunami wave caused significant damage to coastal areas. Combined, the earthquake and tsunami resulted in the deaths of more than 500 people.

The most powerful tremor ever recorded, the estimated 9.5 M Valdivia earthquake, struck Chile in May 1960. More than 2,000 people were reported dead, a further 3,000 went missing and over 2,000,000 were left homeless. The damage in Southern Chile alone amounted to over $550 million. Tsunami waves generated by the quake struck Hawaii, Japan, the Philippines and the western USA coast, causing a further $50.5 million in damages and killing 231 people.

Damage to houses after the Valdivia earthquake, Chile

Damage to several houses in Chile after the earthquake. Credit: Pierre St. Amand – NGDC Natural Hazards Slides with Captions Header, Public Domain (distributed by Wikimedia Commons)

What causes earthquakes in Chile and what does the future hold?

Chile lies along the Pacific Ring of Fire, an area known for its high seismic and volcanic activity. Here, tectonic plates slide against each other, pull apart or converge and subduct under one another generating geologically active zones.

To understand why powerful earthquakes occur in Chile, we asked Cindy Mora Stock, a seismologist at the University of Concepción (Chile), to give us a more detailed insight into the tectonics of the region:

Earthquakes along the Chilean coast occur at the interface between the South American plate and the subducted Nazca plate. The rapid velocity between these plates (66 – 90 mm/yr) increases the potential for great earthquakes in the region, presenting on average an event of magnitude 8, or larger, every ten years. As a comparison, the Antarctic plate subducts under South American plate at a much slower rate (16 – 22 mm/yr).

The latest Mw 7.6 earthquake near Quellón on 25th of December [1], falls in the central part of the rupture zone (the portion of the fault which slipped during) of  the Valdivia earthquake – roughly 380 km south from Valdivia.

A study by Lange et al in 2007 showed a cluster of four main 4.0 < Ml < 4.4 events and their afteshocks, occurring at the interface between 12-30 km depth, beneath the western coast of Chiloe Island. Another study by Moreno et al in 2011 shows some patches at the interface that ruptured during the previous 1960 event, which are more stuck than other areas at the same interface.

Especially, computer simulations show the interface at the center part of the 1960’s rupture zone is fully locked, this means that part is “stuck”, not moving, and accumulating energy. Zones that present a high locking rate have shown to be prone areas for the nucleation of a great earthquake in the future. Although in all presented scenarios the Chiloe Island presents a high locking rate, this is not enough to state a range of time when an earthquake will occur at this patch.  Considering this, the previous seismicity, and the present Mw7.6 earthquake in the region it might seem like the interface might have ended its and it is starting to build up stress for a future earthquake.

By Laura Roberts, EGU Communications Officer, and Cindy Mora Stock, postdoctoral researcher at the University of Concepcion, Chile.

 

References and further reading

[1] Intensities of shaking felt after the 25 December earthquake (in Spanish): http://www.sismologia.cl/events/sensibles/2016/12/25-1422-28L.S201612.html

[2] Lange, D., Rietbrock, A., Haberland, E., et al.: Seismicity and geometry of the south Chilean subduction zone (41.5°S–43.5°S): Implications for controlling parameters, Geophysical Research Letters, 34, L06311, doi: 0.1029/2006GL029190, 2007

[3] Moreno, M., Melnick, D., Rosenau, M., et al.: Heterogeneous plate locking in the South–Central Chile subduction zone: Building up the next great earthquake, Earth and Planetary Research Letters, 305, 3-4, 413-424, doi: 10.1016/j.epsl.2011.03.025, 2011 (Paywalled)

USGS overview of M7.6 – 42km SW of Puerto Quellon, Chile (includes shake maps, regional tectonic information and moment tensor details): http://earthquake.usgs.gov/earthquakes/eventpage/us10007mn3#executive

Understanding Tectonic Processes Following Great Earthquakes (Eos: Earth & Space Science News)

25 December earthquake in the news:
·         Chile earthquake tsunami warning lifted (BBC News report)
·         Major quake jolts Chile tourist region on Christmas Day (Reuters in-depth news report)
·         Chile jolted by major 7.6-magnitude earthquake (Guardian News)
·         Imagenes del terremoto al sur de Chile (in Spanish: Images of the earthquake in Southern Chile – Gestión, diario de econimía y negocios de Perú)