Namib/Kalahari (Southern Africa): Deserts
1. Zoom from the Salar de Uyuni salt flats to the Namib/Kalahari.
2. Along the west coast of Africa is a place, Namib Desert, that is one of the most
inhospitable (no volcanoes, no acid lakes) – incredibly dry, and has been for
over 50 million years.
a. The shoreline has been called Skeleton Coast
i. Bushmen of the Namibian interior called the region "The Land
God Made in Anger"; Portuguese sailors called it "The Gates of
Hell".
ii. More than 1000 shipwrecks along the coast
iii. Thick fogs; rocky shoals; but not a drop of freshwater
iv. Because of constant heavy surf, almost impossible to get back
off the beach once a (human-powered) boat lands there.
v. Also many skeletons of whales remain from days of whaling
b. The Namib gets less than 1 cm of rain/yr. Western part gets even less
– 0.5 cm/yr. If you are stuck there, there is no way to survive. The area
is totally uninhabited.
c. Just over a ridge of mountains, the Namib escarpment, is another
desert, one of the largest – the Kalahari, but it is totally different in
character.
3. Describe a dry desert
a. We already visited the world’s largest desert: Antarctica. Also visited
some high, cold deserts, like the Gobi and Atacama.
b. Some are huge – describe Sahara and Arabian deserts – but many can
be small
c. Hot deserts have a very different appearance.
i. Sand dunes (though only about 20% of hot deserts)
ii. More common is desert pavement. How does it form?
1. Wind – blows away lighter sand, leaving rocks behind
2. Freezing and thawing; wetting and drying
d. Extreme temperature changes – in places like the Kalahari
temperatures can be freezing at night in winter, but still be hot during
the day.
i. Why? The reason is water, or lack of it.
1. Explain how water vapor is the strongest greenhouse
gas, and clouds block incoming sunlight during day (less
hot), but water vapor absorbs radiated infrared energy
from the surface at night (less cold) – has a moderating
effect.
2. In a desert, with no water vapor in the air, the sun heats
the surface greatly during the day, but the heat escapes
quickly at night
ii. How about wetting and drying?
1. Though rain is rare, you can still get storms on occasion.
2. In fact, many people die from flooding in deserts
[explain]
e. Some of the least inhabited places in the world; remarkably there are
people who live in the deserts – Bodouin, Tuareg
f. Growing interest in desert regions
i. Mineral resources: many useful resource form as evaporates
(sodium nitrate – used as fertilizer and in gunpowder; gypsum,
etc.), and salts washed into playas (we saw lithium in the last
lecture)
ii. Sites for solar energy: lots of sunlight and open areas! A good
combo.
1. Talk about solar plants in the Mojave.
4. Hard to pick a single desert.
a. Sahara is largest.
b. Rub al Khali (southern 1/3 of Arabian peninsula) is the largest Sand
Sea.
c. Atacama is the driest (average rain over the whole region is 1 mm/yr;
some weather stations have never received any rain; no rain during
habitation, since 1570; mountains should have glaciers on them, but
there is no snow to make ice)
d. But Namib is Oldest; and so strange to be next to so much water, but
be so dry. It also has the tallest sand dunes in the world, which are a
striking red color.
e. Explain the reason for the desert:
i. Prevailing wind blows east to west
ii. As moist air from the Indian ocean rises up over the
Drakensburg mountains of South Africa (east coast) it cools
and loses its moisture
iii. It is dry when it crosses the Namib Escarpment, and as it drops
and warms, it even absorbs any available moisture. This is why
it is drier near the coast than even a bit inland.
5. Though Namib is incredibly dry throughout, there is still a lot of variation if
you were to visit.
a. The largest sand dunes in the world are in Sossusvlei region. The rich
ochre sea of sand, rise to almost 1,000 feet (305metres), which is 300
feet (91metres) more than their nearest rivals in Arabia.
i. The older the dune, the brighter the color; from slow iron
oxidation and tiny fragments of garnets.
ii. These dunes refract spectacular colors with the changing light
and turn from burnt orange through reds to deepest mauve.
b. The Fish River Canyon in southern Namibia is reminiscent of the
Grand Canyon in Arizona.
i. Rock stratas of purples, pinks and greys stretch along a 100mile (161km) course.
ii. Drops vertically by 1,800ft (550m) out of a flat arid plateau
without any warning
iii. at some points it is 17 miles (27km) wide!
iv. According to the San Bushmen the many twists and curves
were carved by the serpent, Kouteign Kooru, in an attempt to
escape capture.
c. Right along the coast, there can be thick, blinding fog. This is where
the dry air meets the cold moist air from the cold Benguela current
that runs up along the coast.
i. The moist air is pushed down by the hot dry air from the
Namib; as is falls and warms, it condenses into thick banks of
fog
ii. This fog is the only moisture that some parts of the desert ever
get, and life has evolved to adapt to it
iii. Even though the desert is incredibly dry and the total biomass
is low, the difficult conditions cause a very high degree of
biodiversity as life has adapted to the harsh conditions.
1. Many species of beetles have protrusions that act as
nucleation points for condensation from the fog: water
droplets form on their bodies!
2. Plants do the same.
3. The body temperature of Gemsboks (oryxes) increases
in the heat – up to 40C (104F)
6. Across the Namib Escarpment, in the Kalahari, life is much more plentiful. If
you ever saw the movie The Gods Must be Crazy or the animated movie The
Lion King, then you have a sense of what this area looks at.
a. meerkats, lions, jackals, buffalo, etc.; and bushmen too.
b. Technically not a desert – there is enough rainfall that it is a semi-arid
region (steppe).
c. There are regions where the Kalahari is a true desert.
d. But the most interesting region is to the north, where the Okavango
River empties into the desert and disappears.
e. Heavy rains in January in Angola flow into the Okavango, which
swells. 2-4 months later the water reaches the Okavango delta
f. 250 km x 150 km; the Kalahari is in an ancient giant lake bed – Lake
Makgadigadi – and is very flat; the whole topographical variation
across the delta is about 6 feet.
g. A single clump of trees can start to accumulate silt and more
vegetation and develop into a small island; the delta is dotted with
them. The trees usually start on termite mounds.
h. Only one larger island – Chief’s Island – which used to be the sole
hunting grounds of the local chief. Is a refuge to animals at the height
of the flooding.
i. “Food” has a negative connotation in most of the world, but not here –
it is rejuvenating and life-giving. Before then, elephants have to did
down deep to reveal water.
j. Most of the water ends up evaporating, but some seeps into the
ground.
7. Top 5:
a.
b.
c.
d.
e.
[Antarctica (already done); Sahara (next lecture)]
Arabian
Gobi
Atacama
Great Victoria Desert (Australia)
Questions:
1) Along the west coast of the US the situation is reversed: there is lush
vegetation from the coast up the sides of the coastal mountains, and dry
desert area east of the coastal mountains. Why do you think this is reversed
from the Namib desert?
2) How do you think life has evolved to adapt to a situation at the Okavango
delta where there is a lot of water for a brief period of time, and arid
conditions the rest of the time?