Environmental Earth Sciences (2018) 77:222 https://doi.org/10.1007/s12665-018-7405-7

ORIGINAL ARTICLE

Terras caídas: Fluvial erosion or distinct phenomenon in the Amazon?

Iris Celeste Nascimento Bandeira1 · Amilcar Adamy2 · Elton Rodrigo Andretta3 · Raimundo Almir Costa da Conceição1 · Milena Marília Nogueira de Andrade4

Received: 22 September 2017 / Accepted: 6 March 2018 / Published online: 14 March 2018 © Springer-Verlag GmbH Germany, part of Springer Nature 2018

Abstract In the Basin, as in other hydrographic regions of and the world, fuvial erosion processes occur because of rivers dynamics. However, the lateral erosion that occurs on banks of Amazonian rivers, called terras caídas, typically is associated with gravitational movements and is mainly related to large landslides that can damage structures or kill people who live along these riverbanks. To better understand the erosive processes that occur in rivers of northern Brazil, espe- cially those located in the Amazon River Basin, this work aims to describe the terras caídas phenomenon and determine whether it is a distinct phenomenon of fuvial erosion processes. The investigation includes analysis of hydrometeorological data of the National Water Agency (ANA), information collected during feld expeditions, and mapping of geological and hydrological risk areas in the states of Amazonas, , Rondônia, Pará, and Amapá performed by the Geological Survey of Brazil—(CPRM) from 2011 to 2016. It is concluded that terras caídas is a distinct phenomenon in the Amazon rivers that is diferent from erosive processes in other Brazilian rivers, because it is associated not only with the lateral erosion, but also with mass movements of moderate and large extents, which cause landslips, undermining, creeps, and major landslides.

Keywords Brazilian rivers · Fallen soil · Fluvial risk · Riverbanks · River erosion

Introduction According to Amazonian riverside inhabitants, terras caídas is a term used to designate lateral erosion associated In the Brazilian Atlas of Natural Disaster (UFSC-CEPED with the undermining, landslide, landslip, and collapse pro- 2013), information is recorded on droughts, gales, hail- cesses that occur on these riverbanks. However, as described storms, mass movements, erosion, fash food, foods, and by Carvalho (2006), fuvial erosion alone as an abrasive pro- terras caídas in the Amazon region. Although this latter cess resulting from the chemical and mechanical action of terminology is not widely known in other , moving water in a channel is insufcient to explain the ero- it has previously been used in regional literature by Tricart sion that occurs in the Amazonian rivers. (1977), Sioli (1984), Guerra (1993), Junk (1997), Sternberg One of the frst publications on the subject of terras (1998), Carvalho (2006), Carvalho et al. (2009), Adamy caídas was presented by Figueiredo (1945 apud Carvalho (2010), Teixeira (2010), Labadessa (2011), Freitas and 2006), who, in an excursion along the Solimões River in Albuquerque (2012), and Oliveira Filho and Adamy (2015). 1940, observed this phenomenon from afar and published In the Amazon, the Geological Survey of Brazil (CPRM) has a historical record with a brief description: “Suddenly, used the terminology terras caídas for risk areas associated there is a rumbling that comes to our ears, as from far, far with fuvial erosion (CPRM 2016). away, it was like a formidable charge of explosive have been exploded, it is a fallen soil (terra caída).” Guerra (1993) defned terras caídas as referring to the “digging” done by * Iris Celeste Nascimento Bandeira the water of rivers in the Amazon region, which undermines [email protected] ravines severely. In some cases, people have reported seeing 1 Serviço Geológico do Brasil (CPRM), Belém, Brazil large pieces of land moving as if they were foating islands. Studies of fuvial erosion have applied morphometric 2 Serviço Geológico do Brasil (CPRM), , Brazil analysis of a basin at diferent scales (basin, basin sectors, 3 Serviço Geológico do Brasil (CPRM), , Brazil and sub-basin). The extensive use of geoprocessing tools 4 Universidade Federal Rural da Amazônia, Belém, Brazil allows a quantitative interpretation of the geomorphological

Vol.:(0123456789)1 3 222 Page 2 of 16 Environmental Earth Sciences (2018) 77:222 aspects and the relations with fuvial dynamics and charac- give support to urban planning studies, and minimize the teristics (Rai et al. 2017; Quiroga et al. 2017). Using remote risks associated with this process. sensing and applying several mapping algorithms, a frst understanding of fuvial dynamics is possible in ungauged or poorly gauged basins (Sreedevi et al. 2013). Due to the Methodology dimension of Amazon River Basins the radar-image process- ing present errors that should be carefully processed and Study area feld observations are needed to minimize an exaggeration in data due to canopy afecting (Valeriano and Rossetti 2008). This research was conducted mainly in the urban areas of Although studies have been conducted on this topic, many 69 municipalities in six states of northern Brazil (Fig. 1): questions remain that require further research. The morpho- one municipality (Macapá) in the state of Amapá, three metric parameters quantifcation itself would not provide municipalities (Ariquemes, Ji-Paraná, and Porto Velho) in the diferentiation of terras caídas and fuvial erosion. The the state of Rondônia, nine municipalities (Xapuri, Porto Amazon River Basin dimension add the challenge to pro- Acre, Cruzeiro do Sul, Rodrigues Alves, Porto Walter, Feijó, duce results from specifc quantitative approaches, such Marechal Thaumaturgo, Rio Branco, and Sena Madureira) as the role of soil moisture and pore pressure in erosional in the state of Acre, eleven municipalities (Cametá, Cur- process. And some sub-basins are poorly gauged or have ralinho, Maracanã, Marapanim, Pontas de Pedra, Porto de discontinuous data. Therefore, the objective of this work Moz, Prainha, Quatipuru, Santarém, Soure, and Salvaterra) is prior to describe and analyze whether the terras caídas in the state of Pará, and forty fve municipalities (Anamã, phenomenon is a type of fuvial erosion or a separate phe- , Barcelos, , Bejamin Constant, nomenon, in order to standardize studies, identify solutions, , , , ,

Fig. 1 Location map of the study area

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Careiro, , Codajás, Eirunepe, , Fonte Boa, Gua- erosion (terras caídas) in the Amazon (Pará, Amazonas, jará, Humaitá, , , Itacoatiara, , Acre, Amapá, and Rondônia). Juruá, Jutaí, Lábrea, , , Manicoré, In addition to these eforts, information from feld expedi- Maraã, Nhamundá, , Novo Aripuanã, tions performed by CPRM in December 2012 was utilized, , , Santo Antônio do Iça, São Paulo de Oli- with details on the lithology of marginal slopes, vegetation, vença, São Sebastião do Uatumã, Silves, , Tefé, and types of mass movements. Many sites were investigated , , Urucará, , and Amatura) in along the banks of the Solimões River in parts of Manaus, the state of Amazonas. Manacapuru, Anamã, and Beruri. In the feld investigations According to the National Water Agency (ANA), these performed in the city of Cametá on the Tocantins riverbank, municipalities are distributed around the Amazon River in the countryside of Porto de Moz, and on banks of the Basin, Tocantins–Araguaia River, and Atlantic northeast Amazon River located in Prainha and Santarém, with the hydrographic regions. These areas are considered to be inside boundaries of the state of Pará, the constituent lithology of the jurisdictional context of Legal Amazon that is under a the riverbanks, width of drainage, and the infuences of veg- priority for socioeconomic development in compliance with etation and humans were analyzed. Law n° 1.806/53, Art. 2° and Law n° 5.173/66, Art. 2°, with a The fuvial morphodynamic analysis was assessed using territory increase by Complementary Law n° 31, 11.10.1977, the Google Earth Satellite Imagery with images dated between Art. 45; provisory measure n° 2.157-5, 24.08.2001, Art. 2°; 1969 and 2016. For several locations in the Amazon region, and currently Complementary Law n° 124/2007, Art. 2°. this phenomenon was identifed and the purpose of this multi- temporal analysis verifed the fuvial dynamics. The polygons Methods delimitation of the riverbanks eroded area was calculated made using geoprocessing operational methods in a geographical The methods employed for this study included bibliographi- information system (GIS) environment. However, in this paper, cal research, secondary hydrometeorological data collection, we presented Santarém study areas as an example. analysis of geological and hydrological risk sectors gathered by CPRM (2016), critical analysis of the results from feld research expeditions organized by CPRM in 2012, and fu- vial morphodynamic analysis. Theoretical framework The bibliographical research included information about relevant mention of terras caídas in books, articles, annals of Fluvial erosion around the world congress, dissertations and theses. Once it is a term mainly used for Amazon process, the literature available is mainly in The largest rivers in the world can be compared in terms of Portuguese. The secondary hydrometeorological data were basin area, extent, form, fow, sediment discharge, climate, acquired from automatic stations located in the principal sources, and mouth location (Table 1). The Amazon River rivers (Acre, Juruá, Envira, Iaco, Jamari, Taraucá, Purus, is the largest river in the world in terms of basin area, extent, Solimões, Amazon, and Madeira) and available by ANA and sediment discharge. The erosion processes in this river (2017). These data area charts from the period between have been studied in geological terms (Latrubesse and Fran- 1968 and 2016 include fow rate, elevation, sedimentary zinelli 2002), and multitemporal analysis (Passos and Soares load, water depth, and rainfall. Microsoft Excel was used 2017) has been used to investigate the riverbank landslips for graphical representation. called terras caídas (Freitas and Albuquerque 2012). These The geological and hydrological risk sectors were erosion processes are extensive and are associated with obtained from the results of the Emergency Action to Very meandering channels, alluvial deposits, and/or Tertiary age High and High Risk Areas Delimitation to Floods and Mass deposits (Latrubesse and Franzinelli 2002) in a region with Movement Project performed by CPRM between 2011 and an equatorial humid climate. 2016. This mapping of risk areas was legally based on Law The Congo River in Africa is the second largest river on n° 12.608/12 Chapter IV Article 6°, which defnes national Earth in terms of discharge and basin area and is located in support for the states and the federal district, and described the same climatic zone as the Amazon River; however, it the mapping of municipalities in at-risk areas (Brazil 2012) does not have high fuctuations of water level. The develop- for the purpose of preventing and reducing social and eco- ment of connected channels in the foodplain of the Amazon nomic losses related to natural disasters. While priorities difers in that it has difuse contacts and the fow patterns were foods and mass movement’s hazards, it was needed are not as well defned as those of the Congo River (Jung to map fuvial erosion process in the Amazon Rivers once et al. 2010). this process also generate damages. However, the descrip- The rivers in North America with the highest rates of tion and classifcation of the process are defned as fuvial fuvial erosion are the Mississippi River and the Missouri

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Table 1 Features of major fuvial systems in the world. Data adapted from Milliman and Meade (1983) River Continent Basin area Extent (km) Average Sediment Form Climate Source Mouth ­(km2) fow ­(m3/s) discharge ­(103 t/year)

Amazon South 6150 6275 200,000 900,000 Meandering Equatorial Nevado Atlantic America and braided humid Mismi, Ocean Congo Africa 3820 4670 40,600 43,000 Interlaced Equatorial Vale do Rift Atlantic and mean- humid Mountains Ocean dering Brahmapu- Asia 1480 2700 30,790 1,670,000 Interlaced Subtropical Himalayas Gulf of tra-Jamuna humid and Bengala windy Mississippi North 3270 6260 18,390 210,000 Meandering Subtropical Itasca Lake Gulf of America Mexico Yangtze Asia 1940 4090 28,540 478,000 Meandering Temperate Tibetan East China Plateau Sea

River. Both have meandering channels and were artifcially percolation. Abrasion occurs when there is mechanical channelized in the 1980s to improve of navigability. Subse- friction between particles in the water and materials in the quently, several erosive processes were identifed, related to riverbanks and riverbeds, which causes wear and removal infltration, landslides, and erosion of the riverbanks of these of unconsolidated layers. Cavitation occurs in high-speed rivers and their tributaries (Alexander et al. 2012). This rivers, which produces variations in pressure on the channel phenomenon was named solos caídos (fallen soils) and was wall and facilitates erosion (Suguio and Bigarella 1990), but reported to be directly infuenced by the amount of rainfall, this process only occurs in channels with minimum speeds water infltration, and a non-cohesive unit (Freitas 2009). of approximately 12 m/s, equivalent to 43.2 km/h (Hjulstrom In Asia, the Yangtze River of China originates on the 1939). Tibetan Plateau and has a hydroelectric dam along its Scherer (2008) described how the main erosive processes course. Erosion in the coastal region is related to reduction in fuvial systems are associated with the dynamics of fu- of sediment discharge over time caused by damming of this vial channels, which can be classifed into two main types: river (Li et al. 2015). Also in Asia, the Brahmaputra River incision and lateral migration. Incisions can be allocyclic in Bangladesh fows through a lowland composed of Qua- or autocyclic. Allocyclic incision is related to phenomena ternary sediments and transports approximately 1.1 billion that occur over longer periods and may be associated with tons of sediment every year (Jung et al. 2010). According increasing discharge, climatic changes, or reduced slope to Uddin and Basak (2012), these lowlands contain largely stability (Schumm 1993). Autocyclic vertical incisions are unconsolidated material that is easily eroded when the fow associated with avulsion (abrupt breakdown of parts of the of the river increases. Such increases are caused by high land by violent natural processes) of fuvial channels aris- rainfall rates in this region, which are associated with excess ing from hydrodynamic and geomorphological processes wind and glaciers melting into the Brahmaputra River. The on the alluvial plain (Jones and Schumm 1999). Like the average erosion rate of the Brahmaputra River was 160 m/ volume and velocity of river fow, the quantity and types year between 1973 and 1992 and 72.5–80 km2/year from of sediments transported and the width, depth, and slope 1997 to 2008 (Das et al. 2014). of the channel are associated with topographic diference between the source and mouth, the roughness of bed bot- Fluvial erosion in Brazil tom, and vegetation cover presents on the banks and islands (Riccomini et al. 2000). According to Suguio and Bigarella (1990), fuvial erosion In contrast, lateral erosion occurs through lateral migra- is a process whereby material is removed from the bottom tion of the channel, which is associated with high river sinu- and banks of a channel through corrosion, abrasion, and osity (Scherer 2008). Suguio and Bigarella (1990) reported cavitation. Therefore, it depends on the type, texture, and that enlargement of edges occurs because of adverse weather spatial distribution of geological and geotechnical features conditions and resulting mass movements as far as the river (Rotta and Zuquette 2014). Corrosion is a process of electro- fows. chemical reaction of the water (with dissolved salts) and sur- Hjulstrom (1939), Cunha (1995), Press et al. (2006), faces of rocks and sediments that become saturated during and Novo (2008) have reported that erosion, transport, and

1 3 Environmental Earth Sciences (2018) 77:222 Page 5 of 16 222 fuvial deposition depend on the fow velocity (hydraulic power) and grain size of the eroded material. At low stream velocities and low sediment load condition, particles of all sizes settle along the foodplain (Press et al. 2006). As the fow velocity increases, larger particles can be eroded or deposited; and when the velocity is high, both large and small particles are eroded (Hjulstrom 1939). The flow velocity also infuences the erosion of external bank and the deposition in internal bank of channels in shape of meander (Press et al. 2006).

Fig. 3 Number of people at risk from the phenomenon of terras caí- Results and discussion das in Amazonia. Data set from the sectorization of risk project by CPRM in the states of Manaus, Acre, Rondônia, Amapá, and Pará, for the years 2011–2016 Characterization of terras caídas in Amazonia

In total, 236 risk areas have been identifed for terras caí- with great water capacity in the interior. This phenom- das along the riverbanks of the Amazon (Fig. 2), which enon occurs more frequently and with greater intensity, afect around 25,000 people (Fig. 3). Carvalho (2006) although not exclusively, in white-water rivers with large regarded terras caídas as a phenomenon particularly to the sedimentary loads (Carvalho 2006). Amazonian rivers, which produce large foodplain areas

Fig. 2 Risk areas for terras caídas in the Amazon region: 152 in the state of Amazonas, 42 in the state of Acre, 35 in the state of Pará, six in Rondônia, and one in the state of Amapá. Data set from the sectorization of risk project by CPRM, between the years 2011 and 2016

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The terras caídas phenomenon has particularities inherent rivers, geology and tectonic efect. There are also infuence in the morphological conditions of the extensive Amazonian of vegetation and anthropic factors, such as deforestation rivers, which are characterized by features of large gravita- of riverbanks, release of wastewater, and waves caused by tional mass movements, similar to those that occur in moun- boats, but these factors are less signifcant. tainous regions of Brazil. Thus, the terras caídas phenomenon is related to removal of material from the bottoms and banks Climate of rivers through abrasion and corrosion. It is also associated with the processes of undermining, sliding, and creep, which, The main climatic factors that influence erosion of river- in turn, have their own features. banks are related to heavy rainfall and strong winds. The Undermining can occur in two ways: when the river average annual precipitation in the Amazon is approxi- is completely full (maximum capacity) and/or when the mately 2205 mm, over 25% higher than the national aver- water level is rising or falling. During foods, undermin- age of 1761 mm (ANA 2009). Overall, the rainy season ing (Fig. 4a, b) is characterized by collapse and submer- in the Amazon region occurs from November to April or sion of extensive masses. Often, when these landmasses December through May, depending on the municipality are undermined, they are separated from the riverbank and (CPRM 2011). This precipitation is related to high super- are removed by the current and thus form foating islands. ficial hydric availability of 73,748 m3/s, approximately When the water level is rising or falling, that is, when the 80% of Brazil’s superficial availability (91,071 m3/s), river is not at its maximum food level, the river current and 10.5% of the Earth’s available freshwater (ANA removes more erodible material from the deepest portion 2015). of the river (generally below the level of trees roots), and The high average annual precipitation provides an amount the upper portion of the ravine collapses or falls because of of water that increases the sewage till 205.000 m3/s (ANA gravity (Fig. 4c, d). 2016). The volume of water that infltrates the soils during Sliding is associated with ruptures on marginal slopes rainy months and accumulates because of high permeability of the Amazonian rivers, the high declivity of which can and porosity makes the structures of the plains and terraces exceed 80° (Pereira and Andretta 2010) (Fig. 4e, f). The dif- heavier and predisposes them to mass movements (Rodri- ference is that in addition to gravity and rainwater, there is gues 2014). According to Carvalho (2006), disaggregation another factor responsible for the triggering process in these of material takes place more often during the largest rainfalls riverbanks: the hydrostatic pressure mentioned by Tricart and river foods, when there is increase of fow and hydraulic (1977) and Sternberg (1998), which is specifcally related pressure. to the river’s dry fow. However, the term “sliding” is little The wind acts as an erosive agent by producing high and known among the “ribeirinha” (riverside people) popula- intense waves, which are associated with currents causing tion, who uses more generic terms in the folk language as abrasion, and can trigger landfalls along the riverbanks. The fall, barriers falling, and land collapse. intensity and speed of wind present a relation with the width Another process observed in riverbanks is creep, which of rivers. Winds reach higher speeds in wider channels, can trigger possible undermining during the full fow of the which favors the incidence of stronger waves with greater river or slipping during dry fow. This process is character- destructive potential. ized by a displacement along a plane (cracks and steps) in a slope at a relatively steep incline, between 20° and 30°, associated with sandy clay material, and moves more slowly Fluvial hydrodynamics (Fig. 4g, h). Frequently, these processes are interrelated; in other words, erosion associated with mass movement can Most of the rivers in the Amazon River Basin, occur more slowly, like creep, in the same riverbank, and Tocantins–Araguaia Basin, and Atlantic northern basin if conditions change, sliding or undermining may be trig- exist in a geomorphological context where fuvial dynam- gered. In addition, when there are lithological diferences or ics are very active. In this study, 84% of the studied sites erosion at the base of the slope, the process of undermining were located at the portion of the river with a meandering may occur. pattern, 9% with a rectilinear pattern, and 7% were related and mainly associated with the concave bank, (75%) of the Likely triggers of the terras caídas process river and where 13% of erosions are in the convex bank, and in the Amazon 12% in the rectilinear bank (CPRM 2016). A study case in Santarém city located at the Amazon and Tapajós River con- For a terras caídas to occur, several factors must interact fuence shows a continuous process of erosion in riverbanks. together with very intense fuvial dynamics. These factors In the period of 47 years, an area of 17.8 km2 was eroded and include climate, fuvial hydrodynamics, sedimentary load 14.6 km2 was deposited (Fig. 5a–c).

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Fig. 4 a São Braz locality, Porto de Moz, Pará, where undermin- ing has occurred on the bank of the Amazon River and resulted in loss of over 500 m of loss land, caused by fooding in the Amazon River in August 2016. Courtesy of Defesa civil estadual do Pará (2016). b Schematic showing the under- mining process during the food. c Lateral erosion of the base of a slope along the , which indicates that fall- ing occurs from bottom to top and threatens the population of the Calama district. Courtesy of Defesa civil de Porto Velho (2013). d Schematic display- ing the undermining process during dry fow. e Formation and evolution of steps at the right bank of the Juruá River in the Porto Alegre community, Ipixuna-Amazonas municipal- ity. Courtesy of CPRM (2014). f Illustrative profle exhibiting the basic geomechanical model of sliding hazards in riverbanks (a) in the period of ebb, with water fow (b) post-rupture situation indicating fall of vegetation, irregularities on the ground, and cracks. g Slope with decliv- ity between 20° and 30°, and steps on the bank of the in the state of Amazonas. Photograph taken during the Expedition of Terras Caídas in 2012. h Schematic showing the creep model

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Fig. 5 a Satellite image from December 1969 and b Google Earth 47 years. c Changes in the banks of the Amazon River, indicating Image from September 2016 of the municipality Santarém-Pará, areas with accretion and erosion showing the river dynamics of the Amazon River in the period of

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Fig. 5 (continued)

Because water fow and sediment supply change over attributed the undermining of riverbanks to high amplitudes time, alluvial channels are continuously adjusting their of discharge fuctuations during food fow. It was reported form by means of depositional and erosive processes (Ste- that during dry fow, numerous semicircular holes appeared vaux and Latubresse 2017). These fuvial dynamics, which near the sandy clay alluvium. Still in the dry fow, some cause erosion and deposition, are controlled mainly by the authors observed that bank failures are likely to occur dur- fow (hydraulic action), thalweg position, depth, water level ing pore pressure drawdown following a high water level variation, geometry and sedimentary input of the river, as stage (Springer et al. 1985; Lawler et al. 1997). When the well as by the lithology of the bank and/or tectonic factors. bank material is still in or near a saturated condition and Based on analysis, the depth and fow of the Acre, Envira, the confning pressure of the river decreases, the saturated Iaco, Jamari, Juruá, Madeira, Tarauacá, Purus, and Solimões soil presents higher probability to mass movement process Rivers, are associated with terras caídas in 23 risk areas (Rinaldi et al. 2004). mapped by CPRM, and outfows are found to be greater dur- In the Amazon, food variance follows seasonal pat- ing food fow (Fig. 6). terns that do not necessarily accompany rainfall trends. The terras caídas phenomenon occurs preferentially in During the food season, the river height increases until it deeper portions of the river where the fow rate is higher, reaches a maximum peak, whereas during the dry phase, such as the waterfront of the city of Cametá in the state of water level and ebb tide quotas decrease, until they reach Pará (Fig. 7a, b). This fnding has been confrmed by Cunha a minimum. Depending on the river, food events occur (1995) and Novo (2008), who point out that the power of a between the months of December and May, January and river increases with the fow (discharge) and with the density June, or March and August, as indicated in Fig. 8. Dif- of the water. ferences between the maximum water level in food and Among hydrodynamic factors, water level variation is minimum water level in the dry season and ebb tide can another factor that may infuence the terras caídas phe- reach 12 m in height (Fig. 8). Among zones at risk to ter- nomenon. Tricart (1977) and Sternberg (1998) studied ras caídas in the study area, 45% yielded no information the genesis and types of fuvial beds in the Amazon and on whether the process would occur during the food or

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Fig. 6 Chart displaying the relationship between depth and fow in the full fow period and dry fow period at sites of rivers where risks of terras caídas were identifed. Flow rates were extracted from the ANA database (ANA 2017) for the period between 1968 and 2016

ebb phase, 38% indicated that erosive processes, sliding, However, the erosion of riverbanks is rarely the result of and undermining occurred during both phases, 16% indi- a single process, but rather from a combination of geologi- cated that sliding and collapse occurred during the ebb cal, neotectonic, climatic, geomorphological, and pedologi- phase, and one zone presented erosion that occurred only cal factors, and, to a lesser extent, human activity. Tricart in the food phase. (1977), Sternberg (1998) and Freitas (2009) reported that Freitas (2009) and Freitas and Albuquerque (2012) veri- erosion is caused by deepening of the riverbed during high fed that there is more erosion when the river is rising, which tides and sliding in low tides. Not only occurs deepening but was attributed to increasing hydraulic pressure associated also enlargement of the river occurs when the water level with heavy rainfalls infltration into the riverbanks sand, is high. As a consequence of lateral erosions, the material silt, and clay. Therefore, water, which is the main agent of slides when the water level is low and can subsequently be dynamics in a hydrographic system, exercises mechanical transported by the fow of the river when water level next strength as well as chemical activity. rises, as occurred in Brasileia in the state of Acre in 2015.

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and gravel from Quaternary age (CPRM 2004; Ferreira et al. 2007; Quadros and Rizzotto 2007; Vasquez et al. 2008). Therefore, the mechanical properties of a riverbank are related to its granulometric composition, resistance to erosion, and cohesiveness related to silt and clay content. According to Couper (2003), the high susceptibility to ero- sion by subaerial processes on river banks depends on high silt–clay contents. In the study area, it was verifed that fuvial erosion occurs preferentially in sandy sediments, sandy clay sedi- ments, sandy silt–clay sediments, silt–clay sediments, and expansive clays with little consolidated in alluvial plans, which can extend more than 50 km in width, when whole islands are transported by the water of the river. However, erosion was also observed in soils of older Tertiary units, with geotechnical characteristics that include greater resis- tivity than alluvium and typically contain intercalations of sandy and clayey sediments. This material sustains fuvial slopes with heights that vary between 20 cm and 25 m and declivities above 60°, which cause instability of the sedimentary body and make it susceptible to triggers of the erosion. The height of the slope has a smaller efect than the declivity. Moreover, it was verifed that this erosion occurs in the upper, mid- dle, and lower courses of rivers, which demonstrates that vertical erosion is associated with deepening the bottom of the river. Therefore, the landscape formation process relating neotectonic uplifting factors and fuvial erosion Fig. 7 a A wooden pier and a stone shed from the 1970s on the also relates to terras caídas spatial distribution. waterfront of the city of Cametá in the state of Pará. Photograph The tectonic for the entire Amazon region is infuenced available in http://luisp​eresc​ameta​.blogs​pot.com.br/p/museu​-de-fotos​ .html. b Note the advancement of erosion, which destroyed both the by neotectonics and the presence of dextral strike-slip wooden pier and the shed. Photograph taken by Iris Bandeira in 2013 faults in the E–W and NE–SW directions, thrusting in the NE–SW direction, and normal faults in the NW–SE (Costa et al. 1996) (Fig. 9a). This fault confguration generates Sedimentary load of rivers earthquakes with magnitudes between 2 and 5.2 on the Richter scale (Fig. 9b) and represents strain relief along In the Amazon region, rivers are designated as white water, preexisting reactivated faults or, less commonly, neofor- dark water or clear water, based on the concentration of sedi- med faults, which indicates tectonic control (Brazilian ments (water transparency/sedimentary load in suspension, Seismographic Network 2014). According to Igreja and bed load). According to Carvalho (2006) The terras caídas Catique (1997), this tectonic confguration contributes to process only occurs in white-water rivers. However, based the direction of the existing drainage network, as well as to on data from risk mapping performed by CPRM, fuvial the occurrence of erosive processes in riverbanks. erosion was observed for rivers with white, dark, and clear However, no analysis has yet been carried out to assess water; 79% of fuvial erosion was caused by white water, how and which magnitude of an earthquake could trig- 13% by dark water, and 7% by clear water, with no informa- ger sliding or an undermining of the riverbank. Around tion available for the remaining 1%. 13 risk sectors of terras caídas are nearby epicenter with magnitude 3 on Richter scale. Carvalho et al. (2009) in Geology a previous study case observed the recurrent subsidence process in 1973, 1994, 1997, and 2007 in Parintins (Ama- The geology corresponds to mainly alluvial sediments zonas). During the subsidence process the riverbank col- deposit along the Amazon River plains. This main forma- lapsed and generate waves between 6 and 8 m in height. tion are represented by subaqueous sand and conglomerate These waves along with hydrostatic pressure and the bars, foodplain sediments varying from sand, silt, clay,

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Fig. 8 Charts showing curves in water level and precipitation at loca- the city of Manacapuru, M; the Purus River in the city of Canutama, tions along the Juruá River in the city of Porto alter, AC; the Acre AM; the Madeira River in the city of Humaitá, AM; and the Amazon River in the municipality of Rio Branco, AC; the Solimões River in River in the city of Santarém. Data set from ANA 2017) largely unconsolidated sediments contributed to collapse Infuence of vegetation of the riverbank, which sank by 76.7 m and resulted in one fatality . Other variables that contribute to increasing resistance to erosion are the vegetal cover of riverbanks and the amount

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Fig. 9 a Neotectonic setting of the Amazon region, showing major faults according to Costa et al. (1996). b Map of epicenter distribution in the Amazon region. Courtesy of Brazilian Seismographic Network (2014)

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Table 2 Factors that infuence fuvial erosion and the terras caídas phenomenon Infuential factors Fluvial erosion Terras caídas References

1. Predominant climate All climates Equatorial humid climate Filizola et al. (2002) 2. Do winds infuence the erosion? Without reference Yes Carvalho (2006) 3. Do corrosion and/or abrasion Yes Yes Suguio and Bigarella (1990) and occur? Riccomini et al. (2000) 4. Lateral/vertical erosion Yes Yes Novo (2008) and Scherer (2008) 5. Fluvial hydrodynamics (laminar Yes Yes Christofoletti (1980), Novo (2008), or turbulent fow) Cunha (1995), Sternberg (1998) and Suguio and Bigarella (1990) 6. Fluvial hydrodynamics (food/ Without reference Occurs at both in high and low Tricart (1977), Sternberg (1998) ebb tide) tide and Stevaux and Latubresse (2017) 7. Channel patterns Mostly meandering Mostly meandering Press et al. (2006) 8. Portion of the river concave or Predominately concave Predominately concave CPRM (2016) and Stevaux and convex Latubresse (2017) 9. Width of the river Not mentioned All widths CPRM (2016) 10. Water type All water types Mostly white water, greater sedi- Carvalho (2006) mentary load 11. Geological age of the marginal Tertiary/Quaternary Tertiary/Quaternary CPRM (2016) and Stevaux and slope Latubresse (2017) 12. Slope height and declivity 20 cm to 25 m CPRM (2016) 13. Area eroded Several sizes Predominance of large areas CPRM (2016) 14. Tectonic factors Yes Yes Igreja and Catique (1997) and Costa et al. (1996) 15. Vegetation Decreases intensity of the process Decreases intensity of the process, CPRM (2016) but the phenomenon proceeds regardless 16. Anthropic action (boat trafc) Infuences erosion, but in small Carvalho (2006) proportions 17. Which types of mass move- Undermining, sliding, and creep Undermining CPRM (2016), Suguio and Big- ment are associated with fuvial arella (1990) and Carvalho (2006) erosion, sliding, or undermin- ing?

of roots present in this vegetation (Fernandez 1990). How- which factors infuence fuvial erosion and terras caídas ever, during the feld investigation, it was observed that in and verify whether these processes have the same charac- riverbanks of the Amazon, erosion occurs even with vegeta- teristics or are separate phenomena (Table 2). tion present. Nevertheless, the hydraulic behavior of soils, velocity of infltration, and variation of piezometric level difer with the presence or absence of vegetation; the erosive process proceeds more slowly where vegetation is present Conclusions (Costa et al. 1996; Sutili 2007). The terras caídas process is distinct phenomenon in the Anthropic infuence Amazon. It differs from other forms of fluvial erosion because it is associated with mass movements that trigger Another trigger for undermining is the increased frequency large landslides, which can cause irreversible material dam- of waves caused by boats trafc, which move at high speed. age and loss of life. These processes are linked to seasonal Small waves form that erode the bases of marginal slopes variation of river water level, which causes undermining and thus cause landfalls. No analysis was available to during the high tides, and during the low tides, because of assess the speed and height of waves that provoke erosion. hydrostatic conditions, makes marginal slopes lose resist- Based on preexisting fuvial erosion concepts regarding ance and slip. The loss of cohesiveness of the unconsoli- terras caídas, and the sectorization of risk data in Amazo- dated material of the riverbanks occurs from mainly in nia (CPRM 2016), the information was compiled to assess alluvial sediments saturated during the foods. Therefore,

1 3 Environmental Earth Sciences (2018) 77:222 Page 15 of 16 222 abrasive erosion in the riverbank and great magnitude mass Brazilian Seismographic Network (2014) Brazilian Seismic Bulletin, movements strike in terras caídas phenomenon. v2014.06. http://www.rsbr.gov.br/catal​ogo_sb.html. Accessed 7 June 2017 (in Portuguese) However, geotechnical studies to assess the mechani- Carvalho JAL (2006) Terras caídas and social consequences: Miracau- cal properties of the material the riverbank to the Amazon era Coast—Paraná da Trindade, Municipality of Itacoatiara—AM, region are insufcient. The modifcations of soil characteris- Brazil. Dissertation, Federal University of Amazonas—UFAM tics during diferent hydrostatic pressures that increase bank (in Portuguese) Carvalho JAL, Cunha SB, Igreja HLS, Carneiro DS (2009) Episodes of erodibility are not currently known. Deeper studies are also Terras Caídas on the Amazonas River: the case of Costa da Águia, needed to analyze the direct infuence of neotectonics, strong Parintins–AM. In: Brazilian Symposium on Water Resources, winds, and anthropic activity on terras caídas occurrence Campo Grande. Anais. Porto Alegre: Brazilian Association of and distribution. Water Resources. http://www.abrh.org.br/sgcv3/UserF​ iles/Sumar​ ​ ios. Accessed 10 Aug 2016 (in Portuguese) More detailed studies are required, such as temporal anal- Christofoletti A (1980) Geomorphology. Edgard Blücher, São Paulo ysis of erosion rates, determining the fow velocity needed to (in Portuguese) break the resistance of material cause erosion, verifcation of Costa JBS, Bemerguy RL, Hasui Y, Borges MS, Ferreira Júnior CRP, the infuence of sedimentary charge on the erosive process, Bezerra PEL, Costa ML, Fernandes JMG (1996) Neotectonics of the Amazon Region: tectonic, geomorphological and depositional studies of the efects of wind and waves on this process, as aspects. GEONOMOS 4:23–44 (in portuguese) well as testing with explosives to determine the magnitudes Couper P (2003) Efects of silt–clay content on the susceptibility of of earthquakes that could generate sliding. These fndings, river banks to subaerial erosion. Geomorphology 56(1–2):95–108 in conjunction with pluviometric studies and statistics of CPRM-Mineral Resources Research Company (2004) Geological Chart of Brazil to the Millionth of Leaves SC. 18—Contamana e SC. the hydrodynamic and morphological parameters of rivers, 19—Rio Branco. Rio Branco: 1 map, color. Scale: 1:1.000.000. can be applied to determine which places are prone to terras GIS of Brazil. Geology of Brazil Program (in Portuguese) caídas, and thus serve as a resource for land-use planning CPRM-Mineral Resources Research Company (2011) Pluviometric and management for the riverside population. Atlas of Brazil. Brasília. http://www.cprm.gov.br/publique/media​ ​ /Isoie​tas_Totai​s_Anuai​s_1977_2006.pdf. Accessed 4 Dec 2016 Acknowledgements (in Portuguese) The authors would like to thank the Geological CPRM-Mineral Resources Research Company (2014) Emergency Survey of Brazil, for a feld support and risk sectors information of action for the recognition of areas of high and very high risk of the study area. mass movements and foods in the Municipality of Ipixuna, State of Amazonas. Manaus: CPRM, 1. http://www.cprm.gov.br/publi​ que/Gesta​o-Terri​toria​l/Geolo​gia-de-Engen​haria​-e-Risco​s-Geolo​ gicos​/Setor​izaca​o-de-Risco​s-Geolo​gicos​-4138.html. Accessed 4 References June 2016 (in Portuguese) CPRM-Mineral Resources Research Company (2016) Sectorization of risk. http://www.cprm.gov.br/publi​que/Gesta​o-Terri​toria​l/Geolo​ Adamy A (2010) Geological hazards. In: Adamy A (org) Geodiversity gia-de-Engen​haria​-e-Risco​s-Geolo​gicos​/Setor​izaca​o-de-Risco​ of the State of Rondônia. Mineral Resources Research Company s-Geologicos​ -4138.html​ . Accessed 10 Dec 2016 (in Portuguese) (CPRM), Porto Velho, pp 133–147 (in Portuguese) Cunha SB (1995) Impacts of engineering works on the biophysical Alexander JS, Wilson RC, Green WR (2012) A brief history and sum- environment of the São João River Basin (—Bra- mary of the efects of river engineering and dams on the Missis- zil). Institute of Geosciences of the Federal University of the Rio sippi River system and delta. U.S. Geological Survey Circular, de Janeiro—UFRJ, Rio de Janeiro (in Portuguese) 1375, Reston, VA (U.S. Geological Survey). http://pubs.usgs.gov/ Das T, Haldar SK, Gupta ID, Sen S (2014) River bank erosion circ/1375/. Accessed 26 Apr 2017 induced human displacement and its consequences. Living Rev ANA-National Water Agency (2009) State of afairs of Brazil’s water Landsc Res 8:3 resources. ANA, Brasília. http://www3.snirh​.gov.br/porta​l/ Fernandez OVQ (1990) Changes in the Paraná River channel and ero- snirh​/centr​ais-de-conte​udos/conju​ntura​-dos-recur​sos-hidri​cos. sion processes in the banks: Porto Rico Region-PR. Dissertation, Accessed 12 May 2017 (in Portuguese) Institute of Geosciences and Exact Sciences of the São Paulo ANA-National Water Agency (2015) State of afairs of Brazil’s water State University—IGCE/UNESP, Rio Claro (in Portuguese) resources: Brazilian hydrographic regions—Special edition. ANA, Ferreira AL, Reis NJ, Riker SL, Almeida ME (2007) Geological map Brasília. http://www3.snirh​.gov.br/porta​l/snirh​/centr​ais-de-conte​ of the State of Amazonas. Manaus: CPRM-Mineral Resources udos/conjuntura​ -dos-recur​ sos-hidri​ cos/regio​ eshid​ rogra​ fcas​ 2014.​ Research Company. 1 map, color. Scale 1:1.000.000.000 (Geol- pdf. Accessed 15 Jan 2017 (in Portuguese) ogy of Brazil Program). http://www.cprm.gov.br/publi​que/ ANA-National Water Agency (2016) Information of water resources: Geolo​gia/Geolo​gia-Basic​a/Carto​graf​a-Geolo​gica-Regio​nal- Report 2016/National Water Agency - Brasília: ANA. http:// 624.html. Accessed 26 Jan 2017 (in Portuguese) www3.snirh​.gov.br/porta​l/snirh​/centr​ais-de-conte​udos/conju​ Figueiredo JL (1945) Terras caídas. Geographical Bulletin, Rio de ntura​-dos-recur​sos-hidri​cos/infor​me-conju​ntura​-2016.pdf/view. Janeiro (in Portuguese) Accessed 12 May 2017 Filizola N, Guyot JL, Molinier M, Guimarães V, Oliveira E, Freitas ANA-National Water Agency (2017). http://hidroweb.ana.gov.br/defau​ ​ MA (2002) Hydrological characterization of the . lt.asp. Accessed 15 Jan 2017 (in Portuguese) In: Rivas AAF, Freitas CEC (eds) Amazonia: an interdiscipli- BRAZIL (2012) Law no. 12.608 of April 10, 2012. Establishes the nary perspective. University of Amazonas Publishing, Manaus National Policy for Protection and Civil Defense. Civil House. (in Portuguese) Section for legal afairs. http://www.plana​lto.gov.br/ccivi​l_03/_ Freitas FT (2009) Multi-temporal analysis of the erosive modal- Ato20​11-2014/2012/Lei/L1260​8.htm. Accessed 2 Aug 2017 ity of “Terra Caída” in the Médio Solimões region—Coari/AM,

1 3 222 Page 16 of 16 Environmental Earth Sciences (2018) 77:222

Dissertation, Faculty of Humanities, Federal University of Amazo- Quiroga DRA, Gil V, Coronato A (2017) Quantitative geomorphology nas, Manaus (in Portuguese) applied to fuvial dynamic in Aviles and Moneta basins, Tierra Del Freitas FT, Albuquerque AR (2012) Temporal analysis on the “Terras Fuego, Southern Argentina. Environ Earth Sci 76:188 Caídas” in Solimões/Coari (AM). Mercator Fortaleza 11(25):129– Rai PK, Mohan K, Mishra S, Ahmad A, Mishra VN (2017) A GIS-based 140 (in Portuguese) approach in drainage morphometric analysis of Kanhar River Basin, Guerra AT (1993) Geomorphological geological dictionary, 8th edn. Bra- India. Appl Water Sci 7:217–232 zilian Institute of Geography and Statistics—IBGE, Rio de Janeiro Riccomini C, Giannini PCF, Mancini F (2000) Rivers and alluvial pro- (in Portuguese) cesses. In: Teixeira W, Toledo MCM, Fairchild TR, Taioli F (Org) Hjulstrom F (1939) Transportation of debris by moving water. In: Trask Deciphering earth. Ofcina de Texto, São Paulo, pp 191–214 (in PD (ed) Recent marine sediments; a symposium. American Associa- Portuguese) tion of Petroleum Geologists, Tulsa, pp 5–31 Rinaldi M, Casagli N, Dapporto S, Gargini A (2004) Monitoring and Igreja HLS, Catique JA (1997) Neotectonic analysis of the Itacoatiara- modelling of pore water pressure changes and riverbank stability eastern boundaries of the State of Amazonas. In: National Sympo- during fow events. Earth Surf Process Landf 29:237–254 sium of Tectonic Studies, 6, Belém. Anais. Belém: SBG/NO, pp Rodrigues FGS (2014) The concept of “terras caídas” and the fuvial 131–133 (in Portuguese) morphodynamics caracterization of the high Solimões river. Revista Jones LS, Schumm SA (1999) Causes of avulsion: an overview. In: Smith Geonordeste São Cristóvão Ano 26(3):4–23 ND, Rogers J (eds) Fluvial sedimentology, VI Rotta CMS, Zuquette LV (2014) Erosion feature reclamation in urban Jung HC, Hamski J, Durand M, Alsdorf D, Hossain F, Lee H, Azad areas: typical unsuccessful examples from Brazil. Environ Earth Hossain AKM, Hasan K, Khan AS, Hoque AKM (2010) Charac- Sci 72:535–555 terization of complex fuvial systems using remote sensing of spa- Scherer CMS (2008) River environments. In: Pedreira da Silva AJCL, tial and temporal water level variations in the Amazon, Congo, and Aragão MANF, Magalhães AJC (Org.) Sedimentation environments Brahmaputra Rivers. Earth Surf Process Landf 35:41–151. http:// of Brazil. Rio de Janeiro, pp 102–130 (in Portuguese) periodicos​ .uem.br/ojs/index​ .php/Geoin​ ga/artic​ le/view/18015​ /9784​ . Schumm SA (1993) River response to base level change: implications Accessed 12 Apr 2017 for sequence stratigraphy. J Geol, 100th Anniversary Symposium: Junk WJ (ed) (1997) The Central Amazon foodplain: ecology of a puls- Evolution of the Earth’s Surface, 101(2): 279–294 ing system. In: Ecological studies, vol 126. Springer, Berlin, pp Sioli H (ed) (1984) The Amazon: limnology and landscape ecology of a 223–226. https​://doi.org/10.1007/978-3-662-03416​-3 mighty tropical river and its basin. Dr. Junk, Hague-Boston Lancas- Labadessa AS (2011) “Terras Caídas”, natural and anthropogenic causes: ter. https​://doi.org/10.1007/97894​00965​423 a case study in the community of São Carlos—Médio Madeira/RO. Springer FM Jr, Ullrich CR, Hagerty DJ (1985) Streambank stability. J Geoingá J Grad Prog Maringá Geogr 3(1):45–61. http://perio​dicos​ Geotech Eng 111(5):624–640 .uem.br/ojs/index.php/Geoin​ ga/artic​ le/view/18015​ /9784​ . Accessed Sreedevi PD, Sreekanth PD, Khan HH, Ahmed S (2013) Drainage mor- 12 June 2016 (in Portuguese) phometry and its infuence on hydrology in a semiarid region: using Latrubesse EM, Franzinelli E (2002) The Holocene alluvial plain of the SRTM data and GIS. Environ Earth Sci 70:839–848. https​://doi. middle Amazon River, Brazil. Geomorphology 44:241–257 org/10.1007/s1266​5-012-2172-3 Lawler DM, Thorne CR, Hooke JM (1997) Bank erosion and instability. Sternberg HO’R (1998) Water and man in foodplain. Emílio In: Thorne CR, Hey RD, Newson MD (eds) Applied fuvial geomor- Goeldi Pará Museum, Belém (in Portuguese) phology for river engineering and management. Wiley, Chichester, Stevaux JC, Latubresse EM (2017) River geomorphology. Ofcina de pp 137–172 Texto, São Paulo (in Portuguese) Li X, Zhou Y, Tian B, Kuang R, Wang L (2015) GIS-based methodology Suguio K, Bigarella JJ (1990) River environments. Federal University of for erosion risk assessment of the muddy coast in the Yangtze Delta. Santa Catarina Publisher—EDUFSC, Florianópolis (in Portuguese) Ocean Coast Manag 108:97–108 Sutili FJ (2007) Bioengineering of soils in the fuvial environment of Milliman JD, Meade RH (1983) World-wide delivery of river sediment southern Brazil. Ph.D., Department of Civil Engineering and Natu- to the oceans. J Geol 91:1–21 ral Hazards, Institute of Soil Bioengineering and Landscape Plan- Novo EMLM. (2008) River environments. In: Florenzano TG (Org.) Geo- ning, Rural University of Vienna, Vienna (in Portuguese) morphology: current concepts and technologies. Ofcina de Textos, Teixeira SG (2010) Geological hazard. In: Maia MAM, Marmos JL (org) São Paulo, pp 219–236 (in Portuguese) Geodiversity of the State of Amazonas. Mineral Resources Research Oliveira Filho IB, Adamy A (2015) Geological hazards. In: Adamy A Company—CPRM, Manaus, pp 87–100 (in Portuguese) (org) Geodiversity of the State of Acre. Mineral Resources Research Tricart J (1977) Types of alluvial plains and river beds of the Brazilian Company—CPRM, Porto Velho, pp 131–144 (in Portuguese) Amazon. Braz J Geogr, Rio de Janeiro, pp 3–37 (in Portuguese) Passos MS, Soares EAA (2017) Multi-temporal analysis of the Solimões- Uddin AFM, Basak JK (2012) Efects of riverbank erosion on Livelihood, Amazonas river system between the Purus and Negro tributaries, in centre for research and action on development. Report of Unnayan Western Amazon, Brazil. Geology USP, Scientifc Series, São Onneshan Centre for Research and Action on Development. p 39 Paulo, 17(1):61–74 (in Portuguese) UFSC-CEPED-Federal University of Santa Catarina. University Center for Pereira HG, Andretta ER (2010) Diagnosis of the risk areas located Studies and Research on Disasters (2013). Brazilian Atlas of Natural along the edge of the Municipality of Barrerinha—AM. Final Disasters 1991–2012: volume Brazil. Florianópolis (in Portuguese) report. Mineral Resources Research Company—CPRM, Manaus Valeriano MM, Rosseti DF (2008) Topographic modeling of Marajó (in Portuguese) island with SRTM data. Revista Brasileira de Geomorfologia Press F, Siever R, Grotzinger J, Jordan TH (2006) Understanding earth. 9(1):53–64 Rualdo Menegat translation, 4th edn. Bookman, Porto Alegre (in Vasquez ML, Sousa CS, Carvalho JMA (2008) Geological map of the Portuguese) State of Pará. Belém: CPRM- Mineral Resources Research Com- Quadros ML, Rizzotto GJ (Org.) (2007) Geological map and mineral pany. 1 map, color. Scale 1:1.000.000.000 (Geology of Brazil Pro- resources of the State of Rondônia. Porto Velho: CPRM-Mineral gram). http://www.cprm.gov.br/publique/Geolo​ gia/Geolo​ gia-Basic​ ​ Resources Research Company. 1 map, color. Scale 1:1.000.000 a/Cartograf​ a-Geolo​ gica-Regio​ nal-624.html​ . Accessed 26 Jan 2017 (Geology of Brazil Program). http://www.cprm.gov.br/publi​que/ (in Portuguese) Geolo​gia/Geolo​gia-Basic​a/Carto​graf​a-Geolo​gica-Regio​nal-624. html. Accessed 26 Jan 2017 (in Portuguese)

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