Sahara desert

Discussion in 'Earth Science' started by yaracuy, Mar 29, 2011.

  1. yaracuy Banned Banned

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    Do the boundary of the Sahara desert goes through cycles ?

    Could there be as the Atlantic ocean gets warmer the desert will bloom ?

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  3. drumbeat Registered Senior Member

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    A few thousand years ago the southern edge of the desert was much further north.
     
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  5. ULTRA Realistically Surreal Registered Senior Member

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    Its growing. In fact parts of southern Spain are slowly becoming desertified now.
     
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  7. Rocks Registered Member

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    Part of the reason it is a desert is geography more than overall climate. The area inland is so vast that most rain that will reach that part of Africa will get spent long before those clouds can reach the interior.
     
  8. yaracuy Banned Banned

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    Would you believe there have been crocodiles in the area which is now desert
     
  9. yaracuy Banned Banned

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    Siberia is also way deep yet the desert is further south in Mongolia and China

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  10. ULTRA Realistically Surreal Registered Senior Member

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    Climate change is nothing new. It's just happening much faster than it normally does.
     
  11. Rocks Registered Member

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    Siberia is on the Arctic Ocean, so isn't exactly "way deep" and its southern region is quite mountainous, so again, the reasons for this are geographic/topography.

    Very true.
     
  12. Cifo Day destroys the night, Registered Senior Member

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    Well ... it shifts.

    Bordering the Sahara to the south is a belt of land called the "Sahel" (literally "shore", but meaning "borderland" in this sense). Like the "shore" we know, it's a kind of transition zone between the Sahara and the more vegetative lands to the south. The Sahel also shifts.

    Contrary to what the movies portray, the Sahara also consists of relatively unknown rocky fields (Arabic hamada) and extinct rocky/volcanic mountain ranges (such as the Ahaggar and the Tibesti) along with those popularly portrayed salmon-colored shifting sand dunes (Arabic erg). The rock fields and mountains don't shift like the dunes.

    The semi-arid Sahel receives enough rain to allow enough vegetation to grow that humans can subsist in the region, although sparsely. As the rainfall has fluctuated over the years, so have the areas where humans can live.

    I don't know about "cycles", but the human destruction of vegetation and the dryer climate in recent years has resulted in (what could be described as) the Sahara and the Sahel "shifting" southward. Basically, desertification has been occurring.
     
  13. Trippy ALEA IACTA EST Staff Member

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    The Sahara desert goes through cyclic 'wet' or 'green' periods, where the area currently occupied the by the Sahara becomes a Savannah.

    It has been known to go the other way as well, with periods where the Nile river corridor has been non existant because the Nile has (for one reason or another) stopped flowing (as indicated on the wiki link I am providing),\.

    Sahara Pump Theory on Wiki
    Neolithic Subpluvial on Wiki
    Wet phases in the Sahara/Sahel region and human migration patterns in North Africa

    My (somewhat limited) understanding is that it seems to be linked to the migration of Monsoon winds in response to melting ice-sheets, and the changes in atmospheric circulation that those result in as part of the glacial cycle.
     
  14. yaracuy Banned Banned

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    I see the graph of fluctuation in Ice period on 120k 30 k and the last 16k which is a relative narrow band it is called Heinrich event, Well As you implied the desertification was a function of the water temperature in the Atlantic ocean
    Thanks for the reference .

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  15. yaracuy Banned Banned

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    Thank you for the map.

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  16. yaracuy Banned Banned

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  17. Fraggle Rocker Staff Member

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    The Gobi Desert in China and Mongolia is also expanding. At the current rate, 1400sqmi/3600sqkm of grassland become desert every year. This is attributed to deforestation and overgrazing, as well as simply depletion of the water table as it is pumped into the cities.

    Being so far north, there are many differences from the Sahara. Although the temperature can reach 100F/38C in July, it can also fall to -52F/-47C in winter. Rainfall is higher at 8in/200mm per year, although still well within the definition of "desert" at less than 10in/250mm. Most of the rain falls in summer but a bit of snow in winter is not uncommon.

    When the current cyclical warming trend reaches its maximum (probably in another five or ten thousand years unless we find a way to accelerate it even more than we have, arguably, already done), the icecaps at the poles and the permanent glaciers on the high mountains will have melted. All of that water will be freed up to evaporate into the atmosphere. This will result in a higher average rate of rainfall than we have today--although weather patterns will ensure that this increase is not spread evenly over the planet. All that water has to end up somewhere, so sea level will rise by something like 100ft/30m, submerging the coastal cities where a high percentage of the world's population now lives, as well as places like Florida, some lovely islands, and much of Bangladesh.

    We have never experienced the opposite--maximum cooling--during recorded history, but our species has had to deal with it more than once. Around 60KYA the average global temperature was several degrees lower, enough to lock up far more water in the icecaps and glaciers than we're accustomed to today. Sea level fell by about 400ft/120m, and rainfall was so low that there was a drought in Africa. The resulting famine was so dire that some of our desperate ancestors decided to try walking out of Africa into Asia in search of better lives--a much shorter walk than it would be today. They eventually reached Australia, which due to the vagaries of weather patterns had a delightful climate with a cornucopia of edible plants and animals. They settled there and became the Native Australians. A few established colonies along the way and traces of their DNA can still be found in some of the coastal populations of South Asia. (The rest of the continents were settled by a second wave of migration 5-10,000 years later.)
     
  18. yaracuy Banned Banned

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  19. Skeptical Registered Senior Member

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    While there are plenty of eco-disaster mongers who will tell us that the Sahara is growing bigger, the evidence indicates more a cyclic change.
    http://news.nationalgeographic.com/news/2009/07/090731-green-sahara.html

    A number of episodes of greening of the Sahara at the fringes are on record, during years, and even a decade or more, when rainfall is higher than average.

    The Sahara has been much greener in the past, as discovery of human remains, and rock paintings of animals shows.
    http://ngm.nationalgeographic.com/2008/09/green-sahara/gwin-text/2
     
  20. Dinosaur Rational Skeptic Valued Senior Member

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    I think that almost all of North Africa was once capable of supportng agriculture. Perhaps as late as the Punic wars between Rome & Carthage.
     
  21. Michael 歌舞伎 Valued Senior Member

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    Actually I read it was the rise of Himalaya Mountains. I don't think they'll be residing anytime too soon - or at least not before Africa drifts into another continent a few hundred million years from now...
     
  22. Shadow1 Valued Senior Member

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    .

    it was actually forests, being destructed over time for agricultural lands, however, i'm not sure if all of it, but, idk, there's alot of forests fossils in the desert, and animals and rivers too
     
  23. Honeyb35 Registered Member

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    How do people live in the Sahara Desert?
     

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