GeoLog

Geomorphology

Imaggeo on Mondays: the remotest place on Earth?

Imaggeo on Mondays: the remotest place on Earth?

Perhaps a bold claim, but at over 4,000 km away from Australia and 4,200 km from South Africa, Heard Island is unquestionably hard to reach.

The faraway and little know place is part of a group of volcanic islands known as HIMI (comprised of the Heard Island and McDonald Islands), located in the southwest Indian Ocean. Shrouded in persistent bad weather and surrounded by the vast ocean, Heard Island, the largest of the group, was first sighted by the merchant vessel Oriental in 1853.

Its late discovery and inaccessibility mean Heard Island is largely undisturbed by human activity (some research, surveillance, fishing and shipping take place on the island and it’s surrounding waters). It boasts a rich fauna and flora: seals, invertebrates, birds and seals call it home, as do hardy species of vegetation which grow low to the ground to avoid the fierce winds which batter the island.

Geologically speaking the islands are pretty unique too. They are the surface exposure of the second largest submarine plateau in the world, the Kerguelen Plateau. Limestones deposited some 45–50 million years ago began the process which saw the emergence of the islands from the ocean floor. Ancient volcanic activity followed, accumulating volcanic materials,  such as pillow lavas and volcanic sediments, up to 350m thick. For the last million years (or less) Heard Island has been dominated by volcanism, giving rise to the 2745m tall Big Ben and 700m tall Mt. Dixon. Eruptions and volcanic events have been observed on the island since 1947. Much of the recent volcanism in the region has centered around McDonald island, which has grown 40 km in area and 100 m in height since the 1980s.   

As the group of islands provides a remarkable setting, where geological processes and evolution (given that large populations of marine birds and mammals numbering in the millions, but low species diversity) can be observed in in real time, UNESCO declared HIMI a World Heritage Site back in 1997.

If you pre-register for the 2017 General Assembly (Vienna, 22 – 28 April), you can take part in our annual photo competition! From 1 February up until 1 March, every participant pre-registered for the General Assembly can submit up three original photos and one moving image related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at http://imaggeo.egu.eu/photo-contest/information/.

Geosciences Column: Do coastlines have memories?

do coastlines have memories

Did you know that the shape of coastlines is determined by the angle at which waves crash against the shoreline. It has long been thought that fluctuations in the wave incidence angle are rapidly felt by coastlines, which change the shapes of their shores quickly in response to shifting wave patterns.

Or do they?

Researchers at the British Geological Survey, Duke University (USA) and Woods Hole Oceanographic Institution in Massachusetts, have performed experiments which show that spits and capes hold ‘a memory’ of their former shapes and past wave climates, influencing their present geomorphology. The findings have recently been published in the EGU’s open access journal Earth Surface Dynamics.

Gradients in sediment distribution within wave-driven currents and shoreface depth play an important role in shaping coastlines. But the angle between an offshore wave crest and the shoreline is chief among the parameters which shape coasts worldwide.

Low-angle waves – those with approach the coast at an angle of 45° or less – have a smoothing effect on the coastline and keep its shape relatively steady. On the other hand, high-angle waves – those with slam against the shore at an angle of 45° or more – introduce instability and perturbations which shape the coast.

The figure shows the experimental set-up used in the study. It also nicely illustrates how coastlines are shaped by the angle of the incoming wave. The arrows indicatenet flux direction under waves incoming from the left; arrow lengths qualitatively indicate the flux. Sand is not transported through cells which are in shadow for a particular wave. From C. W. Thomas et al., 2016.

Alterations to the patterns of shorelines are caused by enhanced erosion and/or deposition, driven by changes in wave climate. Ultimately, coastline geomorphology evolves depending on the relative degree of high and low-angle waves in the wave climate, as well as the degree of irregularity in the wave angle distribution.

Climate change will alter the wave climate, particularly during storm events, so we can expect shorelines to shift globally. Predicting how coastlines will adapt to changing climatic conditions is hard, but more so if coastlines retain a memory of their past shapes when responding to changing wave regimes.

Flying spits (finger-like landforms which project out towards sea from relatively straight shoreline) and cuspate capes (a triangular shaped accumulation of sand and shingle which grows out towards sea) are particularly susceptible to climate change. They form when high angle waves approach the shore at a slant. Animal communities living within fragile marine and estuarine ecosystems largely depend on the protection they offer. They are also of socio-economic importance as many shelter coastal infrastructures. Understanding how they will be affected by a changing climate is vital to develop well-informed coastal management policies.

To understand how changing wave climates affect the evolution of flying spits and cuspate capes (from now on referred to as spits and capes), the team of researchers devised experiments which ran on a computer simulation.

They generated an initially straight shoreline and set the wave conditions for the next 250 years (which is the length of time it takes in nature) to allow the formation of spits and capes.

To test whether pre-existing coastal morphologies played a role in shaping coastlines under changing wave climates, over a period of 100 years (which is loosely the rate at which climate change is thought to be occurring under anthropogenic influences), the scientists gradually changed the angle at which waves approached the coast.  After the 100 year period the simulation was left to run a further 650 years under the new wave conditions.

The investigation revealed that when subjected to gradual changes in the angle at which waves approach the shoreline, capes take about 100 years to start displaying a new morphology. The tips of the capes are eroded away and so they slowly start to shrink.

Spits adjust to change much more slowly. Even after 750 years the experimental coastlines retain significant undulations, suggesting that sandy spits retain a long-term memory of their former shape.

Snapshots of simulated coastline morphologies evolved under changing wave climate. U is the fraction of waves which are approaching the shoreline at 45 degress or higher. Coastlines evolved for 250 years under initial conditions. (aii, bii)> The U values of the changed wave climate show the coastline morphologies evolved 200 and 500 years after the wave climate is changed at 250 years, and the morphologies evolved over 1000 years under static wave climates with the same U. From C. W. Thomas et al., 2016. See paper for full image caption. Click to enlarge.

The implications of the results are far reaching.

Be it implicitly or explicitly, many studies of coastal geomorphology assume that present coastal shape is exclusively a result of present wave climate. The new study shows that even with steady wave climate conditions at present, coastline shapes could still be responding to a past change in wave climate.

Reconstructions of ancient coastal geographies and paleo-wave climates might also be approached differently from now on. The researchers found that as spits adjust to changing wave climates they can leave behind a complex array of lagoons linked by beach bridges. Though there are a number of process which can lead to the formation of these coastal features, researchers must also consider alterations of coastlines as a response to changing wave climate from now on.

The findings of the study can also be applied to the management of sandy coastlines.

Currently, forecasts of future shoreline erosion and sediment deposition are made based on observations of how coasts have changed in recent decades. The new study highlights these short observation timescales may not be enough to fully appreciate how our beaches and coasts might be reshaped in the future.

This is especially true when it comes to climate change mitigation. Decisions on how to best protect the world’s shores based on their environmental and socio-economic importance will greatly benefit from long-term monitoring of coastal geomorphology.

But more work is needed too. The experiments performed by the team only consider two types of coastline morphology  (spits and capes) and only two types of wave climate. While the experiments provide a time-scale over which spits and capes might be expected to change, other factors not considered in the study (wave height, shoreface depth, etc…) will alter the predicted timescales. The time-scales given by the study should be used only as a guideline and highlight the need for more research in this area.

 

By Laura Roberts Artal, EGU Communications Officer

 

References

Thomas, C. W., Murray, A. B., Ashton, A. D., Hurst, M. D., Barkwith, A. K. A. P., and Ellis, M. A.: Complex coastlines responding to climate change: do shoreline shapes reflect present forcing or “remember” the distant past?, Earth Surf. Dynam., 4, 871-884, doi:10.5194/esurf-4-871-2016, 2016.

Imaggeo on Mondays: Tones of sand

Tones of Sand

With rocks dating as far back as the Precambrian, mountain building events, violent volcanic eruptions and being covered, on and off, by shallow seas, Death Valley’s geological history is long and complex.

Back in the Cenozoic (65 to 30 million years ago), following a turbulent period which saw the eruption of volcanoes (which in time would form the Sierra Nevada of California) and regional uplift, Death Valley was a peaceful place. There was no deposition of sediments, nor emplacement of igneous rocks. The valley was being eroded, slowly.

Fast forward a few thousand years, to the Miocene (ca. 27 million years ago) and all that changed. New volcanic eruptions drove the onset of a major extensional event, which saw basins and ranges develop into Death Valley as we know it today.

The tectonics of the region were also complex: the North American plate was riding up and over the Pacific plate, but around the same time as the extension started in the basin, the spreading centre of the Pacific plate intersected with the Fallon Plate, splitting it in half. The northern section became the Juan de Fuca plate and the San Andreas Fault was created between the remnants of the subduction zone.

The Panamint Range – a fault-block mountain range on the edge of the Mojave Desert – formed as a result of the powerful tectonic events. Initially, it rode over and piggy backed on top of The Black Mountains, before sliding towards the west.  As the mountain ranges slid apart, the valleys lost height too and started receiving sediment.

The sediment influx happens to this day, as evidenced in today’s Imaggeo on Monday’s photograph, taken by Marc Girons Lopez, a hydrologist at Uppsala University (Sweden).

“The photograph was taken from Dante’s View viewpoint terrace and shows the Death Valley on the foreground and the Panamint Range on the background,” describes Marc.

At present, a series of alluvial fans drain the Panamint Range, forming triangle-shaped deposits of gravel, sand and silt. These fans are formed through the deposition of sediments eroded from the Panamint Range during flash flood events.

Marc says that “the colour of the sand forming the alluvial fans relates to their age; the clearer the tones the younger their age.”

The salt flats in the foreground, which are covered in salt and other minerals, are the remnants of Lake Manly, a landlocked lake system which drained to no other bodies of water such as rivers or oceans. The lake was present during the Pleistocene era (2.85 million years ago) and slowly evaporated as the region progressively desertified. The evaporitic salts have been exploited in modern times.

 

If you pre-register for the 2017 General Assembly (Vienna, 22 – 28 April), you can take part in our annual photo competition! From 1 February up until 1 March, every participant pre-registered for the General Assembly can submit up three original photos and one moving image related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at http://imaggeo.egu.eu/photo-contest/information/.

The best of Imaggeo in 2016: in pictures

The best of Imaggeo in 2016: in pictures

Imaggeo, our open access image repository, is packed with beautiful images showcasing the best of the Earth, space and planetary sciences. Throughout the year we use the photographs submitted to the repository to illustrate our social media and blog posts.

For the past few years we’ve celebrated the end of the year by rounding-up some of the best Imaggeo images. But it’s no easy task to pick which of the featured images are the best! Instead, we turned the job over to you!  We compiled a Facebook album which included all the images we’ve used  as header images across our social media channels and on Imaggeo on Mondays blog post in 2016 an asked you to vote for your favourites.

Today’s blog post rounds-up the best 12 images of Imaggeo in 2016, as chosen by you, our readers.

Of course, these are only a few of the very special images we highlighted in 2016, but take a look at our image repository, Imaggeo, for many other spectacular geo-themed pictures, including the winning images of the 2016 Photo Contest. The competition will be running again this year, so if you’ve got a flare for photography or have managed to capture a unique field work moment, consider uploading your images to Imaggeo and entering the 2017 Photo Contest.

Blue Svartisen . Credit: Kay Helfricht (distributed via imaggeo.egu.eu)

When you think of a glacier the image you likely conjure up in your mind is that of bright white, icy body. So why do some glaciers, like Engabreen, a glacier in Norway, sometimes appear blue? Is it a trick of the light or some other phenomenon which causes this glacier to look so unusual?  You can learn all about it in this October post over on GeoLog.

 

‘There is never enough time to count all the stars that you want.’ . Credit: Vytas Huth (distributed via imaggeo.egu.eu). The centre of the Milky Way taken near Krakow am See, Germany. Some of the least light-polluted atmosphere of the northern german lowlands.

Among the winning images of our annual photo contest was a stunning night-sky panorama by Vytas Huth; we aren’t surprised it has been chosen as one of the most popular images of 2016 too. In this post, Vytas describes how he captured the image and how the remote location in Southern Germany is one of the few (in Europe) where it is still possible to, clearly, image the Milk Way.

 

“Above the foggy strip, this white arch was shining, covering one third of the visible sky in the direction of the ship's bow,” he explains. “It was a so-called white, or fog rainbow, which appears on the fog droplets, which are much smaller then rain droplets and cause different optic effects, which is a reason of its white colour.”

Gateway to the Arctic . Credit: Mikhail Varentsov (distributed via imaggeo.egu.eu)

“Above the foggy strip, this white arch was shining, covering one third of the visible sky in the direction of the ship’s bow,” describes Mikhail Varentsov, a climate and meteorology expert from the University of Moscow. “It was a so-called white, or fog rainbow, which appears on the fog droplets, which are much smaller then rain droplets and cause different optic effects, which is a reason of its white colour.” Mikhail captured the white rainbow while aboard the Akademik Tryoshnikov research vessel during its scientific cruise to study the effects of climate change on the Arctic.

 

History. Credit: Florian Fuchs (distributed via imaggeo.egu.eu)

The header image, History by Florian Fuchs, we used across our social media channels was popular with our Facebook followers, who chose it as one of the best of this year. The picture features La Tarta del Teide – a stratigraphic section through volcanic deposits of the Teide volcano on Tenerife, Canary Islands.

 

Find a new way . Credit: Wolfgang Fraedrich (distributed via imaggeo.egu.eu)

Lavas erupted into river waters, and as a result cooled very quickly, can give rise to fractures in volcanic rocks. They form prismatic structures which can be arranged in all kinds of patterns: horizontally (locally known as the woodpile), slightly arching (the harp) and in a radial configuration known as the rosette. The most common configuration is the ‘organ pile’ where vertical fractures form. These impressive structures are seen in the walls of the Gole dell ‘Alcantara, a system of gorges formed 8,000 years ago in the course of the river Alcantara in eastern Sicily.

 

Home Sweet Home . Credit: André Nuber (distributed via imaggeo.egu.eu)

Can you imagine camping atop some of the highest mountains in Europe and waking up to a view of snowcapped peaks, deep valleys and endless blue skies? This paints an idyllic picture; field work definitely takes Earth scientists to some of the most beautiful corners of the planet.

 

Isolated Storm . Credit: Peter Huber (distributed via imaggeo.egu.eu)

In November 2016 we featured this photograph of an isolated thunderstorm in the Weinviertel in April. The view is towards the Lower Carpathian Mountains and Bratislava about 50 kilometers from Vienna. Why do storms and isolated thunderstorms form? Find out in this post.

 

Glacial erratic rocks . Credit: Yuval Sadeh (distributed via imaggeo.egu.eu)

As glaciers move, they accumulate debris underneath their surface. As the vast frozen rivers advance, they carry the debris, which can range from pebble-sized rocks through to house-sized boulders, along with it. As the climate in the Yosemite region began to warm as the ice age came to an end, the glaciers slowly melted. Once all the ice was gone, the rocks and boulders, known as glacial erratics, were left behind.

 

Snow and ash in Iceland . Credit: Daniel Garcia Castellanos (distributed via imaggeo.egu.eu)

Icelandic snow-capped peaks are also sprinkled by a light dusting of volcanic ash in this photograph. Dive into this March 2016 post to find out the source of the ash and more detail about the striking peak.

 

Living Flows . Credit: Marc Girons Lopez (distributed via imaggeo.egu.eu)

There are handful true wildernesses left on the planet. Only a few, far flung corners, of the globe remain truly remote and unspoilt. To explore and experience untouched landscapes you might find yourself making the journey to the dunes in Sossuvlei in Namibia, or to the salty plain of the Salar Uyuni in Bolivia. But it’s not necessary to travel so far to discover an area where humans have, so far, left little mark. One of the last wilds is right here in Europe, in the northern territories of Sweden. This spectacular photograph of the Laitaure Delta is brought to you by Marc Girons Lopez, one of the winners of the 2016 edition of the EGU’s Photo Contest!

 


The power of ice. Credit: Romain Schläppy, (distributed via imaggeo.egu.eu).

The January 2016 header image across our social media was The Power of Ice, by Romain Schlappy. This vivid picture was captured from a helicopter by Romain Schläppy during a field trip in September 2011. You can learn more about this image by reading a previous imaggeo on mondays post.

 

Sea of Clouds over Uummannaq Fjord. Credit: Tun Jan Young (distributed via imaggeo.egu.eu)

The current header image, Sea of Clouds over Uummannaq Fjord by Tun Jan Young, is also a hit with our followers and the final most popular image from Imaggeo in 2016. A sudden change of pressure system caused clouds to form on the surface of the Uummannaq Fjord, Northwestern Greenland, shrouding the environment in mystery.

 

If you pre-register for the 2017 General Assembly (Vienna, 22 – 28 April), you can take part in our annual photo competition! From 1 February up until 1 March, every participant pre-registered for the General Assembly can submit up three original photos and one moving image related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at http://imaggeo.egu.eu/photo-contest/information/.

 

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