NOTE: This Earthcache is at a border crossing. Please check with appropriate border authorities to determine the current legal ways of accessing the area or border crossing here before planning to visit this cache.
Introduction to the rivers
The Zambezi River starts as a small trickle of a natural spring in Mwinilunga District of Zambia. As it travels, it collects more water and grows larger. By the time it reaches Victoria Falls at the nearby gorge at the Zambia/Zimbabwe border, over a million cubic metres of water per minute go over the edge. As the force of this river travels through the landscape, it alters it in fascinating ways.
The Chobe River, on the other hand, starts in Angola (at Mount Tembo) the same way it finishes in Botswana - as a complex maze of small channels and marshes that meander through the landscape. During the months of February to May, the water levels of the Chobe rise considerably due to overflow from the Zambezi River. This extra influx of water is known as a backflow, and it covers the immediate surrounding flood plains and small islands that are present near the Chobe.
Your location
This spot is located right where the Chobe flows into the Zambezi. There is also another unique feature of this location - it is where four countries meet: Zambia, Zimbabwe, Botswana, and Namibia.
You are welcome to access this Earthcache from anywhere in the vicinity that allows you to see both the Botswana shore and the Zambia shore. However, if you are not already in Botswana, you will need to cross the border via boat or the bridge. Please ensure you cross the border legally and with the required passport or anything else that is requested. Any location where you can see the plants on both the Botswana side and on the Zambian side (by using binoculars) will allow you to answer these questions.
Where two rivers meet: what materials do they bring?
This Earthcache will get you to examine the ground materials, vegetation, and water levels on the Botswana side of the river as well as to look across at the Zambian side. You will become an "Earth detective" as you look for clues to the underlying type of soil materials beneath your feet on the riverbank.
Because of the confluence of two rivers here, and their different currents, different types of soil and materials have been deposited in different amounts on each side of the river. Only the topsoil layer is visible, but by observing specific features around you, it is possible to uncover clues to some of the underlying layers of earth materials. According to an ecological survey done of the area, here are the types of materials found in this exact location:
Topsoil: Dark brown silty sand with small pebbles.
Alluvial Sand: Alluvial sand is a general term for a mixture of clay, silt, sand, gravel, mud or similar unconsolidated material deposited by a body of running water. This type of sand or soil is loose and not packed together.
Alluvial Gravel: Pebbles of sandstone and basalt from 3-5cm in diameter.
Chalcedony: Greenish-grey coloured hard rock.
Volcanic Sand: Reddish brown-to-black coarse sand with fragments of basalt
Basalt: Hard, weathered, reddish-brown rock.
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How can you tell which side of the riverbanks have much larger deposits of alluvial sand, without digging deep into the ground? Because of the loose, thin quality of alluvial sand, areas that have larger deposits of it have more difficulty sustaining vegetation, even in areas with high rain and that are near rivers. Therefore, locations that have large deposits of alluvial sand will have plants that are thinner and dryer, while locations that have less alluvial sands allow the plants to grow thicker, lusher, and greener.
Please examine the vegetation on the Botswana side, and use binoculars to see the vegetation on the Zambian side if you are not crossing the border. Send me an email with answers to the following (do not post answers in your log) in order to claim a find.
1. Now that you have examined the vegetation on each side, and read the above information, which side do you think has more alluvial sand deposits, and why?
2. The Botswana side is the only side with chalcedony deposits. Examine the sand at your feet on the Botswana side. Can you see evidence of the chalcedony? Why or why not?
3. You will notice that for several metres inland from the shore, you are standing in sand and not soil. How do you think both rivers contributed to this feature of the landscape?
4. During the time of year that you are visiting, the Zambezi may or may not be overflowed into the Chobe. Looking at the landscape at the riverbank, how can you tell why the riverbank is the way it is during the time of your visit?
5. **Required**: A photo of your GPS, phone, or other random item (your keys? your hand? a souvenir?) with the Kazungula Border Ferry or the newly built border bridge in the background. This will help me verify that you were actually there.