Borders, Rivers and Mountains
Why the Caspian defies definition, how a channel links two great river basins, and what really keeps the Rhine busy. 50 questions on the world's dividing lines.
Try 3 questions
1. The Paraná River forms part of the border between Paraguay and Argentina before reaching the Río de la Plata estuary. Which feature explains why the Itaipú Dam was built on a stretch of this river shared by two countries?
- The river's mouth lies nearby, so turbines can use tidal inflow from the Atlantic
- The river drops sharply over a basalt escarpment there, giving high hydroelectric potential
- The river widens into a shallow floodplain there, making reservoir storage cheap
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Answer: The river drops sharply over a basalt escarpment there, giving high hydroelectric potential
The Itaipú site sits where the Paraná cuts through hard basalt with a steep gradient (near the former Guaíra Falls), providing the head needed for large-scale hydroelectricity.
2. Chile and Argentina share one of the world's longest land borders. Which principle has historically guided most of its demarcation?
- The southern edge of the Atacama's salt flats extended eastward
- The line of the highest Andean peaks and the continental watershed divide
- The 70th meridian west, surveyed from north to south
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Answer: The line of the highest Andean peaks and the continental watershed divide
The 1881 boundary treaty set the frontier along the highest Andean summits that divide the waters, a principle that later caused disputes where peaks and watershed did not coincide.
3. Why does the Nile support dense settlement across Egypt while rivers of similar length elsewhere do not anchor comparable populations?
- It carries water from humid highlands through an otherwise arid belt
- Its delta sits below sea level, trapping rainfall year-round
- It flows northward, which slows evaporation along its course
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Answer: It carries water from humid highlands through an otherwise arid belt
The Nile is an 'exotic' river: its flow originates in the Ethiopian Highlands and equatorial lakes, delivering water across desert that receives almost no rain.
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