The Earth Story

Pretty Grand Although this landscape may seem familiar to lovers of the U.S. National Park System, this is a site far from the canyonlands of the Colorado River. This is the Fish River Canyon, located in southern Namibia on the western coast of Africa. The Fish River is Namibia’s longest river. It originates in the northern part of the country, travels most of the country’s length, and takes a path with wide meanders as it enters Richtersveld National Park. The river meanders back and forth by several kilometers and wide meanders are common for rivers that form on nearly flat topography. Therefore, this canyon sits on a site of an ancient river that slowly wound its way over the surface until it locked itself in place.

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Rafting trip on Bakota gorge downstream of Victoria Falls Zambezi river

Patterns of organic energy

Mountains are energetic places, from the slow grinding tectonic rise to the powerful forces of erosion that they invoke by their presence and height. They attract rain and snow by forcing air to rise and its moisture to condense into clouds, and then either store it as glaciers or lakes or get carved out by the flowing water (liquid or solid) as it runs down following gravity towards the sea. Said carving results in a variety of features, such as deep gorges and U shaped glacial valleys, and, of course, in a vast amount of sediment that also journeys towards the sea (until the inevitable moment when the tectonic event ceases, and erosion wears them away to a flat and boring peneplain).

Much of the larger sediment moves in bursts when more powerful weather events move large amounts, while the background rate of downward flow is fairly gentle. Every year in the Himalaya for example, when the monsoon strikes, roads all over the region are washed away in landslides as the sediment saturates and falls downwards. An ice age is another large spurt at a longer timescale in a rock's journey from mountain to deep sea sediment. This means that a particle of sediment may well spend quiet aeons in storage in a sediment reservoir, awaiting the conditions powerful enough to remobilise it into a new phase of the journey.

The photo depicts a region near the India/China border, with one of the main ranges at the top. Sediment from the mountains, much of it probably from the last ice age, has been distributed into alluvial fans, the large flat areas just to the south of the chain. As the streams carrying it emerge from the steep mountain area onto the flatter fan, their energy decreases, and they form braided rivers and dump alot of their sediment, since they lack the energy gradient to carry it any further. Such melt water and rain as the summer provides has carved a lovely dendr itic (tree like) drainage pattern and a couple of deep gorges to complement the energetic pattern. .

Loz Image credit: NASA

http://earthobservatory.nasa.gov/IOTD/view.php?id=85721&src=fb

Fish River Canyon

The Fish River Canyon, located in Namibia, is the largest canyon in Africa and the second largest in the world. It is one of Namibia’s most visited tourist attractions.

Encompassing a total area of 5900 square kilometres, the canyon is made up of a massive gorge which approximately 180 km long, 27 km wide and over 500 meters deep in some places. While it’s considered to be small when compared to the Grand Canyon in the US, it is still a sight to behold.

The forces of water, wind, ice, and gravity have contributed to the 650 million year formation of this masterpiece. The Fish River Canyon is made up of a wider upper canyon and a narrow lower canyon. The lower canyon was formed after erosion had finally worn through the hard *gneiss bedrocks.

650 Million Years ago, a north-south *graben was formed by plate movement. The ancient Fish River flowed along this graben and eventually eroded the sedimentary rocks along the graben edges away, leaving a flat plain which is now the upper canyon. Glaciation during the Karoo Ice Age (360 – 260 million years ago), caused the canyon to further deepen.

When Africa and South America separated as Pangaea broke up, Africa's elevation rose considerably, increase in the gradient of the Fish River. This steeper gradient and faster water flow increased the power of the water and allowed it to begin eroding the lower canyon into hard, metamorphic gneiss* bedrock that had previously resisted erosion, cutting the inner canyon seen today.

Different colours of rock strata can be seen along the length of the canyon.

The river is generally dry but floods in the region’s rainy season which is usually between January and April.

The area is known to be a semi-desert with temperatures rising up 50 degrees Celsius during the day and dropping to just over 30 degrees Celsius at night. The average annual rainfall is 100mm. In the winter months, temperatures can be expected to drop below 0 at night, yet it can reach well above 30 degrees Celsius during by midday. Despite this temperature fluctuation, there are over 50 species of bird life spread throughout the canyon. In the lower regions, antelope and baboons can be seen. Sightings of leopards and mountain zebra have also been reported.

*gneiss – high grade metamorphic rock

*graben - is a depressed block of land bordered by parallel faults

-Renesh T

Image source http://bit.ly/1G9Um5H

References/Further reading http://bit.ly/1FYofAu

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Verdon Gorge, France