The Earth Story

Lights, Camera, Action!

As a geologist I spend a vast amount of time staring at rocks, whether it be out in the field or in the lab. Whatever I'm doing I always take pictures, as proof of what I've seen, evidence to back up my assumptions or just because a professor has demanded diagrams and I am artistically limited.

Through my education I have come to realise one thing; no matter how good the rocks look the key is lighting. When mapping in the Spanish Pyrenees the best light was at dusk or dawn, when the sun sat lowest in the sky. As you can see it beautifully highlights the cross laminations (bottom photo: laminations produced by the flow of material; the height of each set can indicate water depth and the direction in which the lines dip is the direction of flow) and slickensides (top photo: precipitation of minerals, here calcite, along a fault plane as one piece of rock slides past another) on the Buntsandstein Formation. These rocks represent an ancient braided river that swept eroded material off the Hercynian mountain range 250 million years ago.

As every good scientist knows there should always be a scale as the processes that form these structures are fractalic (they can form on a variety of scales through similar processes and it is their scale as well as their shape that define what caused the structures to form e.g. a rain drop and a river will produce similar structures during flow, the only difference being the scale of the structure formed). In this case I have used my GPS and my finger (it was very early in the morning and I had forgotten my ruler) to define the scale.

Image Credit: Watson

Further reading: http://bit.ly/1wMc04G

Divergent evolution

If you’ve gotten through a biology class you have probably seen an example of evolution triggered by the appearance of a mountain range. A species that has a population across a large area is separated by a growing mountain range, after which time it diverges into distinct populations. This transparent fish is a juvenile Galaxiid found in the streams of New Zealand, and its very existence is owed to exactly that type of speciation.

The Southern Alps on South Island are a rapidly developing mountain range that is still growing today. A few million years ago during the Pliocene, the geologic epoch that ended 2.6 million years ago, New Zealand had been above the waves for about 20 million years and freshwater fish had colonized its streams, but the Southern Alps hadn’t reached their current heights.

Today there are several dozen species of Galaxiids in New Zealand streams, but genetic evidence shows that during the Pliocene there were far fewer. The populations of fish exchanged across South Island, showing that the Southern Alps had yet to be such a strong boundary. Much of the divergence in these fish happened starting about the end of the Pliocene.

Just published research shows that other species, including insects, began to diverge into northern and southern populations shortly thereafter, during the Pleistocene. This divergence is thought to relate to the onset of glaciation on the island as there are occasional genetic exchanges between populations measured in those species.

These organisms therefore help date the uplift of the Southern Alps into a topographic divide. 5 million years ago these fish could exchange from stream to stream, but by 2.5 million years ago the processes of plate tectonics separated them into smaller populations.

-JBB

Image credit: http://bit.ly/2uZWehd

References and original paper: http://geology.geoscienceworld.org/content/45/7/595 http://bit.ly/2uYhPai http://www.ucmp.berkeley.edu/tertiary/pliocene.php

Andean rainshadow

Snapped looking northwards from the space station window somewhere over Chile, this stunning photo reveals why the strip between mountains and Pacific Ocean is mostly harsh and arid desert. In a usual year at these latitudes the trade winds blow over the South American continent from the Atlantic, bearing the moisture evaporated from the sea. As you can see, most of the resulting snow has fallen on the Argentinean side of the watershed, and most of the cloud lurks there too. When the oceanic air hits the mountains, it rises, and sheds its moisture as rain and snow before passing over and flowing onwards towards the Pacific.

On the western side of the chain most of the moisture has gone, and such rain as there is falls intermittently. Parts of the Atacama have not seen any recorded rainfall since the Spanish first arrived there. The clouds above the Pacific form well offshore, because a cold current of deep oceanic water is rising where the Pacific meets South America. These waters are cold enough to form fogs, but do not produce much in the way of rain bearing clouds. The barren eroding badlands that compose much of northern Chile are evident by their drab brown colours.

In an El Nino year like this one (see linked posts below) the trade winds stop and the cold current is inhibited, allowing rain to reach the coast, which often causes flash flooding. Argentina has a drier year and my home city of Montevideo is much less windy (though the trades are slowly picking up after a long absence, today they howl and dash rain against my window and I guess I'll just have to get used to their familiar presence again).

The EL Nino at work series: http://bit.ly/29YS6ps http://bit.ly/29EsXw6http://bit.ly/207KZt0, http://on.fb.me/1P1BV2O,http://on.fb.me/1OSg0dH, http://on.fb.me/1JEC5La, http://on.fb.me/1SjYm8e http://on.fb.me/1PuX6OQ, http://on.fb.me/1NUmrwU http://on.fb.me/1RT7l0M, http://on.fb.me/1mtXgKv, http://bit.ly/1SBlTkP

Loz

Image credit: Tim Peake

Spectacular views of the Alps, Switzerland, France, and Italy. Check out the how the sun moves on the slopes and how the clouds dance.

Pretty darn impressive plane view.

The mountain silhouetted in the foreground and the mountain reflected in the rearview mirror is just an awesome effect.

Dominating The Sky This beautiful photo, taken from the ISS, shows us the Himalayas looking south from over the Tibetan Plateau. “The Roof of the World”, as it is known, stands over 5000 m in elevation and is home to some of the highest peaks on Earth. It all started nearly 100 million years ago, when the supercontinent Gondwanaland broke up and India separated from Africa. The Indian plate traveled north at speeds faster than any plate moving today. After 50 million years it collided with Eurasia, completely closing the ancient Tethys Ocean. Rather than subducting, the light, continental rocks piled up, creating massive mountain ranges. The Indian plate has pushed more than 2000 km into Asia, and is still moving north. Today, the thickest continental crust on Earth can be found under the Tibetan Plateau, where it can reach 100 km in some places. Even though it is among the youngest mountain ranges on Earth, it has become the largest and highest area in the world today, and maybe even in all of geologic history. ~ SW More info: http://www.livescience.com/32531-how-did-the-tibetan-plateau-form.html

http://www.britannica.com/EBchecked/topic/266037/Himalayas/47869/Geologic-history

http://www.colorado.edu/geolsci/faculty/molnarpdf/1986AmerSci.Geology-Himalaya.pdf

Photo Credit: NASA

Orogeny We often talk about orogenies and orogenic events here at The Earth Story, but what is an orogeny? An orogeny describes a series of forces and events leading to the severe structural deformation of the Earth's crust and uppermost mantle (also known as the lithosphere). So in simple terms, an orogeny is a mountain building event. Occurring at the boundary where continental plates meet (th ough they can occur where a continental plate overrides an oceanic plate), the response to orogenic forces is basically a "crumpling" of the rock, leading to highly deformed and metamorphosed areas of rock, which extend far underneath the resulting mountain belt, and far beyond the front. The basic tectonics behind an orogeny is a subduction zone causing two continental plates to collide (or as discussed above it can occur at the meeting between an oceanic and a continental plate). The event can cause a number of tectonic features, including: volcanoes, mountain building, island arcs, back arc basins and of course earthquakes. A spectacular example of an orogeny is process is the Himalayas. This orogeny has been caused by the Indian plate and the Euro-Asian Plate, but all mountain belts have at some stage been part of an active orogeny. Once an orogenic event has completed the mountain building stage, the tectonics don't just stop! The mountain chain normally continues to uplift, and at the same time eroded; over millions of years this leads to spectacular views of metamorphic rocks and tectonics. -LL Links to some fantastic descriptions of orogenies and specific orogenic events: http://serc.carleton.edu/NAGTWorkshops/structure/visualizations/orogeny.html http://web.usal.es/~jrmc/MartinezCatalan/documents/AbatiEPSL99.pdf http://www.utdallas.edu/~rjstern/pdfs/PanAfricanOrogeny.pdf http://digital.library.adelaide.edu.au/dspace/bitstream/2440/23647/1/hdl_23647.pdf Image: Carsten Nebel

Location Location Location: Mountains, Climate and Vegetation  Earth’s land is a dynamic and ever changing landscape; folding, fracturing, and deforming the rock in many ways. Mountain ranges are thrust high into the air; sections of the ground sink, and volcanoes form conical mountains or inundate wide areas with lava.  Mountains in turn affect climate. With increasing altitude, soil and air temperatures tend to decrease, humidity becomes higher and the wind stronger. Mountains can also affect the amount of sunlight that an area receives. In the southern hemisphere the north-facing slopes are exposed to more sunlight than the south-facing slope. Slope also affects wind speed, determining how sheltered a place is. The steepness of a slope also affects the amount of surface runoff and the water content of the soil.  These climatic changes are reflected in the vegetation, which can vary from tropical rain forest at the base, through grassland and tundra, with arctic conditions near the summit. The vegetation of an equatorial mountain varies with climatic changes at different elevations, or ‘zones’. Even in tropics high mountains are capped with snow and ice. Here is an example of a mountain environment and its different elevations. Mount Kenya is an extinct volcano and is Africa’s second highest mountain. It has dry forests around the base, gradually changing to bamboo, with alpine meadow above the timberline. 2,000 Meters (6,500 Feet) Savanna – Plants can be found in this zone including trees, grass, and ferns. The land is also rich for agriculture. Montane forest – This zone supports trees and shrubs, mosses, lichens and ferns. 3,000 Meters (10,000 Feet) Bamboo belt – Bamboos are the tallest grasses and form dense thickets. Along the lower margin of this belt there can be wildly scattered juniper trees. 4,000 Meters (13,000 Feet) Sub-alpine moorland – This region has a milder climate and supports taller herbs and shrubs and African rosewood trees. 5,000 Meters (16,000 Feet) Afro-Alpine – Herbaceous plants grow in this zone. Some, such as giant lobelia and senecio, grow to the size of small trees. 5,000 + Meters Summit – Too cold and windswept for plants to survive, this consists of bare rock with no soil and is capped with ice and snow year-round. These principles apply to all mountains but can vary significantly from mountain to mountain. If you have any cool pics of any places you have visited that demonstrate this and you would like to share them for others to see, then please do so in the comments.  ~JM Image Credit: http://en.wikipedia.org/wiki/Mount_Kenya Further Reading: Mount Kenya National Park http://whc.unesco.org/en/list/800 African Natural Heritage http://www.africannaturalheritage.org/mount-kenya/ Mountain Ecosystem http://www.britannica.com/EBchecked/topic/394887/mountain-ecosystem/70823/Environment Impact on mountain vegetation zones http://www.grida.no/publications/vg/climate/page/3081.aspx Linacre, E., & Geerts, B., (1997). Climates and Weather Explained. New York. London. Routledge.