Sand Dunes - Intro to Geomorphology

Geomorphology is the study of land-forms: how did the land get those shapes, what are the processes behind them, and how can we use that information in a practical way? 

For instance, why are the Appalachians really rather low hills compared to the Rocky Mountains? We understand from geologic mapping that the Appalachians were once as high as the Rockies, if not taller. However, they have been under a weathering regime (water and wind erosion) for far longer. The active building phase in the Appalachians stopped about 300 million years ago in the early Permian era – and they have been eroding ever since. The Rocky Mountains, on the other hand, were uplifted between 100 and 65 million years ago. In this case, the rounded shapes simply mean that the Appalachians are much older. There are sedimentary units in Venezuela that are dated about 1.7 billion years old that are weathered remains of even more ancient mountains that no longer exist – they have been weathered flat.

A good example of geomorphology and what it can teach us is exemplified by the following question and answer sequence, sent to the USGS Ask-a-Geologist website. In deserts worldwide there are different kinds of sand dunes, with many different and distinctive shapes. The Empty Quarter of the Arabian Peninsula is loaded with many of the most classic dune-types: Saif (sharp-edged “sword”) dunes, ‘Irq (200-kilometer-long “vein”) dunes, Barchan (huge horn-edged, crescent-shaped) dunes. There are also more complex products like Star and Zibar dunes, typically bridging one dune-type region and another. There are also lag-gravel plains – flat areas covered by small pebbles that keep the diurnal wind-storms from moving the sand beneath them.

Careful examination of sand textures (fine, clay-like particles vs beige quartz sand, for instance), and dune shapes leads to an understanding of the annual wind regimes in these areas. On any given day, there is a diurnal sand storm: at dawn the wind is dead still, but around 10am it starts to pick up. By 5pm, when we would be trying to set up our tents, the wind would be shrieking along at 30-40 knots, blowing stinging sand at eye-level. Every hour we would wake up during the night, because the humidity was ~2% and our throats would be on fire. The first thing we did was brush the dust and sand from our eyes, THEN open them, THEN take a drink from our coolers. The wind would die down to nothing sometime after midnight, and we would find trails of scorpions and dung-beetles (and camel spiders trying to find a way into our tents) that were brand-new and fresh from just the previous hours of the night. 

There are also seasonal changes, and can be more important than you might think. Dunes in the northern Empty Quarter show that there is an annual 10-month wind-pattern that reverses direction and ramps up in speed and intensity in February and March every year. These changes correlate with the Monsoon season in the nearby Arabian Sea. This 2-month-long sand-storm period (the “Khamsin Season”) would have shut down 1990’s Desert Storm war in its tracks. This forced US military planners to rush the start of the fight to reclaim Kuwait from its Iraqi invaders in January, 1991. 

These sandstorms can be truly terrible things, shutting down all human movement for days at a time, stinging your face and literally suffocating unprotected humans foolish enough to try to walk about in it.  I once flew in a Boeing 737 jet on a scheduled flight from Jeddah, Saudi Arabia to ‘Ar-‘Ar in the north near the Iraqi border. The pilot circled the town three times, but we couldn’t SEE the town: ‘Ar-‘Ar was completely obscured by flying sand and dust. The pilot abandoned his attempt to land and we flew instead 500 kilometers farther west to Tobuk, where we were forced to re-plan our entire phosphate resource exploration and mapping effort. A few years later I flew on the single remaining commercial aircraft then owned by Air Mauritania… and learned that the only other Fokker aircraft had crashed just two weeks earlier while trying to land in a sand storm that severely damaged its jet engines. I noted as we landed at Nouakchott (the capitol of Mauritania; the name comes from the Berber language for “place of the winds”) that a sand-storm was already raging. The flight had people standing in the aisles the entire time – it was severely overloaded – and the pilot indicated that he was running out of fuel.

These monster sand storms are not all bad. We finally made it to ‘Ar-‘Ar, but the dust hung in the air for many days. It allowed me to look directly at the setting Sun without eye-protection as we carried out our geophysical well-logging efforts. At that time (1994) there was a huge sunspot cluster that migrated from the upper left quadrant to the lower right quadrant of the afternoon Sun - I sketched it as it evolved over four days in my field notebook. Without using any astronomical instruments, this meant that I could determine the spin axis of the Sun: it is oriented at about 45 degrees to your upper right as you look to the west. I could also roughly determine the Sun’s rate of revolution – about 10 days – using just the naked eye. This must have been possible centuries ago, but I’m unaware of any ancient scientists figuring this out.

Q:

Subject: sand dunes

I am displaying a photo below of sand dunes in Saudi Arabia, in the Empty Quarter near UAE (Arabian Peninsula). They are from Google Earth and were 'taken' from 8 km high. I have tried to read your publications on classification of sand dunes so I could identify these dunes, but alas, I failed!!!  

Can you tell me what kind of dunes these are and from which way was the wind blowing to generate them?  

Thanks

- Hale S

A:

You didn't fail, you're just looking at a transition zone there... in the mid-distance you have merging Barchan dunes (wind is blowing from the lower left of your image, and the “horns” of the Barchan point in the wind direction). In the near distance the Barchan dunes are transitioning to Saif (sword) dunes (the wind is coming from the left side of your image). I actually did a traverse across the Empty Quarter, not too far west of where this image comes from, on an expedition from Yemen to Dhahran to map the Wabar meteorite impact site.  There is an awesome USGS book called "Global Sand Seas" (Professional Paper 1052, Edwin D. McKee, Editor) that will give you quite a bit more information, including provenance (sand source areas) and wind-rose diagrams.

Q:

 Thanks for your reply -- now I'm going to think about your answer and try to digest it - on top of a Thanksgiving dinner! That is a LOT!!! 

I thought I recognized your name -- you and Gene Shoemaker investigated the (Wabar) crater and you wrote the paper after Gene died (“The Day the Sands Caught Fire”, by Jeff Wynn and Gene Shoemaker, Scientific American, November 1988 issue). I have read it and enjoyed it. Good job! I would give an arm and a leg -- well, maybe a fingernail -- to spend time in the Empty Quarter, photographing and looking at the area. As you might tell, I am a desert nut!

I found the paper by McKee et al on the Net and have started reading at it...  It is a long one!!Many thanks

 Hale 

A:

The McKee book is great - typical quality for a USGS Professional Paper - Enjoy!  Yes, I would stop everything to jump in on another Empty Quarter expedition.  The Zahid people, the corporation that engineered (literally and figuratively) the three Empty Quarter expeditions I participated in, told me privately that the cost added up to about $10,000+ per seat for each expedition. The Empty Quarter is a truly amazing place; humidity routinely drops to ~2% there. I once completed a magnetic profile survey at Wabar when the temperature at mid-day reached 61 degrees Centigrade (142 F). I am a "desert junkie" myself, now living in the soggy Pacific Northwest.  I also maintain a website about the relatively rare Empty Quarter expeditions: http://www.empty-quarter-expeditions.org

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History Channel's Bamazon spews POISON

I mean that literally.

The History Channel, which used to host educational content, has apparently chosen to do something quite different. In my opinion, they are glorifying environmental destruction. For another opinion, check out ellemadame.blogspot.com for the opinion of someone who has been there. Here she is, visiting one of the ecologically-destroyed sites in the Las Cristinas area of Bolivar State in Venezuela:

For reference, that was once a deep forest, full of biodiversity and just plain beautiful. Not anymore.

I started out my professional life as a mining geophysicist. I had just earned my PhD, and with my dissertation advisor had started a company to provide electrical geophysical services to mining companies in the US and Canada. This meant that I used geophysical methods to search for undiscovered mineral resources - mainly porphyry copper deposits in the southwestern US, Alaska, and western Canada. When successful, this geophysical exploration led to large-scale mining done in a very controlled fashion so as not to damage the water table or the local environment.

Are you reading this by using a light? You can thank a copper mine that you have wires in your house. Or that your car works.

Also - and this is more important than you may possibly imagine - thank the US Bureau of Mines (now defunct) and the Environmental Protection Agency for insisting that the water you drink does not have cyanide or mercury in it.

I subsequently joined the US Geological Survey, and several years later accepted an assignment from the US Geological Survey to provide technology transfer to Venezuela - and with my wife we wrote a book about this. I was the chief of the USGS science technology mission to Venezuela - paid for 130% by the Venezuelan government (the extra 30% went to overhead so that US taxpayers actually got some payback).

When we arrived in Venezuela with our family, the southern half of the country was literally unmapped - only 1:250,000-scale SLAR (side-looking airborne radar) images existed for the jungle-covered southern half of Venezuela. Those maps were so bad that you could see "splice errors" - where two radar strips laid out together would mis-match a point on their edges by 3 kilometers. In the three years we were there we mapped the Amazonas, and completed a mineral resource assessment of the country (see also http://pubs.er.usgs.gov/publication/b2124) that showed it to be incredibly endowed with mineral resources, including gold, diamonds, rare-earth elements ("REE's"), iron, and bauxite.

As I continued showing and training the Venezuelans how to use geophysical and geochemical methods, and built a  full mineral resource estimate for the southern half of the entire country, I began to see an unanticipated consequence of our good intentions. I had not anticipated that something like the EPA would not exist in Venezuela. I had also not anticipated the consequences of massive political corruption on a country and its economy.

So-called "artisanal miners" were being driven into the jungle by the collapsing economy of Venezuela. Why was the economy collapsing? Two political parties, deliberately designed to look like the Democrat and the Republican parties in the United States, had taken turns for over 30 years to loot the country of far more than it was producing in oil wealth. Political corruption got so out of control at the time that it was literally bleeding the country white. Wealthy women in Caracas thought nothing of flying to Miami for the day to go shopping. They loved the fact that everyone spoke Spanish with Cuban accents, "...and Miami is so CLOSE to America!" But the average people not in on the corruption circle lost their jobs in droves - the economy was collapsing at a rate of several percent per year, driving poor people desperate for food into the jungle to do whatever they could to survive. After all - that's where their grandparents came from, and they panned for gold and fed their families.

That was before hydraulic pump technology became available.

This is ALL described in The Book - which helps the average American understand why the Venezuelan people had become so desperate that they elected Hugo Chavez as president of Venezuela. They had SEEN what the pious, American- and European-educated elite had called "democracy" - and wanted no more of it. Paternal socialism - where the poor people discarded to the hillside slums actually were helped to live and to eat - was a huge improvement by comparison. For the first time, someone cared about the people who were not rich and educated in America. Chavez grew up the son of poor school teachers - in a dirt-floored hut in Western Venezuela.

The result of the consequent artisanal mining - glorified in the "History" Channel series Bamazon, has been the destruction of the great Amazonas forest on a truly colossal scale.

And it happens incredibly rapidly.

One day I was walking a jungle trail and was amazed to see a brightly-colored, brand-new hydraulic pump sitting by itself in the middle of the trail. This thing weighed at least 200 kilos - more than 600 lbs - and I wondered how it got there. The next day I returned with my Venezuelan counterpart to show him. Where the pump had been we now gaped at a water-filled hole in the ground. This hole was about 2-3 meters (6-10 feet) deep and at least 20 meters (65 feet) in diameter. The hydraulic pump was nowhere to be seen - we learned later that six mineros slung it on ropes from a pole and moved it by cutting a new trail through the jungle to a new site.

The hydraulic pump had been used to water-blast the soil out from under the ancient 50-meter (160-foot-tall) trees that had stood there just a day earlier. They were now fallen over - and dying - around the perimeter of what the Venezuelans call "agua negra" - black water. This water was still and black - and because it was not moving naturally through a drainage, it would now host malaria-carrying mosquitoes for the next several centuries.

Anecdote: falciparum plasmodium, the so-called "cerebral malaria", can leave you in a coma in as little as two hours after the onset of the first massive headache. It kills. It is also resistant to all prophylactic drugs available in Venezuela.  

The Venezuelan government no longer reports two kinds of national statistics:

• the number of malaria deaths in the country
• the murder rate in the country  (el Nacional, a privately-owned newspaper, reports that it is over 10 times the murder rate in Baghdad).

In two visits to the mining village at Piston de Uroy, in southern Bolivar State on the Rio Chicanan, we met some of these miners. Typically they wore nylon shorts and flip-flops. Their village, as the roughly-hewn beer-and-mercury-selling bodega (store) owner told me, hosted 600 miners and "300 putas" (prostitutes). When we visited the village only 6 months later, there were just 300 hardy residents left there alive. All the rest, the bodega-owner told me, had either died or gone down the river to the government malaria clinic in El Dorado. They had already left behind a centuries-long ecological disaster (below).

I mentioned that the bodega-owner also sold mercury. This is called "asogue" in Venezuela, and is used to amalgamate with the dust-grain-sized gold into "sponge" - which the miners typically cook on stoves in their shanties. They literally cook it in sauce pans to get the mercury to boil off and leave the gold. Guess where the mercury goes? Yep - they breathe it. You might want to check out Minamata Syndrome.

Shortly after we arrived in Puerto Ordaz, Venezuela, for our three-year assignment, a Venezuelan friend, a geochemist with a Doctorate of Science from the Colorado School of Mines, dropped a report on my desk. "Read this and get it back to me by tomorrow," he said. "If anyone learns that I gave this to you, I will lose my job," he added. The report documented the fact that the Caroni River, where our town drew its water supply, already was showing methyl mercury levels 7 times greater than the maximum permitted by the EPA in the United States. River fish had up to 1,200 times the maximum FDA limits in their flesh. The report said that secret government estimates, based on import data, suggested that 70,000 liters of mercury were dumped into the Rio Caroni drainage every year. A liter of mercury weighs about 33 kilos (~70 lbs).

We drank no more tap water for the rest of the three years we lived there. We also avoided eating river fish.

Here's an example of how hydraulic mining is done:

Note the guy on the left with the hose - that's what is used to undercut the soil and knock over the great trees. The guy in the lower center is standing in a hole with his feet guiding the suction-pump stream to a bolus of mercury. The pump in the upper right takes the mercury and gold results and runs it over a "grizzley", or shaker-table, where the heavy components drop out and get trapped in wooden riffles. This is later gathered and "cooked".

Here's what the results look like from a distance; note that the amount of damage seen here from my helicopter can be caused in just a week's time:

The scale in this image is approximately a kilometer (0.61 miles) on a side.

So... what is gained by this kind of hydraulic mining in the jungle? Gold. How does gold feed the human population? It doesn't - except like cocaine, rich people spend money on it and a tiny fraction of that filters back to the artisanal miners. Unlike platinum, it can't even be used in catalytic converters. It's used to coat some electronic components, but also used to flag to everyone that you are married. And to quickly squirrel drug money in a compact form out of a country.

The Take Away here: 

• Don't watch the "History" Channel's Bamazon series. 

• Don't buy anything from a company that advertised there.

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