Neotectonics, flooding patterns and landscape evolution in southern Amazonia

Lombardo, Umberto

doi:10.5194/esurf-2-493-2014

Cited by 27 publications

(39 citation statements)

References 69 publications

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“…The Beni and the Mamoré are characterized by high sedimentary loads, high meandering rates, and increasing discharge downstream (Aalto et al, 2003;Constantine et al, 2014;Guyot et al, 1996). They do not form logjams and they undergo avulsions on a millennial scale, mostly driven by neotectonic events and/or changes in climate (Dumont and Fournier, 1994;Lombardo, 2014;Plotzki et al, 2013). In contrast, their smaller tributaries often show downstream decreases in discharge, which is accompanied by the frequent formation of crevasses that often evolve into complete river avulsions (Lombardo, 2016).…”

Section: Discussionmentioning

confidence: 99%

“…They have very small mountain catchments; hence they enter the alluvial plains when they are still not very wide. Due to uplift events that have occurred north of the study area (Lombardo, 2014), the region is also extremely flat and the rivers have a relatively low transport capacity and a propensity toward river channel siltation (Lombardo, 2016). All these conditions contribute to the formation of channel-spanning logjams.…”

Section: Discussionmentioning

confidence: 99%

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River logjams cause frequent large-scale forest die-off events in southwestern Amazonia

Lombardo

2017

Earth Syst. Dynam.

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Abstract. This paper investigates the dynamics of logjam-induced floods and alluvial deposition in the Bolivian Amazon and the effects these have on forest disturbance and recovery cycles. It expands on previous work by Gullison et al. (1996) who reported a case of catastrophic floods triggered by logjams in the Chimane Forest in the Bolivian Amazon. No further studies have followed up on this observation and no research has been published on the effects of large wood in tropical lowland rivers. The study is based on the analysis of a time series of Landsat imagery and field evidence. Results show that logjam-induced floods are a major driver of forest disturbance along the Andean piedmont in the Bolivian Amazon. New logjams form on an almost yearly basis, always further upriver, until an avulsion takes place. Logjam-induced floods are characterized here by the sudden deposition of a thick sand layer and the death of forest in a V-shaped area. The Bolivian Amazon offers a unique opportunity for further research on how large wood affects river behavior in lowland tropical settings and how large and frequent forest disturbance events resulting from river logjams affect forest biodiversity and community successions.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

River logjams cause frequent large-scale forest die-off events in southwestern Amazonia

Lombardo

2017

Earth Syst. Dynam.

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“…Several paleocourses of the Río Beni have been identified, these seem to be the result of avulsions caused by a fault located a few kilometers from the Andes (Dumont and Fournier, 1994). The Mamoré avulsed during the mid-to-late Holocene (Plotzki et al, 2013) and occupied one of the Río Beni paleocurses (Lombardo, 2014). Stratigraphic cores performed across the alluvial plain have shown that, since the mid-Holocene, distributary fluvial systems formed by the Mamoré's tributaries (Fig.…”

Section: Study Areamentioning

confidence: 99%

“…Conclusions drawn from these studies of large Amazon rivers cannot be extrapolated to small rivers, because they differ in important aspects (Ashworth and Lewin, 2012). In the SAFB, the patterns of paleo channels show that it is not the large Río Mamoré but rather its tributaries that have deposited most of the sediments that form the modern alluvial plains (Lombardo et al, 2012;Lombardo, 2014;Hanagarth, 1993). Hence, it is important to further our understanding of the behaviour of these tributaries and the mechanisms controlling alluvial plain sediment accumulation.…”

Section: U Lombardo: Alluvial Plain Dynamics In the Southern Amazonimentioning

confidence: 99%

“…Stratigraphic cores performed across the alluvial plain have shown that, since the mid-Holocene, distributary fluvial systems formed by the Mamoré's tributaries (Fig. 1) have deposited thick layers of sediments over the southern and central part of the LM (Lombardo, 2014;Plotzki et al, 2015). This region hosts one of the most important collections of pre-Columbian earthworks in Amazonia, including monumental mounds, raised fields, ring ditches, fish weirs, canals and causeways (Lombardo et al, 2011;Prümers and Jaimes Betancourt, 2014).…”

Section: Study Areamentioning

confidence: 99%

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Alluvial plain dynamics in the southern Amazonian foreland basin

Lombardo¹

2016

Earth Syst. Dynam.

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Abstract. 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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Unfolding long‐term Late Pleistocene–Holocene disturbances of forest communities in the southwestern Amazonian lowlands

et al. 2018

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Linking the distribution of plant species to geology has generally been biased by the oversimplification of landscape evolution and the lack of understanding of complex geological processes. The Amazonian lowlands have forests in different successional stages, and a growing perception is that such heterogeneity results from long-term environmental changes. This hypothesis is investigated by designing an analytical model based on past and present-day vegetation and successions of the plant communities, combined with an advanced understanding of geological history. An area of southwestern Amazonia was selected for floristic inventories, and we interpreted the paleovegetation based on C/N and d 13 C analyses of sedimentary organic matter. These data were examined in the context of the geological evolution on the basis of new sedimentological and chronological data. The topographically high Late Pleistocene deposits had continuous and highly diversified late-successional terra firme forests as well as local fluvial paleolandforms of younger ages with less diversified campinarana forests. Late Pleistocene-Holocene terrains in intermediate elevations had terra firme forests, but shorter trees with lower basal areas and ecotonal forests appeared near the confines of the forest-savanna, while Holocene deposits recorded only seasonally flooded varzea forests. Several deposits of Late Pleistocene and Late Pleistocene-Holocene age recorded an expansion of C 4 terrestrial plants before the establishment of the forest from~20,000 cal yr BP to 7578 cal yr BP, which is not related to past arid episodes. We recorded forests with onsets at 6130-3533 cal yr BP, 3402-2800 cal yr BP, and 1624-964 cal yr BP to terra firme, varzea, and ecotonal forests, respectively. However, not all forests have reached maturity stages due to their location on terrains with a diverse history of terrace downcutting and deposition, which had a direct impact on local hydrology with the interaction of topographic gradients. The hydrology of the study area was also controlled by the distance from the main river valley. Capturing long-term disturbances over this region of still pristine forests may help elucidate the potential mechanisms that also determine trends in tree growth and forest diversity in other Neotropical regions.

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Neotectonics, flooding patterns and landscape evolution in southern Amazonia

Cited by 27 publications

References 69 publications

River logjams cause frequent large-scale forest die-off events in southwestern Amazonia

River logjams cause frequent large-scale forest die-off events in southwestern Amazonia

Alluvial plain dynamics in the southern Amazonian foreland basin

Unfolding long‐term Late Pleistocene–Holocene disturbances of forest communities in the southwestern Amazonian lowlands

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