Alluvial terraces on the Ionian coast of northern Calabria, southern Italy: Implications for tectonic and sea level controls

In this paper we present the results of an integrated geomorphological, pedological and stratigraphical study carried out along the Ionian coast of northern Calabria (southern Italy). This area is characterised by the occurrence of five orders of alluvial terraces that are striking features of the landscape, where large and steep catchments debouch from the mountain front to the hilly coastal belt.Field investigations indicate that the deposits of all five terraces are suggestive of shallow gravel-bed braided streams.On the basis of the age of the Pleistocene substratum and morphostratigraphic correlation with marine terraces cropping out in the nearby areas, each order has been associated to specific marine oxygen isotope stages.Consequently, we focused on the interplay of allocyclic factors influencing stream aggradation/degradation. Soil features and other climatic proxies suggest that climate didn't play an important role with respect to tectonic and base-level changes in controlling fluvial dynamics.In particular, we recognised that during the middle Pleistocene the study area experienced a period of subaerial landscape modelling, as suggested by the thick and complex alluvial sequence of the highest terrace (T1). The onset of regional uplift marks a change in the geomorphic scenario, with tectonic and eustatically driven changes in base-level working together in causing switches in fluvial aggradational/erosional phases (T2–T5 terraces). Because of the uplift, river dissection occurred during phases of sea level fall, whereas aggradation phases occurred during periods of climate amelioration (sea level rise) just before highstands were attained.As a consequence, the stepped terraces in the study area reflect the interplay between tectonics (uplift) and sea level changes, in which terraces define episodes of relative sea level fall during the late Quaternary.     

Soil erosion risk scenarios in the Mediterranean environment using RUSLE and GIS: An application model for Calabria (southern Italy)

Soil erosion by water (WSE) has become a relevant issue at the Mediterranean level. In particular, natural conditions and human impact have made the Calabria (southern Italy) particularly prone to intense WSE. The purpose of this investigation is to identify areas highly affected by WSE in Calabria by comparing the scenarios obtained by assuming control and preventive measures and actions, as well as actual conditions generated by forest fires, also in the presence of conditions of maximum rainfall erosion.Geographic Information System techniques have been adopted to treat data of reasonable spatial resolution obtained at a regional scale for application to the RUSLE model. This work is based on the comparison of such data with a basic scenario that has been defined by the present situation (present scenario). In this scenario: (i) R has been assessed by means of an experimental relation adjusted to Calabria on the basis of 5-min observations; (ii) K has been drawn from the soil map of Calabria including 160 soilscapes; (iii) LS has been estimated according to the RUSLE2 model by using (among other subfactors) a 40-m square cell DTM; (iv) C has been derived by processing the data inferred from the project Corine Land Cover, whose legend includes 35 different land uses on three levels; and (v) P has been hypothesized as equal to 1.For the remaining three hypothesized scenarios, the RUSLE factors have been adjusted according to experimental data and to data in the literature. In particular, forest areas subject to fire have been randomly generated as far as fire location, extension, structure, and intensity are concerned.The values obtained by the application of the RUSLE model have emphasized that land management by means of measures and actions for reducing WSE causes a notable reduction of the erosive rate decreasing from ~30 to 12.3 Mg ha^− 1 y^− 1. On the other hand, variations induced by hypothetical wildfires in forests on 10% of the regional territory bring WSE over the whole region to values varying from 30 to 116 Mg ha^− 1 y^− 1.This study can be offered to territorial planning authorities as an evaluation instrument as it highlights the merits and limitations of some territorial management actions. In fact, in Calabria no observations exist concerning the implications of these actions.     

Quaternary normal faulting in southeastern Sicily (Italy):a seismic source for the 1693 large earthquake

We present geological and morphological data, combined with an analysis of seismic reflection lines across the Ionian offshore zone and information on historical earthquakes, in order to yield new constraints on active faulting in southeastern Sicily. This region, one of the most seismically active of the Mediterranean, is affected by WNW–ESE regional extension producing normal faulting of the southern edge of the Siculo–Calabrian rift zone. Our data describe two systems of Quaternary normal faults, characterized by different ages and related to distinct tectonic processes. The older NW–SE-trending normal fault segments developed up to ≈400  kyr ago and, striking perpendicular to the main front of the Maghrebian thrust belt, bound the small basins occurring along the eastern coast of the Hyblean Plateau. The younger fault system is represented by prominent NNW–SSE-trending normal fault segments and extends along the Ionian offshore zone following the NE–SW-trending Avola and Rosolini–Ispica normal faults. These faults are characterized by vertical slip rates of 0.7–3.3  mm  yr ⁻¹ and might be associated with the large seismic events of January 1693. We suggest that the main shock of the January 1693 earthquakes ( M ~ 7) could be related to a 45  km long normal fault with a right-lateral component of motion. A long-term net slip rate of about 3.7  mm  yr ⁻¹ is calculated, and a recurrence interval of about 550 ± 50  yr is proposed for large events similar to that of January 1693.     

Oligocene to Early Miocene sedimentation and tectonics in the southern part of the Calabrian-Peloritan Arc (Aspromonte, southern Italy): a record of mixed-mode piggy-back basin evolution

The Calabrian-Peloritan Arc (southern Italy) represents a fragment of the European margin, thrusted onto the Apennines and Maghrebides during the Europe-Apulia collision in the late Early Miocene. A reconstruction of the pre-Middle Miocene tectono-sedimentary evolution of the southern part of the Calabrian-Peloritan Arc (CPA) is presented, based on a detailed analysis of the Stilo-Capo ?Orlando Formation (SCO Fm). Deposition of the SCO Fm occurred in a series of mixed-mode piggy-back basins. Basin evolution was controlled by two intersecting fault systems. A NW-SE oriented system delimited a series of sub-basins and fixed the position of feeder channels and submarine canyons, whereas a NE-SW oriented system controlled the axial dispersal of coarse-grained sediments within each of the sub-basins. From base to top, sedimentary environments change from terrestrial and lagoonal to upper bathyal over a timespan of approximately 12 Myr (late Early Oligocene-late Early Miocene). During this interval, extensional tectonic activity alternated with oblique backthrusting events, related to dextral transpression along the NW-SE oriented faults. This produced a characteristic pulsating pattern of basin evolution. Oligocene-Early Miocene evolution of the W. Mediterranean basin was dominated by ‘roll back’ of the Neotethyan oceanic lithosphere. Considerable extension in the overriding European Plate gave rise to the formation of a back arc-thrust system. The initial stages of Calabrian Basin evolution are remarkably similar to the evolution of rift basins in the back arc (Sardinia). The Calabrian basins, which are inferred to have originated as thin-skinned pull-apart basins, were subsequently incorporated into the Apennines-Maghrebides accretionary wedge by out-of-sequence thrusting, and became decoupled from the back arc. Periodic restabilization of the accretionary wedge, resulting in an alternation of backthrusting and listric normal faulting, provides an explanation for the structural evolution of these mixed-mode basins. The basins of the southern part of the CPA may be termed ‘spanner’ or ‘looper’ basins, in view of their characteristic pulsating structural evolution, superimposed upon their migration toward the foreland. This new term adequately accounts for the occurrence of tectonic inversions in long-lived piggy-back basins, as expected in the light of the dynamics of accretionary wedges.     

The Miocene tectono-sedimentary evolution of the southern Tyrrhenian Sea: stratigraphy, structural and palaeomagnetic data from the on-shore Amantea basin (Calabrian Arc, Italy)

We report on new stratigraphic, palaeomagnetic and anisotropy of magnetic susceptibility (AMS) results from the Amantea basin, located on‐shore along the Tyrrhenian coast of the Calabrian Arc (Italy). The Miocene Amantea Basin formed on the top of a brittlely extended upper plate, separated from a blueschist lower plate by a low‐angle top‐to‐the‐west extensional detachment fault. The stratigraphic architecture of the basin is mainly controlled by the geometry of the detachment fault and is organized in several depositional sequences, separated by major unconformities. The first sequence (DS1) directly overlaps the basement units, and is constituted by Serravallian coarse‐grained conglomerates and sandstones. The upper boundary of this sequence is a major angular unconformity locally marked by a thick palaeosol (type 1 sequence boundary). The second depositional sequence DS2 (middle Tortonian‐early Messinian) is mainly formed by conglomerates, passing upwards to calcarenites, sandstones, claystones and diatomites. Finally, Messinian limestones and evaporites form the third depositional sequence (DS3). Our new biostratigraphic data on the Neogene deposits of the Amantea basin indicate a hiatus of 3 Ma separating sequences DS1 and DS2. The structural architecture of the basin is characterized by faulted homoclines, generally westward dipping, dissected by eastward dipping normal faults. Strike‐slip faults are also present along the margins of the intrabasinal structural highs. Several episodes of syn‐depositional tectonic activity are marked by well‐exposed progressive unconformities, folds and capped normal faults. Three main stages of extensional tectonics affected the area during Neogene‐Quaternary times: (1) Serravallian low‐angle normal faulting; (2) middle Tortonian high‐angle syn‐sedimentary normal faulting; (3) Messinian‐Quaternary high‐angle normal faulting. Extensional tectonics controlled the exhumation of high‐P/low‐T metamorphic rocks and later the foundering of the Amantea basin, with a constant WNW‐ESE stretching direction (present‐day coordinates), defined by means of structural analyses and by AMS data. Palaeomagnetic analyses performed mainly on the claystone deposits of DS1 show a post‐Serravallian clockwise rotation of the Amantea basin. The data presented in this paper constrain better the overall timing, structure and kinematics of the early stages of extensional tectonics of the southern Tyrrhenian Sea. In particular, extensional basins in the southern Tyrrhenian Sea opened during Serravallian and evolved during late Miocene. These data confirm that, at that time, the Amantea basin represented the conjugate extensional margin of the Sardinian border, and that it later drifted south‐eastward and rotated clockwise as a part of the Calabria‐Peloritani terrane.     

Quaternary tectonics and large-scale gravitational deformations with evidence of rock-slide displacements in the Central Apennines (central Italy)

Eight cases of large-scale gravitational movements (with evidence of rock-slide type displacements) evolving close to Quaternary faults have been analysed in the Central Apennines. Geomorphological and structural surveys have defined the relationship between the gravitational displacements and the tectonically-controlled modifications of the landscape. The evolution of all the investigated cases has been conditioned by the presence of fault planes located along the mountain slopes. In most cases (Mt. Cefalone, Cima della Fossa, Villavallelonga, Casali d'Aschi, Gioia dei Marsi), the faults played or are playing a primary role in increasing the local relief and their activity represents the main geomorphic factor conditioning the gravitational movements. This kind of relationship has been observed along mountain slopes bordering depressions which have not been drained for most of their geomorphic history or have been characterised by an evolution of the hydrographic network that has been conditioned only by the local tectonic subsidence. In such cases, the gravitational movements develop in the footwalls of the faults. In other cases (Fiamignano, Pescasseroli) the faults have played a passive role, since they only bound the sliding masses and coincide with the surficial expressions of the sliding planes. Therefore, the gravitational displacements develop in the hangingwall of the faults. The evolution is conditioned by the incision of the hydrographic network in response to regional Quaternary uplift. The illustrated case studies provide a wide range of examples of the gravitational response of slopes to the modifications of the landscape due to linear and areal tectonics. The identification of the geomorphic traces of the large-scale gravitational movements along fault-controlled mountain fronts has implications for hazard, particularly for the evolution of the displacement. The quantitative analysis of the vertical displacements and data on the characteristics of the surface breaking during historical earthquakes demonstrate that along-fault offsets strongly increases where the unstable large-scale rock masses are located. Therefore, the large coseismic vertical offset may represent a major problem for the displacement of utilities and may represent a potential cause for the sudden and catastrophic evolution of the gravitational movement.     

中国第四纪冰川演化序列与MIS对比研究的新进展

近年来,随着多种可对冰川地形进行直接定年的测年技术的发展与应用,中国第四纪冰川研究取得了新进展,较为突出的是获得了大量与地貌地层关系相符的年代学资料、建立了冰川演化若干典型范例以及进一步确立了青藏高原构造隆升与冰川发育的耦合关系。中国第四纪冰川演化序列与海洋氧同位素阶段(Marine Oxygen Isotope Stage,MIS) 比较经历了2000 年、2002 年两次立案与改进。笔者基于近年来新测得的年代学数据、已建立的冰川演化序列以及青藏高原隆升与冰川发育的耦合关系等新的研究资料,提出了中国冰期与海洋氧同位素阶段比较的2011 年改进方案,包括近百万年冰川变化的15 个特征时段及其对应的时间与中国冰期名称等信息。     

Effects of tectonics and lithology on long profiles of 16 rivers of the southern Central Massif border between the Aude and the Orb (France)

The analysis of longitudinal profiles of river channels and terraces in the southern Central Massif border, between the Aude and the Orb, allows the detection of anomalies caused by lithology and/or tectonic distortions. The rivers which have abnormally high slope and non-lithological knickzones indicate the main uplifted zones: the Montagne Noire and the Saint-Chinian ridge. A geomorphological and sedimentological analysis of detrital deposits was carried out as a basis for correlating the different formations, reconstructing the palaeodrainage and finding the main uplift and fluvial incision stages. During the Miocene, uplift remains limited as it is shown by the correlative fine deposits in the Languedocian piedmont. The Messinian incision (5.7–5.3 Ma) does not cross the Saint-Chinian ridge. On the other hand, fluvial incision becomes widespread in the Montagne Noire during the Upper Pliocene (3.4–2 Ma) when coarse deposits overlie either the Pliocene clay in the Orb palaeovalley or the Messinian conglomerates at the Cesse outlet. An Upper Pliocene uplift of the Montagne Noire and of the Saint-Chinian ridge is the cause of this incision and also of the diversion of the Cesse towards the Aude. Where the uplift rate was higher than incision rate, knickzones have developed like in the Avant-Monts south-side. The knickzones of lithological origin maintain a strong vertical stability during all the river incision stages. On the other hand, those of tectonic origin or base level lowering record upstream migration and their rate of retreat is controlled by the river discharge. As incision occurs only during the cold/temperate transition periods during the Quaternary, upward erosion slowly migrates (15 km since the Upper Pliocene, on the Orb) and so does not reach the riverheads.     

Large rockslides in the Southern Central Andes of Chile (32–34.5°S): Tectonic control and significance for Quaternary landscape evolution

The distribution and age of large (> 0.1 km²) Pliocene to recent rockslides in the Chilean Cordillera Principal (32–34.5 S), the Southern Central Andes, has been analyzed to determine the rockslide triggering mechanisms and impact on regional landscape evolution. Most of the rockslides appear in the western Cordillera Principal and cluster along major geological structures. Variographic analyses show spatial correlation between rockslides, geological structures and shallow seismicity. A relative chronosequence was calibrated with existing ¹⁴C and ⁴⁰Ar/³⁹Ar dates and new cosmogenic nuclide exposure ages for selected rockslides. Rockslide-induced sediment yield was estimated with empirical relations for rockslide area distributions. Throughout the Quaternary, rockslides have delivered sediment to streams at rates equivalent to denudation rates of 0.10 ±0.06 mm a^− 1, while estimates using short term (20 a) seismicity records are 0.3_− 0.2^+ 0.6 mm a^− 1. The estimates of sediment transfer and the spatial distribution of rockslides reflect a landscape in which tectonic and geological controls on denudation are more significant than climate.     

The role of strong earthquakes and tsunami in the Late Holocene evolution of the Fortore River coastal plain (Apulia, Italy): A synthesis

Morphological analysis of the Fortore River coastal plain and the Lesina Lake coastal barrier integrated with radiocarbon age data indicates that the evolution of the coastal landscape has been strongly affected by a number of strong earthquakes and related tsunamis which occurred during the last 3000 years. The first seismic event struck this coastal area in the V century BC. It produced strong erosion of the Fortore River coastal plain and significant emersion of Punta delle Pietre Nere, as well as the large tsunami responsible for the development of the Sant'Andrea washover fan. The second event occurred in 493 AD; it induced severe erosion of the Fortore River coastal plain and triggered the large tsunami that hit the Lesina Lake coastal barrier, producing the Foce Cauto washover fan. Then later in 1627, an earthquake was responsible for the further coseismic uplift of Punta delle Pietre Nere, the subsidence of Lesina village area and the development of a tsunami which produced two washover fans.Morphological analysis points out that seismic events strong enough to control the morphological evolution of local coastal landscapes show a statistical return period of about 1000 years. These major events produced important coseismic vertical movements and large tsunamis. However, the correct identification of the tectonic structure responsible for the generation of these strong earthquakes is still an unsolved problem.     

Field monitoring of the Corvara landslide (Dolomites, Italy) and its relevance for hazard assessment

The Corvara landslide is an active slow moving rotational earth slide - earth flow, located uphill of the village of Corvara in Badia, one of the main tourist centres in the Alta Badia valley in the Dolomites (Province of Bolzano, Italy). Present-day movements of the Corvara landslide cause National Road 244 and other infrastructures to be damaged on a yearly basis. The movements also give rise to more serious risk scenarios for some buildings located in front the toe of the landslide. For these reasons, the landslide has been under observation since 1997 with various field devices that enable slope movements to be monitored for hazard assessment purposes. Differential GPS measurements on a network of 47 benchmarks has shown that horizontal movements at the surface of the landslide have ranged from a few centimetres to more than 1 m between September 2001 and September 2002. Over the same period, vertical movements ranged from a few centimetres to about 10 cm, with the maximum displacement rate being recorded in the track zone and in the uppermost part of the accumulation lobe of the landslide. Borehole systems, such as inclinometers and TDR cables, have recorded similar rates of movement, with the depths of the major active shear surfaces ranging from 48 m to about 10 m. From these data, it is estimated that the active component of the landslide has a volume of about 50 million m³. In this paper the monitoring data collected so far are presented and discussed in detail to prove that the hazard for the Corvara landslide, considered as the product of yearly probability of occurrence and magnitude of the phenomenon, can be regarded has as medium or high if the velocity or alternatively the volume involved is considered. Finally, it is also concluded that the monitoring results obtained provide a sound basis on which to develop and validate numerical models, manage hazard and support the identification of viable passive and active mitigation measures.     

The late Quaternary evolution of the Negro River, Amazon, Brazil: Implications for island and floodplain formation in large anabranching tropical systems

The Rio Negro has responded significantly in the Late Pleistocene and Holocene to lagged environmental changes largely associated with activity during the last glacial in the Amazon basin. On the basis of geological structure, the Rio Negro can be divided into six distinct reaches that each reflects very marked differential processes and geomorphological styles. No deposits of the Upper Pleniglacial were recognized in the field. The oldest recognizable Late Pleistocene alluvial unit is the Upper Terrace of Middle Pleniglacial age (ca. 65–25 ka) (reach I), tentatively correlated with the oldest terrace identified on the left bank of reach III. At that time, the river was mainly an aggradational bed load system carrying abundant quartz sand, a product of more seasonal conditions in the upper catchment. The late glacial (14–10 ka) is represented by a lower finer-grained terrace along the upper basin (reach I), which was recognized in the Tiquié, Curicuriarí, and Vaupes rivers. At that time, the river carried abundant suspended load as a response to climatic changes associated with deglaciation.Since about 14 ka, the river has behaved as a progradational system, infilling in downstream series a sequence of structurally controlled sedimentary basins or ‘compartments,’ creating alluvial floodplains and associated anabranching channel systems. Reach II was the first to be filled, then reach III, both accumulating mainly sand. Fine deposits increase downstream in reach III and become predominant in some anabranch islands of the distal reach. The lowermost reaches of the Negro (V and VI) have been greatly affected by a rising base level and associated backwater effect from aggradation of the Amazon during late glacial and recent times. Reach V has acted almost entirely as a fine sediment trap. The remarkable Anavilhanas archipelago is the product of Holocene deposition in the upper part of this sedimentary basin; however, suspended sediment load declined about 1.5 ka, prior to the lower part of this basin becoming infilled.The progradational behavior of the Rio Negro, filling tectonic basins as successive sediment traps with sand in the upper basins and fines in the downstream ones, illustrates how a large river system responses to profound changes in Late Quaternary base level and sediment supply. The most stable equilibrium conditions have been achieved in the Holocene in reaches IIb and IIIa, where an anabranching channel and erosional–relictual island system relatively efficiently convey water and sediment downstream. Reaches IIIb and V never achieved equilibrium conditions during the Holocene, characterised as they are today with incomplete floodplains and open water.     

Upper-crustal structure of the Benevento area (southern Italy): fault heterogeneities and potential for large earthquakes

The Benevento region is part of the southern Apennines seismogenic belt, which experienced large destructive seismic events both in historical and in recent times. The study area lies at the northern end of the Irpinia fault, which ruptured in 1980 with a M_s = 6.9 normal faulting event, which caused about 3000 casualties. The aims of this paper are to image lateral heterogeneities in the upper crust of the Benevento region, and to try to identify the fault segments that are expected to generate such large earthquakes. This work is motivated by the recognition that lithological heterogeneities along major fault zones, inferred from velocity anomalies, reflect the presence of fault patches that behave differently during large rupture episodes. In this paper, we define the crustal structure of the Benevento region by using the background seismicity recorded during 1991 and 1992 by a local seismic array. These data offer a unique opportunity to investigate the presence of structural discontinuities of a major seismogenic zone before the occurrence of the next large earthquake. The main result that we obtained is the delineation of two NW-trending high-velocity zones (HVZs) in the upper crust beneath the Matese limestone massif. These high velocities are interpreted as high-strength regions that extend for 30-40 km down to at least 12 km depth. The correspondence of these HVZs with the maximum intensity regions of historical earthquakes (1688 AD, 1805 AD) suggests that these anomalies delineate the extent of two fault segments of the southern Apenninic belt capable of generating M = 6.5⁻⁷ earthquakes. The lateral offset observed between the two segments from tomographic results and isoseismal areas is possibly related to transverse right-lateral faults.     

U- and Th-series disequilibria in coastal infill sediments from Praia da Rocha (Algarve Region, Portugal): a contribution to the study of late Quaternary weathering and erosion

U- and Th-series disequilibria observed in a sequence of infill sediments from Praia da Rocha, southern Portugal, were used in combination with geochemical and particle size data to investigate sediment provenance with a view to resolving the late Quaternary weathering and erosion history of the Algarve region, and the stratigraphy of coastal karstic exposures of the Faro/Quarteira (FQ) formation. The red infill units can be distinguished from the brown and buff units on the basis of their lower residual U- and Th-concentrations, their differing post-depositional histories (as revealed by U- and Th-series disequilibria in sequentially extracted sediment phases), and their greater degree of sediment processing. Hence, the buff and brown infill units appear to be derived locally from weathering of the Miocene limestone whilst the red infill may be linked to large-scale mass movement of the FQ formation from further inland, but south of Silves, during the Late Pleistocene. This sequence of events confirms a close association between the formation of karst topography and infilling by gravitational slumping, debris flow and fluvial activity, and, hence, accounts for the complex (three-stage) sediment provenance of the infill material.     

Tectonic and climatic controls on historical landscape modifications: The avulsion of the lower Cecina River (Tuscany, central Italy)

Integration of geomorphology, stratigraphy, sedimentology and morphotectonics in the analysis of the lower Cecina River reach, coastal Tuscany, reveals an undocumented historical channel avulsion. Geomorphological evidence and radiocarbon dating support that, from the Last Glacial Maximum until the end of the 16th century, the Cecina River flowed north of the present course and formed a well-developed cuspate delta. Two concurrent factors, active tectonics as a preparing factor and discharge regime as an activation factor, are thus inferred to have favored the avulsion of Cecina River. Fragmentary archaeological and historical records indicate that the late Holocene Cecina River plain was virtually unpopulated until the latest 16th century. This seems the main reason why high-magnitude hydrological events and prominent river channel avulsions were not reported in historical chronicles. From this perspective, geomorphological data may provide important knowledge and understanding of recent dynamics of environmental change when historical record is lacking or missing.     

Stability of streambanks formed in partially saturated soils and effects of negative pore water pressures: the Sieve River (Italy)

Streambanks of alluvial channels are usually composed of loose materials, which are unsaturated in ambient conditions. Unsaturated soils are subject to negative pore water pressures, which cause an apparent cohesion. The latter is the main factor in allowing the stability of near-vertical banks. Even during moderate in-bank flow events, the apparent cohesion can be strongly reduced as the material approaches full saturation; therefore, during the drawdown phase, as the confining pressure of the water in the channel disappears, a bank failure is likely to occur. Channel bed-level lowering along the Sieve River, Central Italy, has caused widespread bank instability. A geomorphological reconnaissance of forms and processes was followed by in situ tests to determine the shear strength of the banks. Interpretation of the tests and a streambank stability analysis were based on concepts of soil mechanics for unsaturated soils, in order to obtain relations between bank angle and height in limit equilibrium conditions. A stability chart was obtained with curves for different apparent cohesion values, and a stability analysis was performed taking into account the effects of flow events. In order to investigate the pore pressure effects, a series of piezo-tensiometers were installed in a streambank of the Sieve River. Data from a 1 year monitoring period show variations in pore water pressure and matric suction as a consequence of rainfall, evapotranspiration, and water stage variations. A planar failure with a tension crack occurred in the upper cohesive part of the bank during December 1996. The safety factor has been expressed as a function of the geometry of the bank and of the shear strength of the material. Safety factor variations through time are therefore shown as a function of seasonal variations in matric suction.