Geoscience Reference
In-Depth Information
will go off on their own to make their own tracks. Thanks to fossil trackways re-
cently discovered in the United Arab Emirates which show a series of parallel and
overlapping tracks (group behavior) crossed by one trackway (a lone male), we
know elephants and their relatives have likely held these same behaviors minimally
for the past seven million years.
These behaviors also imply that local vegetation is normally worn down and
sediments compacted by groups of elephants, not individuals, and that once a path
has been cleared, it will be used repeatedly, perhaps by generations of elephants.
Elephants also need plenty of water, so they try to stay near rivers or ponds, which
they often enter and exit to drink or bathe. These habits mean they wear down
banks, form wide divots on those banks, and muck up water-body bottoms, espe-
ciallyiftheystartwallowing.Elephanttrailscanalsoformdepressionsdeepenough
for water to flow along them, creating canals that connect previously isolated rivers
or ponds. Trails on riverbanks similarly allow easier passage for floodwaters to cut
throughleveesandpouroutontofloodplains,depositingsedimentinwhatarecalled
crevasse splays
.
Modern hippopotamuses (hippos), despite being smaller than elephants—with
adults weighing in at 2.5 to 4 tons—have an even larger impact on their aquatic en-
vironments, which is where they spend most of their time. In a study by geologist
DanielDeoCampopublishedin2002,hedocumentedhowhipposinTanzaniamade
a 30 m (100 ft) wide and 2 m (6.6 ft) deep muddy wallow pond, which connec-
ted to 1 to 5 m (3.3-16 ft) wide trails that imparted radiating and branching pat-
terns onto the surrounding landscape. Hippos made these trails by frequently mov-
ing into and out of the wallow pond to feed on nearby vegetation; their activities,
combined with their bulks, compressed and otherwise altered sediments. Most im-
portant, hippo trails actually changed the direction for water flow in the area, in
which channels followed the trails, a type of channel abandonment called an
avul-
sion
. This channelization via hippo traces, in which their trails eventually turn into
new river channels, is also well documented in the Okavango Delta of Botswana.
