Alluvial plain dynamics in the southern Amazonian foreland basin
Alluvial plains are formed with sediments that rivers deposit on the adjacent flood-basin, mainly through crevasse splays and avulsions. These result from a combination of processes, some of which push the river towards the crevasse threshold, while others act as triggers. Based on the floodplain se...
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2016-05-01
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| Series: | Earth System Dynamics |
| Online Access: | http://www.earth-syst-dynam.net/7/453/2016/esd-7-453-2016.pdf |
| Summary: | Alluvial plains are formed with sediments that rivers deposit on the adjacent
flood-basin, mainly through crevasse splays and avulsions. These result from
a combination of processes, some of which push the river towards the crevasse
threshold, while others act as triggers. Based on the floodplain
sedimentation patterns of large rivers in the southern Amazonian foreland
basin, it has been suggested that alluvial plain sediment accumulation is
primarily the result of river crevasse splays and sheet sands triggered by
above-normal precipitation events due to La Niña. However, more than
90 % of the Amazonian river network is made of small rivers and it is
unknown whether small river floodplain sedimentation is influenced by the
ENSO cycle as well. Using Landsat images from 1984 to 2014, here I analyse
the behaviour of all 12 tributaries of the Río Mamoré with a
catchment in the Andes. I show that these are very active rivers and that the
frequency of crevasses is not linked to ENSO activity. The data suggest that
most of the sediments eroded from the Andes by the tributaries of the
Mamoré are deposited in the alluvial plains, before reaching the parent
river. The mid-to-late Holocene paleo-channels of these rivers are located
tens of kilometres further away from the Andes than the modern crevasses. I
conclude that the frequency of crevasses is controlled by intrabasinal
processes that act on a yearly to decadal timescale, while the average location
of the crevasses is controlled by climatic or neo-tectonic events that act on
a millennial scale. Finally, I discuss the implications of river dynamics on
rural livelihoods and biodiversity in the Llanos de Moxos, a seasonally
flooded savannah covering most of the southern Amazonian foreland basin and
the world's largest RAMSAR site. |
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| ISSN: | 2190-4979 2190-4987 |