The Earth Story

Lac Couture The hard metamorphic Archaean (3.8-2.5 billion years old) gneisses of the Precambrian Canadian shield preserve more than their fair statistical share of impact craters, since they are very resistant to erosion. The 8km diameter lake known as Couture lies in the centre of such a crater, being found in Quebec, near Hudson bay. Scientists have dated it by analysing samples of impact melt to the Silurian (around 430 million years ago), just as life was beginning to emerge onto the land. Physical evidence in the form of impact shocked minerals and shatter cones of rock abound in the area. Sited in the slightly bleak looking tundra zone, the area was covered by ice sheets during the ice ages, which planed down toe topography to its currently subdued level. The central peak is submerged under the lake's waters, and the rim has been more or less planed down. The crater was once much larger, but the erosion has only left behind the breccia (shattered rock) that underlay the original impact site. Our past posts on Canadian impact craters: Pingualuit: http://tinyurl.com/m3aj4rt Sudbury: http://tinyurl.com/masy7yd Manicouagan: http://tinyurl.com/d4osf4n Loz Image credit: Hearmusicz http://www.passc.net/EarthImpactDatabase/couture.html http://ottawa-rasc.ca/wiki/index.php?title=Odale-Articles-LacCouture

Pingualuit impact crater.

Discovered in a remote region of Northern Quebec during a USAAF meteorological flight during the second world war, and used as a navigational landmark by pilots, the impact origin of this beautiful feature wasn't established until geologists first reached it in the 1950's. It wasn't finally confirmed until tektites were found on the crater rim and down glacier from the crater.The bolide impacted around 1.4 million years ago, during the ice age, the 3.44 km diameter crater is named after the Inuktitut word for where the land rises.

The Pingualuk lake in the crater is fed by rain and snowmelt, and reaches a depth of 270 metres and its water is some of the purest on our globe. Because the lake is isolated and uncontaminated by other sediments, and the crater sediments weren't eroded by ice sheets, its sediments provide us with a good record of the many climate oscillations that happened during the advances and retreats of the ice sheets as glacial and interglacial periods alternated.

Researchers have used pollen and the silica skeletons of diatoms (a type of alga) in the sediment to chart alternations of warmer and cooler conditions, finding two layers from ice free interglacial eras. This lake us bigger than others in the region, holding its temperature longer due to the high specific heat of water. In consequence it is the last to freeze and melt in the annual cycle of the seasons. The lake also contains fish with large heads, though it is not known how they first reached it.

The crater is in a national park of the same name, in an area of bare tundra landscape. The impact uplift of the surrounding rocks is twice as large as the crater itself. Canada is one of several places that preserve better records of impact craters, as the hard metamorphic crystalline rocks of the Canadian shield are very resistant to erosion. In this case the Archaean plutonic rocks (magma that crystallises underground rather than erupting) melted on impact and they also reveal traditional impact indicators such as crystals of shocked quartz along with trace element enrichments suggesting that the impactor was a chondritic meteorite (which contain chondrules, mineral spheres preserving the environment of the early solar system when they crystallised). Another characteristic feature is present, called a negative Bougyer gravity anomaly. This occurs when the gravity seems low compared to the surrounding region, in this case due to the lower density shattered rock beneath the crater.

Loz

Image credit: NASA

http://www.nunavikparks.ca/en/parks/pingualuit/ http://earthobservatory.nasa.gov/IOTD/view.php?id=79743&src=eoa-iotd http://ottawa-rasc.ca/wiki/index.php?title=Odale-Articles-Pingualuit

Lightning Fires in the Arctic

The Northwest Territories of Canada had a record number of wildfires caused by lightning in 2014. Alaska did as well in 2015. A new study has found that the number of lightning-ignited fires in those areas has increased 2 to 5% per year since 1975, and linked the increase to climate change.

The researchers found that thunderstorms, and the fires they start, have been creeping further north as the climate warms. Warmer temperatures can fuel more thunderstorms, meaning the situation is likely to keep getting worse.

The areas being burned are along the margins where the boreal forest becomes the Arctic tundra. One of the dominant features of the tundra are the gelisol soils – soils which contain permafrost within 2 meters of the soil surface. Gelisols trap large amounts of carbon within the permafrost layers; the fires threaten to release that carbon back into the atmosphere, which in turn could lead to more global warming, which means even more thunderstorms and lightning-induced fires. This is known as a positive feedback loop.

If the fire doesn’t release all the carbon, it could still allow seeds from the boreal forest to plant themselves in the newly exposed minerals in the burnt soil, allowing the forest to creep north and thereby damaging the tundra ecosystem. In short, the northern ecosystem may be drastically altered very quickly.

Photo Credit: Government of Alberta, Canada https://go.nasa.gov/2uG3vjw

References: https://go.nasa.gov/2ubwiM2 http://bit.ly/2tE8Ure

Weird methane bubbles under the Siberian Tundra

Its not just large craters being caused by methane blowouts in the boreal regions of the globe (see http://bit.ly/29Qtoq7 for photos of the large craters that have appeared in Siberia), as revealed by this video recently published by the Siberian Times. A tract of grass and soil is underlain by a bubble of gas, making it float above the frozen matter beneath and bounce around like a trampoline. The research team found 15 such blisters in their survey of Belyy Island sits in the Arctic Ocean’s Kara Sea, a long running site for research into the changing climate up north (see http://bit.ly/2a62ppE for a summary).

As the world warms and the Arctic does so faster than any other region of the globe, to quote a geologist 'you turn the fridge off up north and everything starts to rot'. Indeed it seems that the permafrost (a mixture of frozen water, earth and organic matter) is doing just that across Siberia, northern Canada and Alaska, releasing methane (a greenhouse gas much more potent than CO2) into the atmosphere. Climate researchers call this a positive feedback loop, warming begets release of greenhouse gas which begets further warming some years down the line.

Loz

Image credit: Alexander Sokolov and Dorothee Ehrich /Siberian Times

Craters in Siberia, includes video: http://slate.me/1CBcFwh http://bit.ly/2aivxce

The Mayn River

A river’s features are best observed from afar, as this image of the Mayn River, which was taken by the Landsat 7 satellite, fully shows. Only from satellite images taken from far above can the meandering trait of rivers be fully appreciated. The squiggly, S-shaped character of meandering rivers is mainly due to the stream of water looking for the flow path of least resistance. A continuous balance between erosion and sediment deposition increases the S-shaped character of meandering rivers, creating landscape features that are the inspiration of many a geologist.

Located in northeastern corner of Siberia, the Mayn is actually tributary stream that flows from its source in the Koryak Mountains and through the forest-tundra regions of the Chukchi Peninsula into the larger Anadyr River. The Anadyr itself flows eastwards out into the Bering Sea. The frosty climate means that the streams in this region are frozen up to nine months of the year. During the summer seasons, however, the Mayn is a veritable source of chum and sockeye salmon for local settlements. Archaeologists have also found Neolithic-age artifacts such as stone-carved knives and pottery that probably indicates an ancient community that had molded its niche around the salmon-rich Mayn River.

-DC

Photo credit: http://1.usa.gov/1Cpwd3c

Further reading about the Mayn River and Chukchi Peninsula: http://bit.ly/1Cpwnra

http://bit.ly/1auYcZE

More about river formation and the math that you may not think was involved: http://www.dataisnature.com/?p=527

http://bit.ly/1ll0ltD

http://bit.ly/1auZ1BX

http://bit.ly/1J5lZuC

Ancient meandering streams on Mars?: http://bit.ly/1DJPYIt

World Biomes

Biogeography is the scientific study of the way plants and animals are distributed across the globe. Because climate and soil determine which plants thrive in a particular region, similar types of vegetation, as well as the animals associated with them, occur in places with climates that are similar. These places, occupying large areas and identified by their vegetation types, are known as biomes. For example, the belt of mainly evergreen coniferous forests that runs across Canada and northern Eurasia constitutes a biome known as boreal forest in North America and taiga in Russia. The character of this forest is essentially the same throughout the biome, but the plant and animals species found there vary.

There are twelve biomes in the world. Although general vegetation types can identify biomes, the vegetation in any biome is in fact quite varied because of a number of local differences in land use and environment. Tropical biomes occur between the tropics of Cancer (north) and Capricorn (south). Temperate biomes can be found in temperate regions, and polar biomes are located near the poles. Other biomes are more difficult to define precisely, because not all plant communities have clear boundaries. The range of plants in each biome makes it possible to draw the boundaries in different ways.

Around the poles, the polar ice biome supports no plant life. The climate is exceedingly harsh and there is neither soil nor liquid water at the surface. Bordering the polar ice is the tundra biome, where the ground is exposed and the temperature rises above freezing for a short time in summer. Along its edges, tundra gives way to boreal forest or taiga. Tundra and boreal forest are mainly confined to the Northern Hemisphere, because there is little land at the correct latitude in the Southern Hemisphere. Closer to the equator, deciduous trees become more common among the conifers of the boreal forest. The biome changes and temperate deciduous forest becomes more widespread. This biome is restricted to the continental regions with moist climates, while temperate rain forest is found only in the wettest regions.

As climates grow hotter and drier, the biome changes again. Temperate grassland, the prairies, steppes, pampas and veld, replace the temperature deciduous forest. In a few parts of the world there is a biome typical of Mediterranean climates, dominated by dry woodlands and chaparral shrub lands. A belt of subtropical deserts lies across both hemispheres. Deserts vary according to their locations, with some found along western coasts and some in the interiors of continents. Where climates are a little moister, subtropical deserts merge into savanna grassland. On either side of the equator there are tropical dry forests and rain forests. Mountain grasslands and shrub land biomes are not confined to particular latitudes.

The importance of biomes cannot be overestimated. Biomes have changed and moved many times during the history of life on Earth. More recently, human activities have drastically altered these communities. Thus, conservation and preservation of biomes should be a major concern to all.

~JM

Photo Credit: http://askabiologist.asu.edu/explore/biomes

More info:

World Biomes.com: http://www.worldbiomes.com/ World Biomes Map – Colouring in: Awesome activity for kids. http://www.classroomsecrets.co.uk/world-biomes-map/ Blue Planet Biomes: http://www.blueplanetbiomes.org/world_biomes.htm Terrestrial Biomes: http://www.nature.com/scitable/knowledge/library/terrestrial-biomes-13236757

Wonder lake One of the wonders of Denali National Park in Alaska it this beautiful body of water, seen here with mount Denali (6,168m) in the background. The landscape here is a combination of permafrost and tundra, deciduous Taiga forests and tall glaciated granitic mountains. The range of peaks is rising due to the subduction collision between the Pacific and North American plates that is responsible for the huge spine of the Americas, running south all the way from Alaska to Tierra Del Fuego in faraway Argentina and Chile. The park contains fragments of several of the micro terranes that have accreted on north America's west coast over the last hundred million years or so. Many have been metamorphosed, melted into granites and extensively folded and faulted by the immenso tremendous forces of continental collision. In fact this process provides a slow motion rough and ready answer to the old quandary of what happens when an irresitable force meets an immovable object.  Most of the terranes were oceanic sediments that were too buoyant to subduct, and their rocks were originally deposited in a variety of eras. The oldest is the Yukon-Tanana (1 billoin-400 million years old), now extensively transformed by its geological journey into medium grade metamorphic rocks. Next in line is the Farewell, a fossil rich sedimentary slice from the early half of complex life's evolution, dating from the Cambrian to the end Permian. The youngest terranes date from the Mesozoic era and consist of mixed sedimentary and igneous rocks, including pillow basalts first erupted under a sea full of ammonites and swimming reptiles. there is also an ophiolite sequence, where a chunk of oceanic crust has been pushed onto the continent , giving us a lovely insight into the marine crust/ shallow mantle interface. The youngest rocks comrpise something known as a flysh sequence, built up in the marine basin below the mountains where the plate was flexing down under the force of the grating subducting plates around a hundred million years back. The mountains are still growing and the many earthquakes in the area testify to the powerful forces stirring below. The recent ice ages sculpted all these rocks into the landscape we see today. Wonder lake itself is a glacial landform called a kettle, formed during the rapid retreat of the sheets when large chunks of ice melt more slowly than the rest because they are shielded by a protective layer of till (glacier shlep, rock dirt and flour). The overlying debris then settled and slumped forming the depression that has since been filled by rainwater and snow melt, though some of it was also directly carved out by glaciers. It is 6.5km long and up to 85 metres deep.  Loz Image credit: Rodney Lough Jr/ Nature's Best Photography http://www.nps.gov/dena/planyourvisit/campground-wonder.htm

Aurora Expeditions' Antarctica photo Contest. The image below is of leaning pillars of ice in Antarctica, one of 13 images taking either 1st place or runner up (from a number of categories, including landscape and wildlife photography) out of 284 judged in this years Aurora Expeditions Photo Contest. The overall winner of the competition was Andrew Lan, with his shot of a seagull flying over the Antarctic Tundra, and the image can be viewed here; http://www.australiangeographic.com.au/assets/images/article/journal/12359/aurora_antarctic_13.jpg Judge Mark Jones believes this shot captures the essence of Antarctica; the entries were also judged on photographic skill.  The image below was the runner up in the "Best Landscapes" category, and is my favourite shot from the bunch.  To see the rest of the images head to the link below. -LL http://www.australiangeographic.com.au/journal/aurora-antarctica.htm Image credit; Glendon Wesley