Mateo Gutiérrez

Erosion rates in badland areas recorded by collectors, erosion pins and profilometer techniques (Ebro Basin, NE-Spain)

Abstract In badland areas of the Ebro Basin, in a semiarid climate, two erosion plots (257 m2; 5° slope and 128 m2; 23° slope) on exposed Tertiary clays were monitored over two years (Nov. 1991–Nov. 1993). This material is characterized by high sodium absorption ratios which lead to high soil dispersivity. The dominant erosion processes in both plots are rilling and sheet erosion. Rainfall intensity was recorded at a weather station, connected to a data-logger, sediment production for single events was collected in tanks, and ground lowering was measured every six months by erosion pins and microtopographic profile gauge techniques. Significant runoff was produced only by rainfall events above 5 mm. Another threshold at 20 mm rain was noted. For rainfalls higher than 20 mm, the 23° slope plot shows a greater runoff response than the 5° one. Rainfall events exceeding this threshold showed a higher sediment production for the steeper slope. In the relationship between precipitation and sediment concentration, an envelope curve can be drawn indicating that any rainfall event of a given amount and intensity has a maximum sediment concentration which we speculate to be a function of the runoff sediment transport capacity. Runoff response and sediment yield in the studied plots are controlled by the rainfall and soil characteristics and their seasonal variations. In both plots, the erosion pins show that erosion rates in rill areas are 25–50% higher than in the interrill areas. Sediment yield recorded by collector devices was higher than the rates measured by erosion pins. The erosion rates based on rill cross-sections by profilometers were higher than the ones recorded by collectors.

Quantitative study of piping processes in badland areas of the Ebro Basin, NE Spain

Abstract In the Ebro Basin, piping is an ubiquitous erosion process in badland areas, occurring in two main situations: on slopes of exposed Tertiary clays and in recently incised silty-clay Holocene valley-fill sediments. The quantitative importance of the main factors controlling piping processes in those conditions was obtained by statistical analysis based on multiple and stepwise regressions. Piping erosion is strongly related to a high sodium absorption ratio (SAR) which favours clay dispersion. However, the statistical analysis indicates that the chemical characteristics and the physical-chemical behaviour are a necessary condition but are not sufficient on their own to develop piping processes. On the slopes, piping is controlled by the physical and chemical properties of the material such as the dispersion index, the granulometric fraction smaller than 4 μm, pH and crack density. In the valley-fill sediments, piping is mainly controlled by the sulphate concentration in the water extract from saturated paste, which is also associated with high SAR values, and the dispersion index. In both geomorphic situations, piping is always related to high crack density and high topographic gradient.

Geomorphological and sedimentological analysis of a catastrophic flash flood in the Arás drainage basin (Central Pyrenees, Spain)

Abstract On August 7th, 1996, an intense and short-duration convective storm occurred over the 18.6-km 2 Aras drainage basin (Central Pyrenees, Spain). This high relief basin is composed of three subbasins, Aso, Betes and La Selva, and feeds the Aras alluvial fan, in the Gallego river valley. This alluvial fan had been drained by an artificial channel (about 125 m 3/s at bank-full capacity). More than 30 check dams in its feeder channel, the Aras barranco, had been previously filled by earlier sediments. The heaviest rain was over the Betes subbasin (total rainfall 178.4 mm; maximum rainfall intensity of 153 mm/h for a 10-min time interval was estimated). Most of the rainfall fell in a 70-min period. This storm resulted in high runoff, causing catastrophic damage and significant geomorphic changes in the drainage basin, especially in the Betes subbasin. The high discharge, concentrated in the Aras barranco, destroyed most of the check dams, flushing out a great amount of debris. Major channel trenching and widening occurred in this barranco. When the confined sediment-laden flash flood reached the basin mouth, it sheet-flooded the southern sector of the Aras fan depositing a massive amount of debris. On this fan 87 people lost their lives and the direct physical damage has been estimated at 55 million dollars. Two stages in the development of the flood have been differentiated from the sedimentological and morphological analysis of the flooded fan lobe. A first stage (peak discharge) of sheet-flooding deposited a coarse boulder lobe, burying the artificial channel at the fan head and causing a darnming effect on the water flood. During the second stage (discharge decline) the flood made its way through the fan head, incising the previous debris accumulation and splitting into two main flow paths.

The stratigraphical record and activity of evaporite dissolution subsidence in Spain

The evaporite formations (in outcrop and at shallow depth) cover an extensive area of the Spanish territory. These soluble sediments are found in diverse geological domains and record a wide time span from the Triassic up to the present day. Broadly, the Mesozoic and Paleogene formations (Alpine cycle) are affected by compressional structures, whereas the Neogene (post-orogenic) sediments remain undeformed.The subsidence caused by subsurface dissolution of the evaporites (subjacent karst) takes place in three main types of stratigraphical settings: a) Subsidence affecting evaporite-bearing mesozoic and Tertiary successions (interstratal karst); b) Subsidence in Quaternary alluvial deposits related to the exorheic evolution of the present-day fluvial systems (alluvial or mantled karst); c) Subsidence in exposed evaporites (uncovered karst). These types may be represented by paleosubsidence phenomena (synsedimentary and/or postsedimentary) recognizable in the stratigraphical record, or by equivalent currently active or modern examples with surface expression.The interstratal karstification of the Mesozoic marine evaporites and the consequent subsidence of the topstrata is revealed by stratiform collapse breccias and wedge-outs in the evaporites grading into unsoluble residues.In several Tertiary basins, the sediments overlying evaporites locally show synsedimentary and/or postsedimentary subsidence structures. The dissolution-induced subsidence coeval to sedimentation gives place to local thickenings in basin-like structures with convergent dips and cumulative wedge out systems. This sinking process controls the generation of depositional environments and lithofacies distribution. The postsedimentary subsidence produces a great variety of gravitational deformations in the Tertiary supra-evaporitic units including both ductile and brittle structures (flexures, synforms, fractures, collapse and brecciation).The Quaternary fluvial terrace deposits on evaporite sediments show anomalous thickenings (>150 m) caused by a dissolution-induced subsidence process in the alluvial plain which is balanced by alluvial aggradation. The complex space and time evolution pattern of the paleosubsidence gives place to intricate and anarchical structures in the alluvium which may be erroneously interpreted as pure tectonic deformations. The current subsidence and generation of sinkholes due to suballuvial karstification constitutes a geohazard which affects to large densely populated areas endangering human safety and posing limitations to the development. An outstanding example corresponds to Calatayud historical city, where subsidence severely damages highly valuable monuments. The subsidence resulting from the underground karstification of evaporites has determined or influenced the generation of some important modern lacustrine basins like Gallocanta, Fuente de Piedra and Banyoles lakes. The sudden formation of sinkholes due to the collapse of cave roofs is relatively frequent in some evaporite outcrops. Very harmful and spectacular subsidence activity is currently occurring in the Cardona salt diapir where subsidence has been dramatically exacerbated by mining practices.

The Jiloca karst polje-tectonic graben (Iberian Range, NE Spain)

Abstract The Jiloca depression, one of the largest morpho-structural units of the Iberian Range and traditionally considered as a neotectonic graben, is interpreted as a karst polje developed within an active halfgraben. This polje, 705 km2 in area, constitutes one of the largest documented poljes. Several evidences—(1) a sequence of eight-stepped levels of corrosion surfaces, (2) the reduced thickness of the basin fill, (3) fault-controlled mountain fronts with topographic scarps much higher than the structural throws—demonstrate that great part of the topographic relief of the depression has been generated by corrosional lowering rather than by tectonic subsidence. The height difference between the highest corrosion surface and the polje bottom indicate that the depression has been deepened around 300 m by corrosion processes. The initiation of the karst polje was determined by the creation of the Jiloca halfgraben by normal faults, which deformed a Pliocene regional erosion surface. The development of the polje has been controlled largely by the asymmetric structure and the slight neotectonic activity of the graben. Changes in the position of the polje bottom inferred from the slopes of the different corrosion surfaces (polje paleotopography) may have been controlled by neotectonic movements.

Scarp retreat rates in semiarid environments from talus flatirons (Ebro Basin, NE Spain)

Abstract Triangular slope facets or talus flatirons are presented as a useful tool for the calculation of scarp retreat rates in arid regions. In the central sector of the Ebro Basin, sequences of talus flatirons have been developed around mesas capped by Miocene limestone. These talus flatirons are grouped in four stages of slope evolution (S2, S3, S4, S5). By the extrapolation of the relict talus profiles with the adjusted log-functions, the position of the scarp for each one of the stages is located. The mean values obtained indicate a scarp retreat of 23 m between stages S3 and S2, 8 m between S4 and S3 and 26 m between S5 and S4. The ages obtained by radiocarbon dating are 2529±52 B.P. and 2930±60 B.P. for stage S2, 27 864±444 B.P. for S3 and 35 570±490 B.P. for S4. Consequently, the mean scarp retreat rates are 0.9 mm/yr for the S2–S3 interval and 1 mm/yr for S3–S4. The scarp retreat rate is related to the lithological and structural features of both the caprock and the underlying clay sediments and to the palaeoclimatic evolution of the region that controls the intensity of weathering and water erosion processes that affect the slope system.

Karst in Gypsum and its environmental impact on the Middle Ebro Basin, Spain

The Middle Ebro Basin in characterised by strong evaporitic profiles from the Miocene period, and in which gypsum formations are predominant. These groups of easy solubility produce in many areas typically karstic landforms, although there are certain features specific to them. The generated landforms appear on the surface as different morphological types of doline, which very often develop on the alluvium deposited by the River Ebro and its affluents. On the agricultural land of the Peñaflor-Villamayor area the functional character of karst causes collapse dolines to appear after heavy storms, and these are constantly filled in by farmers. Motorways and roads that cross these areas, as also the industrial estates existing on the outskirts of Zaragoza, are affected by dissolution processes that bring about continual collapses. The infiltration of water from unlined canals causes the generation of numerous dolines along canal banks.

Paleosubsidence and active subsidence due to evaporite dissolution in Spain

Evaporite formations crop out or are at shallow depth present in an extensive area of Spain. These soluble sediments occur in diverse geological domains and were deposited over a long time span, from the Triassic up to the present day. Broadly, the Mesozoic and Paleogene formations (Alpine cycle) are affected by compressional structures, wheras the Neogene (post-orogenic) sediments remain underformed. Subsidence caused by subsurface dissolution of evaporites (subjacent karst) takes place in three main types of stratigraphic settings: a) subsidence affecting evaporite-bearing Mesozoic and Tertiary successions (interstratal karst); b) subsidence in Quaternary alluvial deposits related to the exorheic evolution of present-day fluvial systems (alluvial or mantled karst); and c) subsidence in exposed evaporites (uncovered karst). These types may be represented by paleosubsidence phenomena (synsedimentary and/or postsedimentary) recognizable in the stratigraphic record, or by equivalent, currently active or modern examples which have a surface expression. Interstratal karstification of Mesozoic marine evaporites, and the consequent subsidence of overlying strata, is revealed by stratiform collapse breccias and wedge outs of the evaporites grading into unsoluble residues. In several Tertiary basins, the sediments overlying evaporites locally show synsedimentary and/or postsedimentary subsidence structures. Dissolution-induced subsidence coeval with sedimentation is accompanied by local thicknening of strata in basin-like structures with convergent dips and cumulative wedge-out systems. This sinking process controls the generation of depositional environments and lithofacies distribution. Postsedimentary subsidence produces a great variety of gravitational deformations in Tertiary supra-evaporitic units, including both ductile and brittle structures (flexures, synforms, fractures, collapse, and brecciation). Quaternary fluvial terrace deposits overlying evaporites show anomalous thickenings (>150m) caused by a dissolution-induced subsidence process in the alluvial plain, which is balanced by alluvial aggradation. The complex evolution (in time and space) of paleosubsidence leads to intricate and chaotic structures in the alluvium, which may be erroneously interpreted as pure tectonic deformations. The current subsidence and generation of sinkholes due to suballuvial karstification constitutes a geohazard which affects large, densely populated areas, and thus endangers human safety and poses limitations on development. An outstanding example can be seen in Calatayud, an important historical city where subsidence has severely damaged highly valuable monuments. Subsidence resulting from the underground karstification of evaporites has caused or influenced the generation of some important modern lacustrine basins, such as Gallocanta, Fuente de Piedra, and Banyoles Lakes. The sudden formation of sinkholes due to collapse of cave roofs is fairly frequent in some evaporite outcrops. Very harmful and spectacular subsidence activity is currently occurring in the Cardona salt diapir, where subsidence has been dramatically exacerbated by mining practices.

Are talus flatiron sequences in Spain climate-controlled landforms?

Summary. This study provides chronological evidence of the influence of climatic variability in the generation of late Quaternary talus flatiron sequences in Spain. The temporal clustering of the OSL and radiocarbon dates obtained from talus flatiron deposits indicates that warm/wet and cold/dry periods controlled the accumulation and incision processes in the slopes, respectively, that led to the development of talus flatirons. These results strongly suggest that talus flatiron sequences constitute valuable paleoclimatic records. Additional and more accurate geochronological data from Spain and other regions of the world would improve the potential of these poorly-known landforms in paleoenvironmental studies.

Landscapes and Landforms of Spain

Spain has a remarkable geomorphological diversity largely due to its geological and climatic variety. From the geological perspective, the Iberian Peninsula may be divided in two broad geological domains; the Iberian Massif in the western sector, and the mountains belts and Cenozoic basins related to Alpine tectonics in the eastern sector. The Iberian Massif (Variscan Spain) mainly consists of Paleozoic metamorphosed sedimentary formations intruded by plutonic rocks. This region is characterised by extensive planation surfaces locally interrupted by inselbergs, and includes outstanding examples of granitic landscapes. The Alpine Mountain Belts, related to the convergence between Europe, the Iberian microplate, and Africa, contain excellent examples of landscapes controlled by active tectonics. In these Alpine orogens, extensive limestone outcrops have favoured the development of outstanding poljes, dolines and karren fields Glacial landscapes are best developed in the Pyrenees, which still contain a number of active cirque glaciers. The Cenozoic Basins include some of the finest areas to examine stunning conglomerate monoliths, dramatic badlands, dune fields, deflation basins associated with lunette dunes and yardangs, and a wide variety of features related to evaporite dissolution. The Canarian Archipelago is a late Cenozoic chain of hot-spot-related volcanic islands located in the Atlantic Ocean west of the Sahara coast. The evolution of the Canaries is characterised by the growth of large volcanic edifices, punctuated by the development of giant landslides. The Teide volcano (3,718 m a.s.l.) in Tenerife rises more than 7 km above the adjacent abyssal plain. A total of 18 eruptions have been documented over the last 500 years, some of them with great societal impact; the 1730-1736 Timanfaya eruption covered more than 20 % of Lanzarote island. The around 10,000 km-long coastline of the Spanish territory display a wide variety of coastal landscapes, including rías, estuaries sequences of raised beaches, deltas, lagoons and spit bars, and dune fields.