I am interested in prehistoric Amazonia, Geoarchaeology, Remote Sensing, Paleo-ecology, Paleo-rivers and Paleo-soils. Have a look at my blog to get a better idea of what I do http://umba-moxos.blogspot.com/ Phone: +41 (0)31 631 8578 Address: Geographisches Institut der Universität Bern (GIUB) Hallerstrasse 12 CH-3012 Bern Office 411
This paper investigates the dynamics of logjam-induced floods and alluvial deposition in the Boli... more 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 (1984–2016) 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.
ABSTRACT The Río Grande (Guapay) catchment in the Central Andes of Eastern Bolivia constitutes th... more ABSTRACT The Río Grande (Guapay) catchment in the Central Andes of Eastern Bolivia constitutes the southernmost extension of the Amazonian drainage system and feeds one of the largest megafans in South America. Today, the Río Grande flows into the Río Mamoré, marking the transition from a distributive to tributive channel network. A rich record of preserved paleochannels has been in a variety of remote sensing imagery, and reflects the dynamic history of large-scale channel shifts across the >55.000 km2 large Grande system. However, virtually no chronological information exists with regard to the temporal and spatial scales of these megafan processes, precluding the reconstruction of late Quaternary and Holocene megafan dynamics, and significantly limiting our insight into potential mechanisms and controls on megafan evolution. Here, we (i) present the results of an in-depth geomorphic study of megafan geomorphology, and (ii) provide first stratigraphic and chronological data from four different transects across the Río Grande and Mamoré megafans between ~19°S and ~13°S. Our study shows comparatively rapid and impulsive channel shifts along the proximal Río Grande megafan during the mid- to late Holocene, establishing the connection between the Grande and the Mamoré system along the distal megafan, and thus representing a major reorganization in the drainage network of the Bolivian Amazon basin. The corresponding increase in discharge and sediment load is readily expressed in downstream paleochannel and channel geometry, and may have triggered a late Holocene avulsion of the Río Mamoré meander-belt observed in our data. In combination with the available information from regional paleoclimate proxy records, these results point to climate and environmental change as a dominant control on megafan dynamics during the Holocene, and ultimately contribute to an improved understanding of megafan processes and their relevance for landscape evolution on all Quaternary timescales.
ABSTRACT Since the beginning of the 1960s, research in the Amazon has revealed that in Pre-Columb... more ABSTRACT Since the beginning of the 1960s, research in the Amazon has revealed that in Pre-Columbian times, landscapes that were viewed as challenging living environments were nevertheless altered in several ways. Raised fields agriculture is one of the most impressive phenomena that can be found in South-eastern Amazonia. Pre-Columbian raised fields are earth platforms of differing shape and dimension that are elevated above the landscape's natural surface. The Llanos de Moxos, situated in the Bolivian Lowlands is one of the areas with the highest density of raised fields. In spite of the high interest in raised field agriculture, very few field-based investigations have been performed. As a result, there remains little explanation as to how they were constructed, managed or for what time frame they were in use. Recently, more detailed investigations have been performed on raised fields located in the indigenous community of Bermeo, in the vicinity of San Ignacio de Moxos. Combined data from fieldwork and laboratory analysis including particle size distribution, thin section micromorphology and radiocarbon analyses as well as optically stimulated luminescence analysis has given an insight into the history of their construction. Applied to the Bolivian Lowlands, the current study provides for the first time data showing aspects of the Pre-Columbian management of the raised fields, and a chronological sequence of utilization and abandonment of these fields. Radiocarbon dating has shown that the raised fields had been in use since as early as 900 AD. Two distinct paleosols identified in the field sequence point to the existence of two separate prolonged soil formation periods. The paleosols are characterized by initial stages of Bt-horizons. Each soil sequence indicates therefore a particular stable period of the field during which no new earth was heaped up. This suggests that contrary to the well supported theory that raised fields were managed through continuous accumulation of sediments transported from the canal to the field, the raised fields were more likely built during large, single construction events.
ABSTRACT The presence of hundreds of rectangular and oriented lakes is one of the most striking c... more ABSTRACT The presence of hundreds of rectangular and oriented lakes is one of the most striking characteristics of the Llanos de Moxos (LM) landscape, a seasonally flooded savannah which constitutes the Central Andean foreland basin. Besides being rectangular and oriented at about 45 degrees north, these lakes are characterized by being very shallow and having a flat bottom. Many different mechanisms have been proposed for their formation including subsidence resulting from the propagation of bedrock faults through the foreland sediments, scouring caused by large-scale flooding, paleo deflation combined with wind/wave action and human agency. This wide range of hypothesis responds to a lack of field data and to the very limited number of studies on the matter. Nevertheless, amid this diversity of hypothesis, the most commonly accepted cause of lake formation to date has been tectonics. Thanks to our recent discovery of a paleosol below mid-Holocene fluvial sediments in the south-eastern LM, where several lakes are found, it is now possible to test the tectonic hypothesis. If lakes were formed by local subsidence induced by bedrock faults, we should find the paleosol at a greater depth below the lake than in the area surrounding it. Stratigraphic profiles from transects that cut across the borders of three lakes show otherwise: the depth of the paleosol is the same. Hence, tectonics, as the mechanism behind the formation of the lakes, can be ruled out. The origin of the Moxos rectangular and oriented lakes is still very much unresolved.
ABSTRACT The Llanos de Moxos (LM), in the Bolivian lowlands, is a seasonally flooded savannah whi... more ABSTRACT The Llanos de Moxos (LM), in the Bolivian lowlands, is a seasonally flooded savannah which has been inhabited since the beginning of the Holocene. Early Holocene archaeological sites, mostly shell middens, are nowadays hidden under forest islands: patches of forest surrounded by savannah. Despite their similar aspect, these archaeological sites are located in very different geomorphological and stratigraphic settings. Preliminary results of geo-archaeological research on two early-Holocene sites and their surroundings will be presented. The data suggests that the early Holocene landscape of the LM was significantly different from what we see nowadays. One of the sites, associated with an early to mid-Holocene paleosol, has been almost totally buried by fluvial sediments and only its topmost 30-40 cm has remained above the alluvium that forms the current savannah. The second site, currently outcropping in the middle of a flat swamp, was actually located on a sandy fluvial levee and subsequently flooded and partially buried by peat-like sediments. The events that lead to the burial of these sites, and probably caused the abandonment of the area, are still not completely understood. Linking together paleo-ecological reconstructions and archaeology, this research hopes to shed some light on the large scale environmental changes that took place in south-western Amazonia during the Holocene, the nature of human-environment interactions at the time and the potential value of these sites as paleo-environmental proxies.
ABSTRACT Recent archaeological research suggests that some parts of the Amazon Basin were signifi... more ABSTRACT Recent archaeological research suggests that some parts of the Amazon Basin were significantly modified by pre-Columbian populations. One of the most impressive examples of such transformations is the raised fields of south-western Amazonia, in the Llanos de Moxos in the Bolivian Lowlands. Despite a growing interest in raised field agriculture, due to the important role it seems to have played in the development of pre-Columbian complex societies, very few field-based investigations have been performed in the Amazon Basin. As a result, there is limited knowledge of how these fields were constructed, managed and within which time-frame they were in use. This study provides a new interpretation of how pre-Columbian raised fields were managed and a chronological sequence of their utilisation and eventual abandonment. Fieldwork was carried out in the indigenous community of Bermeo, in the vicinity of San Ignacio de Moxos, where some of the best preserved fields in the Llanos Moxos are found. Magnetic susceptibility and the geochemistry of the sediments, combined with radiocarbon and optically stimulated luminescence dating, show that the raised fields were in intermittent use since as early as AD 570–770. The original surface on which the fields were built and distinct periods of construction and use have been identified. The data suggests that raised fields were built during a few separate construction events, probably linked to periods of more frequent and severe floods. The study challenges the most widely accepted theory that suggests that pre-Columbians were able to cultivate these fields on a continuous basis by transferring nutrient-rich sediments from the canals to the fields. We conclude that pre-Columbians built raised fields to overcome periods of increased flooding, with the main objective of improving drainage.
Quantitative measures of polygon shapes and orientation are important elements of geospatial anal... more Quantitative measures of polygon shapes and orientation are important elements of geospatial analysis. These kinds of measures are particularly valuable in the case of lakes, where shape and orientation patterns can help identifying the geomorphological agents behind lake formation and evolution. However, the lack of built-in tools in commercial geographic information system (GIS) software packages designed for this kind of analysis has meant that many researchers often must rely on tools and workarounds that are not always accurate. Here, an easy-to-use method to measure rectangularity R, ellipticity E, and orientation O is developed. In addition, a new rectangularity vs. ellipticity index, REi, is defined. Following a step-by-step process, it is shown how these measures and index can be easily calculated using a combination of GIS built-in functions. The identification of shapes and estimation of orientations performed by this method is applied to the case study of the geometric and oriented lakes of the Llanos de Moxos, in the Bolivian Amazon, where shape and orientation have been the two most important elements studied to infer possible formation mechanisms. It is shown that, thanks to these new indexes, shape and orientation patterns are unveiled, which would have been hard to identify otherwise.
Abstract. In the present paper we explore to what degree soil properties might have influenced pr... more Abstract. In the present paper we explore to what degree soil properties might have influenced pre-Columbian settlement patterns in the Monumental Mounds Region (MMR) of the Llanos de Moxos (LM), Bolivian Amazon. Monumental mounds are pre-Hispanic earth buildings and were preferentially built on mid to late Holocene paleo levees of the Grande River (here denominated PR1), while levees of older paleorivers (PR0) were only sparsely occupied. We dug two transects across PR0 and PR1 levee-backswamp catenas and analysed them for grain size, pH, CEC and Corg. Our data show that PR1 soils, where the density of mounds is higher, have far greater agricultural potential than PR0 soils, which are affected by aluminium toxicity in the backswamps and by high levels of exchangeable sodium in the levees. This study provides new data on the soil properties of the south-eastern Bolivian Amazon and reinforces the thesis that environmental constraints and opportunities exerted an important role on pre-Columbian occupation patterns and the population density reached in the Bolivian Amazon.
The reconstruction of past environmental and historical events is much needed in Amazonia, a regi... more The reconstruction of past environmental and historical events is much needed in Amazonia, a region at the centre of heated debates about the extent of pre-Columbian human disturbance of the natural ecosystems. Important aspects of this debate are to establish to what extent the rise of social complexity was influenced by the local geo-ecology; and what productive strategies were adopted in order to sustain these societies. The Llanos de Moxos (LM), in the Bolivian Amazon, is a vast floodplain made up of a variety of geo-ecological sub regions that host many different types of pre-Columbian earthworks. Therefore, it offers an excellent opportunity to compare different kinds of archaeological landscapes and their relationship to different pre-Columbian cultures and environmental settings. This paper analyses the links between pre-Columbian earthworks and the local geo-ecology in two regions of the LM: 1) the platform field region (PFR) in the north of Santa Ana de Yacuma, where the highest concentration of raised fields has been documented, and 2) the monumental mounds region (MMR) south and east of Trinidad, where >100 pre-Columbian monumental mounds are found. The study draws from remote sensing and GIS analysis, field work in the Bolivian lowlands, and laboratory analysis. Differences in the way people transformed the landscape in the PFR and MMR seem to respond to differences in the local geo-ecology of the two sites. The results also suggest that environmental conditions exerted an important, though not exclusive, control over the levels of social complexity that were reached in different areas of the LM.
This paper investigates the dynamics of logjam-induced floods and alluvial deposition in the Boli... more 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 (1984–2016) 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.
ABSTRACT The Río Grande (Guapay) catchment in the Central Andes of Eastern Bolivia constitutes th... more ABSTRACT The Río Grande (Guapay) catchment in the Central Andes of Eastern Bolivia constitutes the southernmost extension of the Amazonian drainage system and feeds one of the largest megafans in South America. Today, the Río Grande flows into the Río Mamoré, marking the transition from a distributive to tributive channel network. A rich record of preserved paleochannels has been in a variety of remote sensing imagery, and reflects the dynamic history of large-scale channel shifts across the >55.000 km2 large Grande system. However, virtually no chronological information exists with regard to the temporal and spatial scales of these megafan processes, precluding the reconstruction of late Quaternary and Holocene megafan dynamics, and significantly limiting our insight into potential mechanisms and controls on megafan evolution. Here, we (i) present the results of an in-depth geomorphic study of megafan geomorphology, and (ii) provide first stratigraphic and chronological data from four different transects across the Río Grande and Mamoré megafans between ~19°S and ~13°S. Our study shows comparatively rapid and impulsive channel shifts along the proximal Río Grande megafan during the mid- to late Holocene, establishing the connection between the Grande and the Mamoré system along the distal megafan, and thus representing a major reorganization in the drainage network of the Bolivian Amazon basin. The corresponding increase in discharge and sediment load is readily expressed in downstream paleochannel and channel geometry, and may have triggered a late Holocene avulsion of the Río Mamoré meander-belt observed in our data. In combination with the available information from regional paleoclimate proxy records, these results point to climate and environmental change as a dominant control on megafan dynamics during the Holocene, and ultimately contribute to an improved understanding of megafan processes and their relevance for landscape evolution on all Quaternary timescales.
ABSTRACT Since the beginning of the 1960s, research in the Amazon has revealed that in Pre-Columb... more ABSTRACT Since the beginning of the 1960s, research in the Amazon has revealed that in Pre-Columbian times, landscapes that were viewed as challenging living environments were nevertheless altered in several ways. Raised fields agriculture is one of the most impressive phenomena that can be found in South-eastern Amazonia. Pre-Columbian raised fields are earth platforms of differing shape and dimension that are elevated above the landscape's natural surface. The Llanos de Moxos, situated in the Bolivian Lowlands is one of the areas with the highest density of raised fields. In spite of the high interest in raised field agriculture, very few field-based investigations have been performed. As a result, there remains little explanation as to how they were constructed, managed or for what time frame they were in use. Recently, more detailed investigations have been performed on raised fields located in the indigenous community of Bermeo, in the vicinity of San Ignacio de Moxos. Combined data from fieldwork and laboratory analysis including particle size distribution, thin section micromorphology and radiocarbon analyses as well as optically stimulated luminescence analysis has given an insight into the history of their construction. Applied to the Bolivian Lowlands, the current study provides for the first time data showing aspects of the Pre-Columbian management of the raised fields, and a chronological sequence of utilization and abandonment of these fields. Radiocarbon dating has shown that the raised fields had been in use since as early as 900 AD. Two distinct paleosols identified in the field sequence point to the existence of two separate prolonged soil formation periods. The paleosols are characterized by initial stages of Bt-horizons. Each soil sequence indicates therefore a particular stable period of the field during which no new earth was heaped up. This suggests that contrary to the well supported theory that raised fields were managed through continuous accumulation of sediments transported from the canal to the field, the raised fields were more likely built during large, single construction events.
ABSTRACT The presence of hundreds of rectangular and oriented lakes is one of the most striking c... more ABSTRACT The presence of hundreds of rectangular and oriented lakes is one of the most striking characteristics of the Llanos de Moxos (LM) landscape, a seasonally flooded savannah which constitutes the Central Andean foreland basin. Besides being rectangular and oriented at about 45 degrees north, these lakes are characterized by being very shallow and having a flat bottom. Many different mechanisms have been proposed for their formation including subsidence resulting from the propagation of bedrock faults through the foreland sediments, scouring caused by large-scale flooding, paleo deflation combined with wind/wave action and human agency. This wide range of hypothesis responds to a lack of field data and to the very limited number of studies on the matter. Nevertheless, amid this diversity of hypothesis, the most commonly accepted cause of lake formation to date has been tectonics. Thanks to our recent discovery of a paleosol below mid-Holocene fluvial sediments in the south-eastern LM, where several lakes are found, it is now possible to test the tectonic hypothesis. If lakes were formed by local subsidence induced by bedrock faults, we should find the paleosol at a greater depth below the lake than in the area surrounding it. Stratigraphic profiles from transects that cut across the borders of three lakes show otherwise: the depth of the paleosol is the same. Hence, tectonics, as the mechanism behind the formation of the lakes, can be ruled out. The origin of the Moxos rectangular and oriented lakes is still very much unresolved.
ABSTRACT The Llanos de Moxos (LM), in the Bolivian lowlands, is a seasonally flooded savannah whi... more ABSTRACT The Llanos de Moxos (LM), in the Bolivian lowlands, is a seasonally flooded savannah which has been inhabited since the beginning of the Holocene. Early Holocene archaeological sites, mostly shell middens, are nowadays hidden under forest islands: patches of forest surrounded by savannah. Despite their similar aspect, these archaeological sites are located in very different geomorphological and stratigraphic settings. Preliminary results of geo-archaeological research on two early-Holocene sites and their surroundings will be presented. The data suggests that the early Holocene landscape of the LM was significantly different from what we see nowadays. One of the sites, associated with an early to mid-Holocene paleosol, has been almost totally buried by fluvial sediments and only its topmost 30-40 cm has remained above the alluvium that forms the current savannah. The second site, currently outcropping in the middle of a flat swamp, was actually located on a sandy fluvial levee and subsequently flooded and partially buried by peat-like sediments. The events that lead to the burial of these sites, and probably caused the abandonment of the area, are still not completely understood. Linking together paleo-ecological reconstructions and archaeology, this research hopes to shed some light on the large scale environmental changes that took place in south-western Amazonia during the Holocene, the nature of human-environment interactions at the time and the potential value of these sites as paleo-environmental proxies.
ABSTRACT Recent archaeological research suggests that some parts of the Amazon Basin were signifi... more ABSTRACT Recent archaeological research suggests that some parts of the Amazon Basin were significantly modified by pre-Columbian populations. One of the most impressive examples of such transformations is the raised fields of south-western Amazonia, in the Llanos de Moxos in the Bolivian Lowlands. Despite a growing interest in raised field agriculture, due to the important role it seems to have played in the development of pre-Columbian complex societies, very few field-based investigations have been performed in the Amazon Basin. As a result, there is limited knowledge of how these fields were constructed, managed and within which time-frame they were in use. This study provides a new interpretation of how pre-Columbian raised fields were managed and a chronological sequence of their utilisation and eventual abandonment. Fieldwork was carried out in the indigenous community of Bermeo, in the vicinity of San Ignacio de Moxos, where some of the best preserved fields in the Llanos Moxos are found. Magnetic susceptibility and the geochemistry of the sediments, combined with radiocarbon and optically stimulated luminescence dating, show that the raised fields were in intermittent use since as early as AD 570–770. The original surface on which the fields were built and distinct periods of construction and use have been identified. The data suggests that raised fields were built during a few separate construction events, probably linked to periods of more frequent and severe floods. The study challenges the most widely accepted theory that suggests that pre-Columbians were able to cultivate these fields on a continuous basis by transferring nutrient-rich sediments from the canals to the fields. We conclude that pre-Columbians built raised fields to overcome periods of increased flooding, with the main objective of improving drainage.
Quantitative measures of polygon shapes and orientation are important elements of geospatial anal... more Quantitative measures of polygon shapes and orientation are important elements of geospatial analysis. These kinds of measures are particularly valuable in the case of lakes, where shape and orientation patterns can help identifying the geomorphological agents behind lake formation and evolution. However, the lack of built-in tools in commercial geographic information system (GIS) software packages designed for this kind of analysis has meant that many researchers often must rely on tools and workarounds that are not always accurate. Here, an easy-to-use method to measure rectangularity R, ellipticity E, and orientation O is developed. In addition, a new rectangularity vs. ellipticity index, REi, is defined. Following a step-by-step process, it is shown how these measures and index can be easily calculated using a combination of GIS built-in functions. The identification of shapes and estimation of orientations performed by this method is applied to the case study of the geometric and oriented lakes of the Llanos de Moxos, in the Bolivian Amazon, where shape and orientation have been the two most important elements studied to infer possible formation mechanisms. It is shown that, thanks to these new indexes, shape and orientation patterns are unveiled, which would have been hard to identify otherwise.
Abstract. In the present paper we explore to what degree soil properties might have influenced pr... more Abstract. In the present paper we explore to what degree soil properties might have influenced pre-Columbian settlement patterns in the Monumental Mounds Region (MMR) of the Llanos de Moxos (LM), Bolivian Amazon. Monumental mounds are pre-Hispanic earth buildings and were preferentially built on mid to late Holocene paleo levees of the Grande River (here denominated PR1), while levees of older paleorivers (PR0) were only sparsely occupied. We dug two transects across PR0 and PR1 levee-backswamp catenas and analysed them for grain size, pH, CEC and Corg. Our data show that PR1 soils, where the density of mounds is higher, have far greater agricultural potential than PR0 soils, which are affected by aluminium toxicity in the backswamps and by high levels of exchangeable sodium in the levees. This study provides new data on the soil properties of the south-eastern Bolivian Amazon and reinforces the thesis that environmental constraints and opportunities exerted an important role on pre-Columbian occupation patterns and the population density reached in the Bolivian Amazon.
The reconstruction of past environmental and historical events is much needed in Amazonia, a regi... more The reconstruction of past environmental and historical events is much needed in Amazonia, a region at the centre of heated debates about the extent of pre-Columbian human disturbance of the natural ecosystems. Important aspects of this debate are to establish to what extent the rise of social complexity was influenced by the local geo-ecology; and what productive strategies were adopted in order to sustain these societies. The Llanos de Moxos (LM), in the Bolivian Amazon, is a vast floodplain made up of a variety of geo-ecological sub regions that host many different types of pre-Columbian earthworks. Therefore, it offers an excellent opportunity to compare different kinds of archaeological landscapes and their relationship to different pre-Columbian cultures and environmental settings. This paper analyses the links between pre-Columbian earthworks and the local geo-ecology in two regions of the LM: 1) the platform field region (PFR) in the north of Santa Ana de Yacuma, where the highest concentration of raised fields has been documented, and 2) the monumental mounds region (MMR) south and east of Trinidad, where >100 pre-Columbian monumental mounds are found. The study draws from remote sensing and GIS analysis, field work in the Bolivian lowlands, and laboratory analysis. Differences in the way people transformed the landscape in the PFR and MMR seem to respond to differences in the local geo-ecology of the two sites. The results also suggest that environmental conditions exerted an important, though not exclusive, control over the levels of social complexity that were reached in different areas of the LM.
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Papers by Umberto Lombardo