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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: Giants Causeway

Imaggeo on Mondays: Giants Causeway

Since its discovery back in the late 1600s the origin of the spectacular polygonal columns of the Giants Causeway, located on a headland along the northern coast of Ireland, has been heavily debated. Early theories for its origin ranged from being sculpted by men with picks and chisels, to the action of giants, through to the force of nature. It wasn’t until 1771 that Demarest, a Frenchman, suggested that the origin of the world-famous headland was indeed volcanic.

“The myth goes that the Irish giant Finn MacCool once constructed a land bridge from Northern Ireland to Scotland in order to meet a rival giant,“ explains Bernhard Aichner, author of this week’s featured imaggeo image. “It is said that he used basaltic rocks from the surrounding cliffs to construct the bridge. Finn´s rival later destroyed most of the causeway, but the remnants still can be seen today as basalt columns descending into the sea.“

We now know that the hexagonal columns along the rugged Irish coastline formed some sixty million years ago, during a time when the ancestors to modern plant species started to emerge and the Earth was going through a period of warming. At the time, Antrim (a modern-day county of Ireland), was subjected to an intense period of volcanic activity as a result of the opening of the Atlantic Ocean.

The Giants Causeway is only a small part of a vast network of lava flows which extended over the Antrim landscape; much of which, through the passage of time, has been eroded away. There were three distinct periods of volcanic activity which resulted in a thick succession of lava flows which has been subdivided into the Lower, Middle and Upper Basalts.

The lavas of the Giants Causeway belong to the Middle Basalts and comprise over 40,000 vertical columns. Recently, a new model was proposed for the formation of the striking polygonal pattern formed by the columns. They formed within a lava flow, which contracted and fractured while cooling very slowly. If the loss of heat is steady, then the pattern formed is uniform, but if areas cool faster than others, the fractures develop unevenly, meaning the columns form in a variety of sizes and shapes: expect anything from pentagons to heptagons if you get a chance to visit the Causeway!

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: Fresh breakout in the lava fields

Fresh Breakout in the lava fields. (Credit: Kate Dobson via imaggeo.egu.eu)

Fresh Breakout in the lava fields. (Credit: Kate Dobson via imaggeo.egu.eu)

Kate Dobson was a volunteer at the Hawaii Volcano Observatory (HVO) in 2001/02 and revisited the stunning Big Island in 2006. During her holidays Kate ventured out to the coastal section of the Pu’uO’o lava flow field and captured this spectacular image of a fresh lava breakout.

The Pu‘u ‘Ō‘ō vent is in the East Rift Zone of Kīlauea Volcano and began erupting on January 3, 1983, and has continued to do so for more than 31 years, with the majority of lava flows advancing to the south. The original eruptions during the early 1980s were typically short lived and characterised by the eruption of viscous and slow moving a’a’ lava flows. However, in 1986 the eruption shifted to Kupaianaha, 3 km to the northeast of the original eruption site, and the eruption style changed significantly. A quiet, but continuous eruption of pahoehoe lava followed, snaking its way down the pali (steep costal slopes) and coastal plains to eventually reach the ocean. This extensive succession of lava flows damaged areas of Kapa’ahu village and closed the coastal highway.

The breakout pictured in our Imaggeo on Mondays image (taken more recently, in 2006 but probably resulting from similar to the activity described above) “is approximately 60cm and is sourced from an inflating basaltic flow which I photographed from a few metres away” explains Kate, “ I was about 300m inland from the ocean entry, and about 4 miles (800m elevation drop) from the source vent at Pui’u O’o.” The entry of the lava into the ocean creates spectacular columns of steam which attract numerous tourists. Whilst the HVO and the Hawaii Volcanoes National Park staff try hard to restrict viewing of the spectacular natural display, curiosity often gets the best of people as Kate describes “ I had just stopped three poorly equipped tourists (trainers, no water, no sunscreen) from blundering onto the active area a little further upstream and was heading back towards the ocean when the break out happened”.

Lava flow entering the sea on SE coast of Hawaii. Hawaii, Hawai (Credit: HVO,  U.S. Department of Interior, U.S. Geological Survey)

Lava flow entering the sea on SE coast of Hawaii. Hawaii, Hawai (Credit: HVO, U.S. Department of Interior, U.S. Geological Survey)

Since the onset of the volcanic activity at the Pu‘u ‘Ō‘ō vent the activity has waxed and waned and has presented an ongoing threat to the local communities on the Big Island of Hawaii. Towards the end of June of this year a new lava flow started to threaten the residential area of Kaohe Homesteads and Pāhoa town in Puna. Whilst not unprecedented, what is unusual about this particular lava flow is that rather than flowing towards the southeast, the lava flow is erupting towards the northeast. Given the current rate at which the flow is advancing, scientists of the HVO expect it to reach Pāhoa town by mid-November. In the 1930s, when a lava flow threatened the large town of Hilo on the eastern coast of the Island, the then director of the HVO, Thomas Jaggar, attempted to stop the threat posed by the lava flow by bombing it! The success of the enterprise was limited but Mauna Loa stopped erupting before any major damage was caused.