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(Earth) Deserts: Sand Dunes

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PostPosted: Tue May 09, 2006 5:44 am    Post subject: (Earth) Deserts: Sand Dunes Reply with quote

American Association for the Advancement of Science
4 May 2006

Sand on titan, saturn's largest moon

The planet Saturn has a moon named Titan, and on this moon, scientists have discovered long and tall rows of sand that look just like sand dunes in the Sahara desert, as well as other deserts in Africa, Australia and Arabia.

There are different kinds of sand dunes on Earth. The sand dunes on Titan look like the dunes that form on parts of the Earth where the wind blows in one direction then in another direction and then back to the first direction and then back to the second direction. If the wind blows in just the right back-and-forth pattern, sand builds up in long parallel lines.

Scientists discovered that the same thing happens on Titan, though the main reason why the wind changes direction on Earth and Titan is different.

"We can see mounds of sand on Titan that are exactly the same size and shape as sand dunes on Earth," said Science author Ralph Lorenz from the University of Arizona in Tucson, Arizona.

On Titan, all this wind blowing has created long rows of sand that look – from above -- like the shape a kitten might scratch into your arm if it plays too rough. The tallest rows of sand are nearly 500 feet high.

Images taken from a spacecraft named Cassini as it flew by Titan led the scientists to the discovery of Titan's familiar-looking sand dunes.

Now that we know there are sand dunes on Titan, we have new information about Titan's environment. For example, we know that there have been long periods of time without lots of liquid water on the surface of Titan. We know this because the liquid water would have acted like a sand trap and stopped the sand dunes from forming.

Sand castles on Titan? Not so fast. Aside from the fact that there are no people on Titan, the sand isn't exactly like sand on Earth. In fact, scientists are not sure what the sand is made of -- but there are two likely candidates: either ice made of frozen water or tiny clumps of carbon that are similar in their chemical structure to petroleum.

So if you are playing the "sandbox word game" with a friend, imagining a sandbox on Titan will be exciting…

I one the sandbox.
I two the sandbox
I three the sandbox.
I four the sandbox.
I five the sandbox.
I six the sandbox.
I seven the sandbox.

…because when you get to the most important line in the game:


you'll be "eating" tiny bits of ice or carbon!

This research appears in the 05 May 2006 issue of the journal Science.


Questions to explore further this topic:

What is sand?

What is a desert?

The Desert Ecosystem;edu=elem;edu=mid;edu=high

How does the atmosphere influence aridity?

Where do deserts form?

What are the different types of deserts?

What are the different features of a desert?

What is the Eolian Process?

Remote Sending of Arid Lands

Mineral Resources in a desert

What is desertification?

What are sand dunes?

Dune formation and reactivation

City-swallowing sand dunes

What are the different types of dunes?

What are coastal sand dunes?


The Great Sand Dunes of Colorado

An Introduction to the Geology of the Great Sand Dunes

Characterizing grains of sand

Magnetic Sand

Measuring sand density

Natural History of Sand Dunes

Cross section of the Great Sand Dunes (San Luis Valley, Colorado)

Wind Patterns and Sand Dunes

Where does the sand come from?

How much sand is in the Great Sand Dunes of Colorado?

Escape Dunes

How do sand grains move?

Hydrology of the Great Sand Dunes

Is there an ocean in Colorado?

Calculating water flow

Cohesive forces in sand

Sand Filters

Ecology in the Great Sand Dunes

Life Zones in the Great Sand Dunes

Endemic Insects

Photos of Sand Dunes

Animals and Sand Dunes

Plants and Sand Dunes

Out of the Blue: A Collection of Student Activities

La Paz San Dunes, Ilocos Norte, Philippines


Dunes in other planets and moons


Last edited by adedios on Sat Jan 27, 2007 4:58 pm; edited 3 times in total
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PostPosted: Mon Jun 05, 2006 9:02 am    Post subject: Understanding And Predicting Desertification Reply with quote

Source: New Mexico State University

Posted: June 5, 2006

Understanding And Predicting Desertification: Researchers Offer New Insights On Arid, Semiarid Landscapes

A team of researchers has developed a multi-faceted process to study arid and semiarid landscapes that takes into account the wide range of factors influencing changes that can result in desertification.

Led by Debra Peters, research scientist for the U.S. Department of Agriculture's Agricultural Research Service at the Jornada Experimental Range in southern New Mexico, the team of USDA and New Mexico State University researchers published their findings in the June 2006 issue of BioScience. The article is titled "Disentangling Complex Landscapes: New Insights Into Arid and Semiarid System Dynamics."

Almost 40 percent of the Earth's surface and 20 percent of the world's population are found in regions that are under threat from desertification, which can result in the loss of grass and degradation of soil as grasslands are converted into woody-plant-dominated landscapes.

Although many research methods exist to study various facets of this process, more complete understanding of desertification can be achieved by looking back in time at historic legacies, considering environmental factors and studying soil, typography and soil parent material. Also considered is the influence of wind, water and animals as they transport water, nutrients, soil particles, plant litter and seeds. The redistribution of those resources also is weighed in the landscape reorganization.

"Previously we looked at small areas and used that information to make guesses about the large area, to extrapolate to the big area, and that doesn't work very well when things are really complex," Peters said. "And so then we shifted to say, really, the complexity is what's interesting and important."

The researchers offer a six-step operational scheme to unravel the complex influences of these variables. The first step is to "look up" to assess the broad scale, then "look back" in time to determine the role of past events on the present landscape. Third, "look around" to consider adjacent spaces and the influence of wind, water and animals as connecting transport vectors. "Look down" to determine fine-scale properties and processes of the landscape, then integrate the information from broad scale to fine scale to determine the most important influences. Finally, "look forward" in time to the effects of variable environmental factors from the current landscape to the future.

Members of the research team also are part of the Jornada Basin LTER (Long Term Ecological Research) project funded by the National Science Foundation. They will now move into experiments and computer modeling to confirm their findings, integrate the information and make future predictions.

The Jornada Experimental Range is located in the northern portion of the Chihuahuan Desert, the largest desert in North America.
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PostPosted: Thu Jul 20, 2006 3:09 pm    Post subject: Sahara Desert Was Once Lush and Populated Reply with quote

Sahara Desert Was Once Lush and Populated

By Bjorn Carey
LiveScience Staff Writer
posted: 20 July 2006
02:07 pm ET

At the end of the last Ice Age, the Sahara Desert was just as dry and uninviting as it is today. But sandwiched between two periods of extreme dryness were a few millennia of plentiful rainfall and lush vegetation.

During these few thousand years, prehistoric humans left the congested Nile Valley and established settlements around rain pools, green valleys, and rivers.

The ancient climate shift and its effects are detailed in the July 21 issue of the journal Science.

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PostPosted: Tue Mar 06, 2007 7:29 am    Post subject: How can desertification control and development be reconcile Reply with quote

Institut de Recherche Pour le Développement
5 March 2007

How can desertification control and development be reconciled?

The pre-Saharan region of Jeffara, located in the South-East of Tunisia, is particularly exposed to the risk of desertification, like most of the arid or semi-arid regions of the Mediterranean Rim. It is also prey to deep socio-economic changes. This situation raises the major challenge of ensuring the balance between protection of the various ecosystems and the development of rural populations who live in them. Increasing economic diversification, accelerated and amplified in the context of rural policy reform and globalization of trade, has contributed to an intensification of desertification processes, in spite of the efforts nevertheless exerted by government organizations.

In order better to understand the processes involved in changes taking place in Jeffara and identify the limits beyond which the pressure of human activity causes an irreversible depletion of natural resources, a multidisciplinary research programme was set up in 2000 by the IRD, working in conjunction with local partners, over a study area of about 120 000 hectares (1). The approach adopted laid emphasis on the study of the interrelations between changes among local actors and their activities, on the one hand, and those of the environments, on the other. This revealed the issues, the assets and risks involved, as well as the conflicts that arise for the use of rare and fragile natural resources. The analysis results were used as a basis for recommendations drawn up to foster improved harmonization between desertification control strategies and the legitimate socio-economic development of local communities.

The rural populations of Jeffara have always known how to adapt themselves to the region’s restrictive environmental conditions by developing original practices in the use of resources and by adopting diversified family-based strategies (multi-activity based way of life, migration and so on). However, these old, traditional ways of regulating resource use are now being called into question. For 40 years now, pressure on resources has strongly increased, especially on water stocks. The pattern has changed, from concentrated production on small areas alongside extensive livestock rearing over much larger areas, to the development of several economic activities at once that depend on the same catchment areas. The same groundwater thus feeds drinking water supply, tourism, irrigation of large plantation plots (olive groves) and the food industry. In response to this pressure, systems to foster rain water and run-off water recovery have long been operating involving jessour (2) or, more recently, water and soil conservation schemes. The latter, set up along the main run-off pathways and their tributaries, slow down the run-off speed, thus favouring infiltration and recharging of the water tables.

In the Jeffara, the crop plantations established on weakened soils are increasingly fragmenting the land space. Such land is now reaching saturation level and soil degradation has intensified. Between 1974 and 1999, the areas cultivated increased by 180% in the mountains, 356% on the piedmonts and 798% on the central plain. This intensification of agricultural land uses stems partly from a State policy which since the 1960s has been resolutely in favour of land privatization, and has generated a "land rush". Arboriculture has therefore developed at the expense of livestock farming in the piedmonts and the plains, even on land where the terrain is unsuitable. This trend is a threat to a number of ecosystems which indeed are in danger of disappearing. Ecological studies reveal, in addition to the disturbing erosion of original vegetation assemblages, an increasing overall uniformity of the flora and hence a loss of biodiversity.

Such degradation can be checked by prohibiting the development of endangered natural environments for cultivation. However, real practical alternatives must in that case be proposed to farmers, in the agriculture sector, through maintenance of a certain diversified production in their holdings and enhancing commercial value of high-quality local or regional produce, but also by means of diversification of activities and of sources of revenue other than farming. This diversification would offer people improved flexibility to face up to climatic and economic hazards and enable them to manage better their families’ financial resources. In addition, the effort government has made in water management, through the CES, could be enhanced by schemes for desalinating brackish water and recycling waste water.

In the Jeffara, desertification control and socio-economic development do appear to be reconcilable, on condition that the specific nature of each environment and the social dynamics that make it up are taken as a whole, with a long-term viewpoint, incorporating economic and social contexts going beyond the regional territory. This issue is crucial for the future of the local people, who would no longer be obliged to leave their region in search of better standards of living.

Marie Guillaume-Signoret – IRD Translation : Nicholas Flay

1) This programme "Désertification dans la Jeffara tunisienne: pratiques et usages des ressources, techniques de lutte et devenir des populations", backed by the ‘Comité scientifique français de la desertification’ lasted 4 years. It involved the IRD, the IRA (Institut des regions arides), the regional commissions for agricultural development and the provinces of Médenine and Gabès. Following this study, the Jeffara region became one of the pilot sites in Tunisia for the ‘Réseau des Observatoires de Suivi des Ecosystèmes à Long Terme’ (ROSELT) promoted by the Observatoire du Sahel et du Sahara (OSS) in which the IRD is involved.

(2) Local name for the small traditional dams emplaced in ravines and encased valleys for upstream collection of water and the soil that it carries.

Key words: Jeffara of Tunisia, desertification, water resources, societies, environment, development.

For further information :

Contacts :

Didier Genin – IRD UMR 151 "Laboratoire Population-Environnement-Développement" (LPED), Université de Provence, case 10, 3 place Victor Hugo, 13331 Marseille cedex 3, France. Tel. +33 (0)4 91 10 63 57


Henri Guillaume – IRD UMR151, Représentation IRD Maroc, BP 8967, 15 rue Abou Derr 10000 Rabat Agdal, Morocco. Tel. : 212 (0)37 67 27 33


Mongi Sghaïer- IRA (Institut des régions arides), Km 22,2, Route de Jorf, Médenine, Tunisia. Tel. (00 216) 75 633 00


Contacts IRD Communication: Marie Guillaume-Signoret (coordinating editor), Tel.: 01 48 03 76 07, Email :; Press office, Tel.: 01 48 03 75 19, Email :

Reference :

"Entre désertification et développement - La Jeffara tunisienne". Scientific editors : Didier Genin, Henri Guillaume, Mohamed Ouessar, Azaiez Ouled Belgacem, Bruno Romagny, Mongi Sghaïer, Houcine Taâmallah. Co-edition IRD, Cérès Editions, IRA, 2006, 345 p.
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PostPosted: Fri May 11, 2007 6:34 am    Post subject: Drylands are not the same as badlands Reply with quote

Duke University
11 May 2007

Drylands are not the same as badlands

DURHAM, N.C. -- Drylands, where 38 percent of the world's population lives, can be protected from the irreversible damage of desertification if local residents and managers at all levels would follow basic sustainability principles, according to a panel of experts writing in the May 11 issue of the journal Science.

The study makes a point of introducing hope rather than the usual gloom, said James Reynolds of Duke University, who is the first author. "(Given) recent advances in dryland development, concerns about land degradation, poverty, safeguarding biodiversity and protecting the culture of 2.5 billion people can be confronted with renewed optimism," the report said.

Covering about 41 percent of the globe's land surfaces, drylands are arid and semiarid areas with scarce and unpredictable precipitation where about 2.5 billion people live off the land by raising livestock and growing certain drought-tolerant crops.

Between 10 percent and 20 percent of drylands are undergoing some degree of severe land degradation that is likely to expand in the face of climate change and population growth.

"These are serious problems, no doubt," Reynolds said. "And they could be exacerbated by climate change. But it doesn't always have to lead to negative outcomes. We are trying to take a more positive perspective, saying that adhering to some common-sense principles can really make a difference in understanding and managing these lands.

"The culture surrounding topics of desertification has always been embedded in this negativity and pessimism that 'woe is us,' " added Reynolds, a professor of environmental science and biology at Duke's Nicholas School of the Environment and Earth Sciences.

The report calls on managers to recognize that maintaining vulnerable and delicately balanced dryland systems involves a changeable mix of ecological factors and human ones.

For example, economic losses may force a marginal cattle raiser to increase his herd to make up the deficit, Reynolds said. And that decision may overtax the grass supply to the danger point, especially if a cycle of drought sets in.

It cautions that human and environmental changes in drylands evolve slowly, confounding efforts to manage for quick results. "What managers need to do is be more patient and not try to understand a system based on short-term dynamics," Reynolds said.

It argues that some slowly changing but key variables -- such as soil fertility -- have thresholds that, when crossed, can push systems into "a new state or condition," the report said.

Crossing thresholds don't necessarily mean a turn toward disaster. For example, the report cited the positive social and environmental effects of introducing piped water or solar-heated cookers in a remote village.

The report also encourages tapping the knowledge and memory of people who live on drylands. And it urges local and outside people and groups with vested interests to work together on maintenance issues.

"There have been a lot of misconceptions that people who live there are destroying the land, are ignorant about it and are using it in an incorrect fashion," Reynolds said. "That's really a problem of outside managers having little feel for what is going on.

"There's tremendous local knowledge among the native people who live there that needs to be taken advantage of," Reynolds said. "Then, mixed with some good solid science, there are many opportunities to improve these lands so they won't be degraded in the future."

For example, study co-author D. Mark Stafford Smith of the Commonwealth Scientific and Industrial Research Organization, in Canberra, Australia, has begun a program called Desert Knowledge that is tapping native Aborigines' millennia of experience on how to manage livelihoods in arid environments.

Reynolds directs a National Science Foundation-funded program called ARIDnet, through which he and his colleagues are testing their sustainability principles in case studies throughout Latin America.

Most recently, they have been working with farmers who raise a cereal called quinoa in Southern Bolivia. There they are assessing how the introduction of tractors is affecting traditional means of tillage, as well as the effects of the developed world's growing demand for the trendy grain.

The study was supported by the National Science Foundation; the Australian Government Cooperative Research Centers Program; the Commonwealth Scientific and Industrial Research Organization; and the Humboldt Foundation of Bonn, Germany.
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PostPosted: Fri Dec 07, 2007 2:36 pm    Post subject: Behind the Scenes:How Desert Dust Feeds the World's Oceans Reply with quote

Behind the Scenes:How Desert Dust Feeds the World's Oceans
By Pien Huang, Scripps Institution of Oceanography

posted: 07 December 2007 08:01 am ET

This Behind the Scenes article was provided to LiveScience in partnership with the National Science Foundation.

In mid-February, at the height of Austral summer, the sun in the Antarctic never sets. Nor did the work ever stop for University of Hawaii oceanography professor Chris Measures and his team of trace-metals oceanographers, who worked around the clock measuring dust from the decks of the Scripps Insitution of Oceanography research vessel Roger Revelle.

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PostPosted: Thu Jan 10, 2008 7:38 pm    Post subject: Desert Mystery Has Electrifying Answer Reply with quote

Desert Mystery Has Electrifying Answer
By Clara Moskowitz, LiveScience Staff Writer

posted: 10 January 2008 08:05 am ET

Sweeping sands across the Sahara and other dune expanses are blown by more than just wind, scientists have discovered. Powerful electric fields spring up near the desert floor and propel sand grains into the air.

By accounting for this electricity, researchers say they can design better climate change models, and even explain features of the dust on Mars.

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