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Volcano fieldwork
As an Earth sciences student, I had the opportunity to undertake a final year project (aka the dreaded dissertation) in the field of volcanology - specifically looking at the water content of pyroclastic obsidian from the volcanic island of Lipari, Italy. This project involved 2 1/2 weeks of fieldwork in Lipari last summer, the experience of which I have documented here: http://lipariadventures.tumblr.com/
Snowflake Obsidian
Obsidian is arguably one of the most amazing and fascinating volcanic rocks on the planet. It is both relatively hard and brittle, and when it breaks it produces conchoidal (smooth, curved) fractures with very sharp edges (3 nm cutting edge). Obsidian is composed of more than 70 weight percent SiO2 (silicon dioxide), with little to no crystals. Volcanologists are still trying to figure out how exactly obsidian forms, because the process is much more complicated than magma cooling very rapidly so that crystals have no time to grow. It also has to do with the amount of water and gas in the magma, and the way in which gas is released from the magma, as obsidian contains very few or no vesicles or bubbles. It is commonly found in rhyolitic lava flows and to a lesser extent in silicic explosive eruptions (i.e. eruptions that produce pumice and ash).
Keep reading
CAVE STREAM: The name says it all. Situated amongst the Karst topography (limestone outcrop) in Canterbury, NZ, is a 594m long underground cave which, you guessed it, has a stream flowing through it. The cave was formed slowly, with slightly acidic water dissolving the limestone over time. Where the stream once flowed is still very clear, leaving a small dry valley upstream (you can almost see the valley in the bottom right of the 2nd image). You can go through the cave - just remember a bright torch and a warm wetsuit (and be careful of the eels!) In the second photo you can see the exit of the cave. The cave is home to the Cave Harvestman, a spider that is known to live only in that cave and one other on the West Coast. -MJA Reference/Further Reading: http://bit.ly/1Fu0Udw Image credits: Marcus Arnold.
Melissani Lake in Kefalonia, Greece. The lake formed in a limestone cave that was formed by dissolution of the rock, and the roof of the cave has since collapsed - creating a rather popular tourist attraction.
A rather rare geological phenomena occurs here- the lake is at the end of a drowned karst system - a system of caves in the limestone that run right through the island that have since been inundated with water as sea-level has risen. This means that the water that feeds Melissani Lake is Brackish - a mixture of salty and fresh water - and very cold because it’s originated at the sea on the other side of the island and has passed through mountains before emerging. Experiments with dye in the 1960s ascertained that the water takes on average 12 days to travel from the sinkhole in Argostoli harbour where the sea water enters the system to Melissani.
All in all a very interesting place, and a beautiful afternoon out in Kefalonia.
An Underwater Waterfall? The Island of Mauritius in the Indian Ocean hosts a truly remarkable sight. Just off the coast there appears to be an underwater waterfall. This phenomenon is most prominent when looked at from an aerial view, as in this image. Now, fluid dynamics can produce some wondrous effects, but, is cold dense water responsible for this phenomenon? Nope, but there’s still a cool explanation which delves into the topography of the sea floor. Mauritius is located at the southern edge of the Mascarene Plateau, a prominent shelf which can be seen in this image. The depth of the water above the shelf ranges from around 8-150 metres. However, where that shelf ends, there is a massive plunge into the Ocean depths. How massive? We’re talking from going from 150 metres to many thousands of metres. What you’re witnessing, that looks like an underwater waterfall, is actually sand from the shores of Mauritius being driven via ocean currents off of that high, coastal shelf, and down into the darker ocean depths off the southern tip of the island. -Jean
Underwater Waterfall?
Mauritius is an island just off the coast of Africa, close to Madagascar and Mozambique. With its stunning beaches, jewel-toned lagoons and spot of multi-colored earth, we rightly declared it one of the most beautiful islands in the Indian Ocean.
Mauritius has something even more rare — an optical illusion that makes it look like there’s really an underwater waterfall WITHIN THE OCEAN! Science easily explains that, in reality, there’s no such waterfall, just the impression of one as sand and silk sink farther into the sea, from one coastal shelf to a much, much deeper one off the southernmost part of Mauritius.
Originally from the Huntington Post
Turbidites! These rock layers may not look that distinctive, but to geologists these tell a really cool story. These are turbidites, the remnants of debris flows off the shore of an ancient ocean. Turbidites form when sediment piles up just off of a shoreline, often carried to the area by a river. Eventually, even underwater, big enough piles of sediment will collapse and avalanche downslope. Sometimes they do so under their own weight, sometimes an earthquake will set them off. The avalanche of debris produces a recognizable pattern to geologists. The heaviest particles, the biggest grains, settle out at the bottom of the debris flow, and the sequence “fines upward”, meaning the grain sizes get smaller. A typical turbidite will start at the bottom with sandy grains, maybe even larger stuff, and the grain size will decrease going upward as progressively finer grains settle out. Finally, each turbidite is topped by a layer of very fine grained clay particles that can even be a different color from the stuff below it. This sequence even has a name – the “Bouma” sequence. Turbidites show up throughout the geologic record because they’re easily preserved. They form in areas in the ocean that aren’t likely to be eroded and they form in areas with lots of sediment that can bury and protect them afterwards. This sequence photographed here is about 10 separate turbidites; the whole outcrop probably has a lot more. -JBB Image credit: Brian Romans (Creative commons): https://www.flickr.com/photos/bromans/4969233953 Read more: https://courses.washington.edu/sicilia/pdf/JBturbidites_fans.pdf http://trg.leeds.ac.uk/
ROCKS IN KNOTS These Oligocene carbonate sediments exposed on the Ionian Island of Antipaxos are, to put it politely, deformed. Rock deformation generally requires the immensity of tectonic forces (including pressure and heat) to fold, buckle, stretch and distort rocks into bizarre contortions – if you try picking up a brick, for example, and pushing and shoving it into a fold, and you’ll quickly find out that you lack the power and tenacity of a tectonic plate. There are, however, conditions in which folds can form on the Earth’s surface relatively easily. And this is what happened at Antipaxos. These are syn-sedimentary slump folds, meaning, they were formed by the deformation of these strata while they were still, essentially, mud on the bottom of the Oligocene sea. When these layers of muds were deposited on a slope, some small trigger (such as an earthquake) added just enough force for them to detach, and start sliding down slope – sort of a sub aquatic avalanche of slippery sediments. The sediments were in the initial stages of lithification, strong enough to hold together, but mushy enough to fold. In sliding downwards, they deformed, they rotated, they became a true mess, even as in this outcrop, looking as if they’re in knots. Note: In addition to this amazing slump fold, geologic interests for the traveler to Antipaxos include numerable maritime caves with arched entrances, a vertical rock spire jutting out of the Ionian, excellent beaches for sand analyses, and some very remarkable local wines… Annie R Photo by Maki Doukouros, a talented amateur photographer of Greece http://users.uoa.gr/~vkarak/pdf/34.pdf is an excellent paper on the formation of this slump system by V. Karakitsios, M. Triantaphyllou, and P. Panoussi
Beach cusps are arc-like patterns of sediment that appear on shorelines around the world. Cusps consist of horns, made up of coarse materials, connected by a curved embayment that contains finer particles. They are regular and periodic in their spacing and usually only a few meters across. A couple of theories exist as to how cusps form, but once they do, they are self-sustaining. When an incoming wave hits a horn, the water splits and diverts. The impact of the wave on the horn slows the water, causing it to deposit heavy, coarse particles on the horns while finer sediment gets carried up to the embayment before the wave flows back outward. (Photo credit: L. Tella; inspired by E. Wiebe)
Yukon river delta, Alaska.
Photograph by Jay Dickman
On 5 December, Martin Siegert, a glaciologist at the University of Bristol, and his team, will drill straight down into the Antarctic ice sheet to reach the pristine Lake Ellsworth that lies beneath.
In its shadowy waters they hope to find forms of life that have not seen the light of day in millions of years. In the lake bed sediments, the team will search for records of the poorly understood history of the West Antarctic Ice Sheet, potentially revealing how the mighty glacier has waxed and waned over time.
Last week officials opened the Glen Canyon Dam’s bypass tubes to release a simulated flood on the Colorado River, which runs through the Grand Canyon. This is the first of several planned “high-flows” intended to imitate the positive effects of natural floods on the area. Officials hope the increased water flow will help deposit sediment along the Grand Canyon’s walls at heights unreachable at the lower water levels. This sediment transport should help restore the natural sandbars and beaches that serve as breeding grounds for native fish. The floods will also clear vegetation from the riverside camping spots utilized by tourists. (Photo credit: Reuters/Bob Strong; submitted by Bobby E.)
One year ago the Elwha and Glines Canyon Dams started to be removed as part of the watershed restoration on Washington’s Olympic peninsula. It is the largest dam removal in the history of the USA. The dam removal will restores ecosystems in the long term, it will open up the river to migrating fish for the first time in 100 years and allow the river to transport sediment throughout its reach, helping to rebuild the natural bed structure and flow of the Elwha all the way to the sea by rebuilding beaches that today are starved for sand and other fine material. In the short term, excess turbidity remains the biggest concern during the next 3–10 years. About 600 dams have been taken down in the U.S. over the past 50 years, but none involved so much sediment (24 million cubic yards).
In the case of the Elwha, Congress authorized the dam removal 20 years ago, but it took two decades to get the money and logistical details in place.
Source 1, 2, 3
Moeraki boulders are found along the coast of New Zealand between Moeraki and Hampden. As you can see they are very large and rather spherical with over two thirds having a diameter of over 1.5m. Many of you will be thinking to yourself this must be erosion making these boulders so round, however although this does indeed aid slightly to the smoothness once formed this is not how the Moeraki boulders obtain their roundness to begin with. Moeraki boulders are concretions (precipitation of mineral cement within spaces between sediment grains) formed from the cementation of the Paleocene marine mud of the Moeraki formation. The process is not dissimilar to the formation of oyster pearls, the difference being Moeraki boulders formed over millions of years allowing for such an immense sizes to form. This process is not unique to New Zealand and similar specimens can be found in other parts of the world such as Rock City, Kansas where they can reach up to 6m in diameter and Lake Huron near Kettle point, Ontario, where they are referred to as “Kettles”. -Matt J photo: http://oneclickfun.blogspot.co.uk/2011/12/moeraki-boulders-newzealand-rare-photos.html More info: https://www.facebook.com/photo.php?fbid=395324987195218&set=a.352867368107647.80532.352857924775258&type=1&theater
Amazing/Surreal Bodies of Water
Caño Cristales / The River of Five Colors - Meta, Colombia
The Underwater Waterfall Illusion - Mauritius Island
Pamukkale Hot Springs - Denizle, Turkey
Plitvice Lakes - Karlovac County, Croatia
Thor’s Well - Cape Perpetua, Oregon
Sea of Stars - Vaadhoo Island, Maldives
Lake Hillier - Recherche Archipelago, Australia
The Grand Prismatic Hot Spring - Teton County, Wyoming
RIVER MEANDERING Ever have one of those “ couldn’t the river have saved a few thousand years by going just one way” thoughts? As it turns out, the reason why is the spectacular process known as river meandering. The Juruá River in the Amazon is a fantastic example of a meandering river, where a series of erosion and sediment deposition events leave a river winding and bending like a snake. Why does this happen? Meandering rivers are asymmetrical. The water on the outside edge of a river bend is deeper than the water on the inside, and also has a force created on it due to its change of direction. This water along the outside edge is constantly eroding the land on what is called the “cut bank” of the river bend. This eroded material (largely smaller particles, but still dependent on the river) is deposited on the inside bend, called the “point bar”, where water is moving more slowly. This continuation of erosion and deposition leads to exaggeration of the bend, creating the large, elaborate bends we see on so many rivers, like the pictured Juruá River. Eventually, when the bends become extreme enough, a large storm event may cause the river to “jump” from one side of the bend to another, essentially straightening the river again. This also isolates the water that had been present in the bend at the time of the jump, leaving what is known as an “oxbow lake”. The presence of these lakes can be a fantastic indicator for scientists of the history of a certain river, how quickly it meanders, and how frequently it forms oxbow lakes. Regardless of the science, though, meandering rivers are still awesomely cool to look at. -BN Photo Credit: http://www.esa.int/esaEO/SEMSDONW91H_index_0.html Further Reading: http://pages.uoregon.edu/millerm/meander.html http://www.barransclass.com/phys1090/circus/MorrisJ/MorrisJ.html
Students' reactions when I say you can tell a lot about a sedimentary rock by its texture in your mouth
