GeoLog

Regular Features

Imaggeo on Mondays: A lava layer cake

Imaggeo on Mondays: A lava layer cake

Brekkuselslækur, a small river, carves its way across Iceland’s ancient volcanic landscape. At Hengifoss, Iceland’s third-highest waterfall, it tumbles fiercely down thick, dark layers of lavas erupted from volcanoes some 18 to 2.58 million years ago, during a period of geological time known as the Tertiary.

Eruptions are rarely continuous; during hiatuses in the extrusion of lavas, ash is able to settle atop the smoldering layers. If the pauses are long enough and the conditions just right (a warm and humid climate is needed) the ashes, through the addition of clay and iron minerals, slowly turn to soil . When new lavas are layered over the top of the ash-rich soils, a chemical reaction takes place between the iron trapped in the soil and the oxygen transported by the lavas, to form iron oxide. In essence, the soils rust and turn a distinctive red colour.

As the process is repeated time and time again, layers of alternating black lavas and red soils are built up to form a giant ‘mille feuilles’ cake.

In the summer months, tourists flock to this popular site. An unspoilt view of the 188m high torrent means an early morning hike to beat the crowds. For a bird’s eye view of Hengifoss, the adventurous can even scarmble to the cliff tops too.

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/.

Meet the EGU’s new Science Policy Officer

Meet the EGU’s new Science Policy Officer

Hi there, my name is Chloe and I’m embarking on a new challenge. After participating in the EGU’s 2017 General Assembly 3 weeks ago as a warmup, I am starting in Munich as the EGU’s Policy Officer. While the title might sound a little ambiguous, it is an incredibly exciting position that allows me to facilitate the dissemination of the EGU members’ scientific knowledge to EU policy-makers while simultaneously sharing upcoming political issues with EGU members.

Originally from Tasmania, I am a long way from home! However, I have lived, worked and studied in Europe for the last 6 years. After gaining an undergraduate degree in Environmental Sciences I moved onto bigger things – first to Copenhagen and then onto Germany where I undertook a Masters in Environmental Governance at the Albert-Ludwigs-Universität of Freiburg. Although working as Policy Officer with the EGU will be a new experience for me, I have gained an understanding of the science policy interface through my work with the African EU Energy Partnership, the Indo-German Centre for Sustainability and the Institute of Climate and Sustainable Cities.

I am really motivated to start working with the entire EGU team and for the challenge of facilitating science for policy activities. If you have any comments, questions or suggestions regarding science for policy, please feel free to email me at policy@egu.eu. You can also sign up to the EGU Database of Expertise if you would like to know more about the science policy process or about upcoming opportunities to share your scientific knowledge.

Imaggeo on Mondays: Sedimentary record of catastrophic floods in the Atacama desert

Imaggeo on Mondays: Sedimentary record of catastrophic floods in the Atacama desert

Despite being one of the driest regions on Earth, the Atacama desert is no stranger to catastrophic flood events. Today’s post highlights how the sands, clays and muds left behind once the flood waters recede can hold the key to understanding this natural hazard.

During the severe rains that occurred between May 12 and 13, 2017 in the Atacama Region (Northern Chile) the usually dry Copiapó River experienced a fast increase in its runoff. It caused the historic center of the city of Copiapó to flood and resulted in thousands of affected buildings including the University of Atacama.

The city of Copiapó (~160,000 inhabitants) is the administrative capital of this Chilean Region and is built on the Copiapó River alluvial plain. As a result, and despite being located in one of the driest deserts of the world, it has been flooded several times during the 19th and 20th century. Floods back in 2015 were among the worst recorded.

The effects of the most recent events are, luckily, significantly milder than those of 2015 as no casualties occurred. However, more than 2,000 houses are affected and hundreds have been completely lost.

During this last event, the water height reached 75 cm over the river margins. Nearby streets where filled with torrents of mud- and sand-laden waters, with plant debris caught up in the mix too. Once the waters receded, a thick bed of randomly assorted grains of sand  was deposited over the river banks and urbanized areas.

Frozen in the body of the bed, the sand grains developed different forms and structures. A layer of only the finest grained sediments, silts and clays, bears the hallmark of the final stages of the flooding. As water speeds decrease, the finest particles are able to drop out of the water and settle over the coarser particles. Finally, a water saturated layer of mud, only a few centimeters thick, blanketed the sands, preserving the sand structures in 3D.

The presence of these unusual and enigmatic muddy bedforms has been scarcely described in the scientific literature. A new study and detailed analysis of the structures will help better understand the sedimentary record of catastrophic flooding and the occurrence of high-energy out-of-channel deposits in the geological record.

By Manuel Abad and Tatiana Izquierdo, Universidad de Atacama (Chile)

 

Imaggeo on Mondays: Polar backbone (Arctic Ocean)

Imaggeo on Mondays: Polar backbone (Arctic Ocean)

This image was taken during the Arctic Ocean 2016(AO16) expedition that ventured to the central regions of the Arctic Ocean, including the North Pole. It shows a pressure ridge, or ice ridge, as viewed from onboard the deck of the icebreaker Oden. It was quite striking that the ice ridge resembled an image of a spine – sea ice being a defining characteristic of the broader Arctic environment and backbone to global climate interactions.

An ice ridge is a wall of broken ice that forms when floating ice is deformed by a build up of pressure between adjacent ice floes. Sea ice can drift quite quickly, and is driven by wind and ocean currents. Ridges are typically thicker than the surrounding level sea ice, being built up by ice blocks of different sizes. The submerged portion of the ridge is referred to as the “keel”, and the part above the water surface is called the “sail”. Ridges can be categorized as “first year” or “multi-year” features, with weathering affecting the morphology.

In the Arctic, such ridges have been measured to in excess of 20 m in thickness including keel and sail. As someone who studies plate tectonics, these collisional boundaries between plates of ice reminded me of a downscaled mountain-building setting.

The AO16 expedition ran from August to September 2016 and involved the Swedish icebreaker Oden and the Canadian icebreaker the Louis S. St-Laurent. A wealth of geological, oceanographic, meteorological data was collected. This period appeared to have coincided with the second lowest extent of sea ice coverage on record (tied with 2007), with around 4.14 million square kilometers.

The geological evolution of the Arctic Ocean in the regions closest to the margins of northern Greenland and the Canadian Arctic Islands are some of the most poorly understood. This is largely a function of the oceanic gyre system, which causes the thickest sea ice to build up in these areas making physical access difficult. From a maritime engineering perspective, the ice ridges pose a challenge and risk to icebreaking operations and navigation. Ice ridges may determine the design load for marine and coastal structures such as platforms, ships, pipelines and bridges, and are important for both ice volume estimations and for the strength of pack ice.

By Grace Shephard, geophysicist from the Centre for Earth Evolution and Dynamics (CEED) at the University of Oslo, Norway.

Follow

Get every new post on this blog delivered to your Inbox.

Join other followers: