3.1 a) Low Latitude Desert Case Study- Namib Flashcards
(25 cards)
What are low latitudes?
Low latitudes are those locations found between the Equator (0 degrees N/S) and 30 degrees N/S.e
What type of desert is the Namib?
The Namib is a cool coastal low-latitude desert and an immense expanse of relentlessly moving gravel plains and dunes of all shapes and sizes that stretch along the entire coastline. The most widespread and dominant type of desert sand dune are linear dunes, with crescent shaped dunes common along the coast and clusters of star dunes, such as the towering horseshoe of dunes at Sossusvlei, found in the eastern reaches of the sand sea.
What is the importance of the Namib?
The Namib is arid and is almost totally uninhabited, except for a small number of scattered towns. It is important because of the trade routes that cross it, its mineral deposits, the fisheries of the bordering sea, and its increasing utilization for recreational purposes. A large section of the desert makes up the Namib-Naukluft National Park, Africa’s 3rd largest protected area.
What does the name ‘Namib’ imply?
The name is derived from the Nama language, implying ‘an area where there is nothing.’
How long does the Namib extend along the Atlantic coast?
The Namib extends for 1,200 miles (1,900 km) along the Atlantic coast from Namibe in Angola southward across Namibia to the Olifants River in the Western Cape province of South Africa. It reaches inland 80 to 100 miles (130 to 160 km) to the foot of the Great Escarpment. The southern portion merges with the Kalahari on the plateau atop the escarpment. The Namib desert runs North to South along the coastline of Namibia and is therefore present in each of the three zones.
What are the three zones of the Namib?
The Namib is divided into three successive north-south-trending strips: the very narrow coastal region along the Atlantic, strongly subject to marine influences; the Outer Namib, occupying the rest of the western half of the desert; and the Inner Namib, constituting the eastern portion. The boundaries between them consist of broad transition zones.
What characterizes the southern Namib?
- is characterised by winter rainfall and succulent plants falling into the northernmost extension of the Succulent Karoo biome of southern Africa, notably from the Orange River in the south and to the coastal town of Luderitz further north.
What defines the central Namib?
an area confined by the Atlantic Ocean in the west and the escarpment to the east, sandwiched between the Kuiseb River in the south and Huab River in the north. The central Namib provides a number of habitats for plants, notably expansive gravel and gypsum plains, rocky outcrops and dry river courses with associated drainage lines.
What is unique about the northern Namib’s climate?
is a very dry place with low and unpredictable ranges and amounts of rainfall varying from zero to over 100mm. Rain and the chances of it become less towards the coast. It is fog that provides reliable moisture and as with the central Namib area, a fog belt can stretch some 20 and 30 km inland and on occasions further inland.
What is the average weather cycle in Namibia yearly?
December to March: it is generally hot throughout the country. The main rainy season starts in January (often with thundershowers). The vegetation turns into a lush green.
April to May: rains might still occur. The temperatures slowly start to drop.
June to September: it is winter in Namibia. No more precipitation is received (except in the far south - in the winter rain areas) and during the day temperatures are moderate to warm. The nights are severely cold, in the inland and desert overnight frost occurs. The vegetation changes from green to brown.
October and November: temperatures rise increasingly and it gets hot again. The so called “little rainy season” starts and brings a most welcome end to the long dry period.
What is the temperature range at the coast of Namibia?
At the coast there is little difference in temperature between day and night or between winter and summer due to the moderating effect of the sea (see diagrams). Temperatures are usually between 10 and 16 C. Along the inland margins, summer temperatures normally reach the low 30s C. Only in areas sheltered from the cooling sea breeze (lee sides of mountains and bottoms of canyons) do temperatures frequently approach those expected in low-latitude deserts-i.e., in excess of 38 C. Freezing temperatures occur occasionally along the inner edge of the desert. A few days each year, usually in fall or spring, berg (mountain) winds blowing from the east bring high temperatures (above 38 C) together with dry air and clouds of dust, across the desert to the coast itself.
* At the coast the diurnal range of temperature is low, and there is no difference between winter and summer because of the moderating effect of the sea. The land absorbs heat quicker from the sun than the sea, therefore the air over the land heats up as the absorbed heat is radiated. This hot air begins to rise, and the cooler air surrounding the sea moves to take its place. The land cools quickly once the sun sets, however the water doesn’t, it can radiate its stored heat into the air, this rises and the cool air over the land takes its place.
* Temperatures are usually 10-16 degree, however further inland it can reach up to 30 degrees.
* The sea breeze cools the air down, and only places with shelter from this, such as the lee sides of mountains, are able to reach higher temperature, up to 38 degrees.
How does precipitation occur in the Namib?
The land absorbs heat from the Sun more quickly than the water does. The air over the land becomes warmer as some of this absorbed heat is radiated back into the air. The warmer air begins to rise, and the cooler air over the water moves in to take its place.
As the Sun goes down, the land cools off quickly, but the water does not. The water radiates some of its stored heat into the air, and this warmed air begins to rise. The cooled air over the land moves in to take the place of the rising warm air over the water.
The rare rains occur usually as short-lived torrential thunderstorms. Unique meteorological phenomenon distinguishes the Namib from all other deserts. Erratic annual rainfall compounds the regional aridity. Rain can only fall over the Namib Desert when warm, moist air is blown onto the eastern side of the African subcontinent by south-east trade winds. It is highly seasonal and coincides with weak South Atlantic anticyclone activity.
* Erratic and rare rainfall, usually in the form of thunderstorms.
* Rain can only occur when warm, moist air is blown towards east Africa as a result of south-east trade winds.
* Precipitation is highly seasonal- can be related with the south Atlantic anticyclone activity.
What is the impact of high wind speeds in the southern Namib?
In the southern Namib, continuous high wind speeds are channelled through valleys. They batter the landscape without respite, forcing the surface of the earth to become uncharacteristically dry. In particular, the Sperrgebiet experiences the highest wind speeds ever recorded on earth.
* In the southern Namib, high speed winds can pass through valleys, this creates the venturi effect, where the wind speeds up as it enters narrow spaces.
* This high speed wind affects the moisture of the earth, and the soil can become very dry.
* The Sperrgebiet experiences the highest wind speeds ever recorder on earth.
What role does coastal fog play in the Namib?
This regulates the climatic extremes. Desert rainfall is sporadic and unpredictable. Fog isn’t. The cold ocean Benguela current that moves northwards carrying cold water from the Atlantic Ocean which cools the relatively warmer descending air from the Hadley cell on the Namib coast. This prevents the air from rising and condensing at higher levels forming clouds as a temperature inversion is created. Instead mist or fog is created at 300m (cloud at low levels) as the condensation process happens nearer to ground level. The onshore winds (winds blowing from the sea towards the land) carry this fog inland. The relatively warmer temperatures inland by midday result in the fog dissipating. Warmer air can hold more water vapour before becoming saturated so relative humidity is low and rain does not occur. Fog is a most reliable source of moisture and although the amount of water captured from a blanket of fog is relatively small, plants and animals have adapted to the amounts on offer. But like rain, it is life- giving.
What is the significance of soil depth in Namibia?
A high degree of dissection, more incisions in the soil from streams and rivers. This creates a broken landscape decreasing cultivation for crops.
The deeper the rooting depth, the larger the capacity to cultivate crops as the availability of soil and moisture. is higher, however some vegetation has adapted to shallow soils. A high inflation rate decreases the ability for plants to gain moisture and increases surface run off.
Rooting Depth- Many parts of Namibia have shallow sols- unfavourable for crop production, but natural vegetation has adapted to the situation. Areas of deeper soil have potential for crops and a higher population of people.
Infiltration rate- most water percolates- lost to groundwater storage- water holding capacity
The Namib desert is a large expanse of hyper arid desert plains and sand dunes. Therefore, its soil plays a massive factor in the construction of its geology.
What defines the Namib desert’s water situation?
Is a dry climate- reflected by the almost complete lack of water on the surface. Most rivers flow underground and/or are dry for most of the year. When they are not they usually drain into endoreic basins, without reaching the sea. The Swakop and Omaruru are the only rivers that occasionally drain into the ocean- tributaries. High relief decreases towards the coast.
What are the main landforms in the Namib desert?
- Mostly aeolian landforms- lack of water formed through aeolian erosion and deposition
Rock Bridge at SpitzKoppe: - Over 700 million years old
Dune 45: - In Sossusvlei area where red orange dunes can be found
Spitzkoppe inselberg and pediment: - 1728m above sea level
- Called the Matterhorn of Namibia due to its distinctive shape
- The landforms found within the Namib are all aeolian landforms.
- Yardangs are formed from the high speed winds and the impact of the venturi effect. A yardang field can be found in the northern Namib to the south of the cunenne sand sea. The direction of the prevailing wind turns the beds of soft rocks into troughs through abrasion. The hard rocks are undercut and they stand up as narrow ridges which are yardangs.
- The rock bridge at SpitzKoppe- stands out from the flat desert plains.
- Dune 45 found in the Sossusvlei area. Is a product of aeolian erosion and deposition.
- SpitzKoppe inselberg and pediment. Volcanic processes can leave behind a body of hard rock inside a body of soft rock. This soft rock can be eroded down to form a plain and leaves behind the isolated mountain of hard rock. After being exposed, the erosion of joint blocks and exfoliation can wear the rock down. Over a longer period of time, a talus slope and pediment can form.
What are the sediment and processes focused on in the Namib?
Plants have adapted to capture moisture from fog and survive in shallow soils.
grass offers a crucial sanctuary for wildlife.
Star dunes can be up to 300m tall, iron oxide in the sand gives it an orange glow.
- mass movement by slumping and landfalls
high diurnal range
Seals can survive high winds- blubber. Vulnerable to Jackals- Cape Fria
Barchan dunes- tallest in the world. crescent shaped which merge into a vast lined dune system further north South. South west and east winds affect this.
winds are the strongest in Africa
for lizards, under the sand is 50 c cooler than Sand Surface temperature. On the sand must rotate listing up legs and arms to Cool Body Surface temp.
Fog drifts inland:
- condensation is greatest on the summits of the dunes?
- leaves of dune grasses channel the drops of condensation to their roots.
- Dampness of fog acts as a break on the movement of sand.
‘KUISEB RIVER:
?Strong-sand can be pushed all the way back down the coast.
?millions of tonnes of rocks and sediment is washed away.
Sediment carried 200km in south Atlantic ocean north, before being carried inland.
Orange river- erodes mountains + rocks quickly-is very powerful
What is the type of fog produced in the Namib desert?
advection fog
How much annual rainfall does walvis bay recieve?
23mm
What is the mean monthly temperature at walvis bay?
11-24 degrees
How high are the dunes in the Sossusvlei region?
300ms
Linear dunes run hundreds of kms from walvis bay to which river?
Orange river
How long did it take for the sands to have been transported by winds 400 kms north to walvis bay?
1 million years
