Geoscience Reference
In-Depth Information
Channel avulsion was also a problem for the Sumerian civilization on the alluvial plain
called Mesopotamia - 'the land between two rivers' - known for the rise and fall of its
numerous city states. Most of these cities were situated along the Euphrates River, prob-
ably because it was more easily controlled for irrigation purposes than the Tigris, which
flowed faster and carried much more water. However, the Euphrates was an anastomosing
river with multiple channels that diverge and rejoin. Over time, individual branch channels
ceased to flow as others formed, and settlements located on these channels inevitably de-
clined and were abandoned as their water supply ran dry, while others expanded as their
channels carried greater amounts of water.
Pathways for exploration
The straightforward pathways offered by rivers have always been used by people arriving
to explore new lands. Archaeological evidence suggests that early humans penetrated an
island later to become known as Britain along its major rivers during the Palaeolithic peri-
od or early Stone Age, later spreading out and settling areas further from the river banks.
Similarly, some 6,000 years ago, Neolithic tribes used river courses to enter Central Europe
from the southeast. In both cases, river valleys offered plentiful supplies of essential re-
sources for these early settlers: water, fish, and floodplains rich in game for hunting.
Many hundreds of years later, the great river systems of North America enabled European
pioneers to explore vast new territories, opening them up to trade and eventual coloniza-
tion. In the 16th century, a succession of French traders, explorers, and missionaries were
the first Europeans to arrive in the Great Lakes region, following the exploration of the
St Lawrence River by their fellow countryman Jacques Cartier in the 1530s. Dispatched
by the king of France, their main purpose was to chart the river systems as highways that
allowed access to a new continent. These were often the only thoroughfares through the
otherwise impenetrable forests of North America, traversable by canoe as liquid highways
or dogsled when many tributaries froze over during the winter.
By 1804, when Meriwether Lewis and William Clark were sent by US president Thomas
Jefferson to explore, survey, and document an immense swathe of North America that he'd
just bought from the French - the Louisiana Purchase - rivers were still the easiest routes
to follow. Lewis and Clark's expedition took them up the Missouri River, across the Rocky
Mountains, and down the Columbia River to the Pacific Ocean. Their expedition and the
information they brought back, particularly about the Pacific northwest, played a pivotal
part in the westward thrust of US expansion.
