The Earth Story

Alluvial Fan

Some of the best examples of alluvial fans on Earth can be found in Death Valley. Alluvial fans like this one form in dry environments with high topography that leads to high sediment supplies.

Sediment erodes from the high hills nearby and on the rare occasion when it rains, it is washed into thin canyons, often in flash floods. Those canyons carry the sediment down the channel until they open into the wider valley. At that point, the waters slow down and spread out, dropping the sediment into a pile. The sediment flows out in all directions from that point, creating a fan-shape that peaks at the top and spreads out.

One other interesting Death Valley phenomenon shows up here as well. Notice how there are no boulders anywhere outside of the fan? The bottom of Death Valley is a dry lakebed that has concentrated salts eroded from the area. When any large chunk of rock gets out past the edge of the fan, it is rapidly coated with salt. That salt wedges its way into the rock every time it gets wet and rapidly destroys the rock. The salt splits apart the rock at grain boundaries, taking boulders and literally turning them to dust.

If you’re ever out in these salt flats, seriously look at the sediment around. It goes from rocky on the fans to almost completely powdered and held together by salt out in the flat.

-JBB

Image credit: Alisha Vargas https://www.flickr.com/photos/alishav/3261819099

Read more: http://books.google.com/books?id=EvfgqYRyCUAC&lpg=PA79&ots=CUB3RS4Vju&dq=Death+valley+salt+weathering&pg=PA82#v=onepage&q=Death%20valley%20salt%20weathering&f=false

Simple but awesome views of some of the Rocky mountains, Moraine Lake, and Lake Louise, Banff National Park

A series of wingsuit base jump clips from New Zealand above glaciers, mountains, rivers, snow, and even the clouds.

I wonder if it’s possible to get anyone who spots something geologically interesting to add a comment. I’ll even start -watch for alluvial fans and bars in the river at the base of their valley.

Fanning out

When channels eroded into mountain ranges cross a boundary and expand onto open plains, the streams in them tend to spread out into wide features known as alluvial fans. This fan is found on the southern side of the Taklamakan Desert in China, where streams from the Tibetan Plateau spread out into the basin below. Flow happens only occasionally in streams like this, often taking the form of flash floods. When a major rain event happens upstream, the rain coming out of the channel picks a path towards the low ground and that path changes basically every time. The active flow heads to low ground, deposits sediment on its way that can block that channel or change the topography, and then the next time the fan becomes active the water finds a different route to the base. Thus, an alluvial fan builds up as a pile of sediment spreading out in all directions from the central point – where the channel enters the basin.

This image was taken by the ASTER instrument on NASA’s Terra Satellite – a multispectral imaging instrument capable of measuring light at a number of different wavelengths between the visible and the infrared. Different surfaces on Earth absorb light at different wavelengths, so measuring the amount of light reflecting off the surface at different wavelengths gives information about what is there. The blue color here has been tuned to a wavelength where vegetation is present – therefore, the blue light tracks a channel system where plants were able to grow. Plant growth, of course, requires water, so this image therefore shows which channels were active during the most recent rain event on this channel. That instrument has been flying for nearly 20 years, building up a database that can let scientists see how these features evolve over two decades.

-JBB

Image credit: NASA/GSFC https://flic.kr/p/7HeRA7

Instrument: https://asterweb.jpl.nasa.gov/instrument.asp

The Jewel of the Kalahari.

The Okevango Delta in Namibia and Botswana delta receives the rain from a large catchment area extending northwards into Angola's Plan Alto highlands at 1200 metres altitude. While it looks lush and green, it is in fact an oasis in the Kalahari desert, receiving water from a faraway and different climatic zone.

The depression the water spreads into is an endorheic rift basin (without an exit to the sea) at the southern end of the Great African rift system, which gradually absorbs the water when the rains from the annual wet season (Jan-Feb) reach it. About 11 cubic Km of water flows over 1200 Km to fill it every year, gently spreading over the next months to bring a wave of spreading green through the delta. The feature is also a giant alluvial fan, with permanent, seasonal and occasionally flooded areas such as Lake Ngami. The height variation is very small, less than two metres over its whole length, making the flooding a gradual affair.

The flood peaks during Botswana's dry season, making it a refuge for many kinds of wildlife in search of water in the parched Kalahari as it swells to three times its normal size. It is a biodiversity hotspot, with emblematic animals such as elephants and hippos gathering to enjoy the water. 150 species of mammals and over 500 of birds make it their home. Is annual growth and shrinkage makes for fantastic time lapse satellite footage. It provides a refuge for much of desertic southern Africa's wildlife when drought strikes.

It was declared one of the seven natural wonders of Africa last February in Arusha, Tanzania, and is on the tentative list for recognition as a UNESCO world heritage site.

Loz

Image credit: NASA

http://whc.unesco.org/en/tentativelists/5554/

Here’s a cool geology drive - the road to Badwater, lowest point in Death Valley National Park. The road moves away from the front of the range as it passes the Death Valley alluvial fans - when a stream enters the valley it spreads out and dumps a fan of sediment around that site. The road peels away from the mountain as it goes around these debris fans. This road also occasionally gets torn up by water during flash floods. 

Life Valley

Every few years, typically during El Niño events when rain is more common, wildflowers that scattered their seeds during the last rainy year poke their heads above the ground and create a widespread bloom in Death Valley. This panorama captures the beginnings of such a bloom this year. There is a nice alluvial fan in the foreground, now covered by a carpet of yellow and green.

-JBB

Image credit: Marc Cooper https://flic.kr/p/DpDtzA

More: http://nyti.ms/1oDXgtd

Atacama desert also in bloom: http://tmblr.co/Zyv2Js1xL19-r

Lake Manly

10,000 years ago at the end of the last glacial period, all of the valleys in Eastern California hosted lakes fed by meltwater in the mountain glaciers. That water eventually drains downhill to the lowest elevation, forming a lake at the bottom of Death Valley. That lake is named Lake Manly, after William Manly – a member of a group that survived traveling west from Salt Lake City across Death Valley in the mid-1800s.

El Nino years commonly bring rains to the deserts in eastern California. When those deserts get enough water, it begins migrating downhill to the lowest point under the influence of gravity, the same place that once hosted Lake Manly.

2015 has seen the formation of a record breaking El Nino event and it is already bringing some rain to the California Desert. This shot shows that 2015 has already seen one filling of Lake Manly, and there may be more to come. In some years, the water level rises enough that people will head out on the waters in kayaks and small boats.

The bottom of Death Valley is filled with a series of rugged, jagged pillars of sediment and salt. When Lake Manly is restored, the water first fills in the gaps between these features then possibly rises upwards from there. Those pillars of the Devil’s Golf Course create the rocky pattern in-between the pools of water.

In the distance, the first light of the sunrise is beginning to illuminate the peaks of the Panamint mountain range, with the clouds hiding the highest tip. Telescope Peak, the highest peak in the Panamints, rises to a height of over 3300 meters, towering over the below-sea-level basin below. The sun is just about to migrate down to illuminate one of Death Valley’s famous alluvial fans, formed as sediment from the mountains is carried into the valley by occasional flash floods.

-JBB

Image credit: James Marvin Phelps https://flic.kr/p/A3DaWt

Read more: http://www.lakemanly.org/ http://www.panamintcity.com/basin/lakemanly.html http://www.nps.gov/deva/planyourvisit/furnacecreekarea.htm

Patterns of organic energy

Mountains are energetic places, from the slow grinding tectonic rise to the powerful forces of erosion that they invoke by their presence and height. They attract rain and snow by forcing air to rise and its moisture to condense into clouds, and then either store it as glaciers or lakes or get carved out by the flowing water (liquid or solid) as it runs down following gravity towards the sea. Said carving results in a variety of features, such as deep gorges and U shaped glacial valleys, and, of course, in a vast amount of sediment that also journeys towards the sea (until the inevitable moment when the tectonic event ceases, and erosion wears them away to a flat and boring peneplain).

Much of the larger sediment moves in bursts when more powerful weather events move large amounts, while the background rate of downward flow is fairly gentle. Every year in the Himalaya for example, when the monsoon strikes, roads all over the region are washed away in landslides as the sediment saturates and falls downwards. An ice age is another large spurt at a longer timescale in a rock's journey from mountain to deep sea sediment. This means that a particle of sediment may well spend quiet aeons in storage in a sediment reservoir, awaiting the conditions powerful enough to remobilise it into a new phase of the journey.

The photo depicts a region near the India/China border, with one of the main ranges at the top. Sediment from the mountains, much of it probably from the last ice age, has been distributed into alluvial fans, the large flat areas just to the south of the chain. As the streams carrying it emerge from the steep mountain area onto the flatter fan, their energy decreases, and they form braided rivers and dump alot of their sediment, since they lack the energy gradient to carry it any further. Such melt water and rain as the summer provides has carved a lovely dendr itic (tree like) drainage pattern and a couple of deep gorges to complement the energetic pattern. .

Loz

Image credit: NASA

http://earthobservatory.nasa.gov/IOTD/view.php?id=85721&src=fb

Geology: Like Cluedo, but with less death and more rocks The job of a geologist is to study the rocks around them (their clues) and then come up with a hypothesis as to how they all ended up in their current state and condition.The photo below shows a megaclast (larger than a boulder >4.1m) of Cambrian Gonessa Limestone within younger Ordovician Mt Argentu Schist that was observed in southwest Sardinia. But how did a huge isolated clast of limestone end up standing proud within a large outcrop of schist? It is unlikely the clast was deposited by fluvial processes due to its anomalous size. Faulting was also disregarded due to the lack of field evidence (the contact is non-linear and not at a consistent orientation). After careful consideration of the tectonic history and depositional environments it was proposed that the megaclast represents an olistolith ( ‘a pebble to several kilometre sized clast foreign to the host rock in which it is emplaced’ Cieszkowki, et al., 2012) emplaced shortly after the Sardic Phase (Cambrian age collisional event) of deformation. A likely hypothesis is that this outcrop originated as a Limestone cliff overhanging an alluvial fan. Due to weathering, erosion and an increase in pore fluid pressure, a large section of the cliff cleaved off and fell into the muddy sediment below. This piece of cliff was originally emplaced horizontally within the sediment, however it is now standing vertical (stromatolite fossil evidence confirms this). So how did it go from horizontal to vertical? Well Sardinia has had a rough history, having undergone several orogenic (mountain building) events as well as its fair share of volcanism. During this time it is proposed that folding led to the clast being returned to vertical and that subsequent erosion of the more easily weathered schist left the clast standing tall (see my rather crude sketch below). However, as with most things in geology this conclusion is not set in stone (badum dum tss). The evidence we have so far indicates that the most likely emplacement of this clast was an olistolith but if new evidence comes to light this could easily change. - Watson Refrences:  Paper Citation - Cieszkowki, M., Golonka, J., Ślączka, A. & Waśkowska, A., 2012. Role of the olistostromes and olistoliths in tectonostratigraphic evolution of the Silesian Basin in the Outer West Carpathians. Tectonophysics, pp. 248-265. Further Reading: Paper Citation - Ślączka, A. et al., 2012. Sedimentary basins evolution and olistoliths formation: The case of Carpathian and Sicilian regions. Tectonophysics, pp. 306-319. http://www.sciencedirect.com/science/article/pii/0037073870900229 Image Credit: Watson Horrific Sketch Credit: Watson 

Alluvial Fan Some of the best examples of alluvial fans on Earth can be found in Death Valley. Alluvial fans like this one form in dry environments with high topography that leads to high sediment supplies.  Sediment erodes from the high hills nearby and on the rare occasion when it rains, it is washed into thin canyons, often in flash floods. Those canyons carry the sediment down the channel until they open into the wider valley. At that point, the waters slow down and spread out, dropping the sediment into a pile. The sediment flows out in all directions from that point, creating a fan-shape that peaks at the top and spreads out. One other interesting Death Valley phenomenon shows up here as well. Notice how there are no boulders anywhere outside of the fan? The bottom of Death Valley is a dry lakebed that has concentrated salts eroded from the area. When any large chunk of rock gets out past the edge of the fan, it is rapidly coated with salt. That salt wedges its way into the rock every time it gets wet and rapidly destroys the rock. The salt splits apart the rock at grain boundaries, taking boulders and literally turning them to dust. If you’re ever out in these salt flats, seriously look at the sediment around. It goes from rocky on the fans to almost completely powdered and held together by salt out in the flat. -JBB Image credit: Alisha Vargas https://www.flickr.com/photos/alishav/3261819099 Read more: http://books.google.com/books?id=EvfgqYRyCUAC&lpg=PA79&ots=CUB3RS4Vju&dq=Death+valley+salt+weathering&pg=PA82#v=onepage&q=Death%20valley%20salt%20weathering&f=false

Alluvial Fans. So what is an alluivial fan? Well, an alluvial fan is a fan-shaped sedimentary deposit that occurs when there is a significant decrease or break in gradient, usually at the edge of mountain chains. A group of alluvial fans that converge into one large fan shaped deposit is known as a Bajada. Alluvial fans are commonly found in desert areas, and areas that are prone to flash-floods. A great example of alluvial fans are found in Death Valley, USA. They can also be found in wetter, more humid areas, and there one great example is the Koshi river in Nepal. The river has built a "super-fan" covering 150000km2. Head to any of the links below to find out more. -LL Links: http://eps.mq.edu.au/courses/GEOS260/alluvialfans.htm http://pages.uoregon.edu/millerm/fan.html Image: alluvial fan in the taklimakan desert xinjiang province from May 2002. Source; http://www.geog.ucsb.edu/

International Dark Sky Week We covered earlier how this week is National Parks Week in the U.S., celebrating the national parks of that nation. Turns out, it’s another Earth-related week as well; this is International Dark Sky week, a week to remember what the skies used to look like above our heads. Light pollution does a lot of things…first, it spoils views like these, taken over one of the United States’ National Parks. In addition it has biological effects, altering the rhythms of day and night that animals and even humans use to calibrate their bodies. Artificial lights can interfere with the navigation of animals, leading animals like birds and young turtles off course when they are trying to migrate. This photo was taken while looking up from Badwater Basin in Death Valley National Park, where some of the darkest skies in the world can be found. In 2013, Death Valley was declared a Gold Tier International Dark Sky Park, only the third in the U.S. park system and the largest park with this designation in the world. Night sky isn’t something we normally think about among the many things preserved by National Parks, but a view like this of the Milky Way over one of the alluvial fans that dot the floor of Death Valley is just one of the many positive results of protecting these fragile areas. But even here, you might notice a tiny bit of excess light - a pair of car headlights on the road that winds its way past these alluvial vans. -JBB Image credit: Rene Jakobson (Creative Commons license) https://www.flickr.com/photos/renej/13078302304 Read more: http://darksky.org/int-l-dark-sky-week-main http://www.nps.gov/deva/naturescience/lightscape.htm http://www.livescience.com/27284-death-valley-largest-dark-sky-park.html