Benito G.,Institute of Natural Resources |
Rico M.,CSIC - Pyrenean Institute of Ecology |
Sanchez-Moya Y.,Complutense University of Madrid |
Sopena A.,Complutense University of Madrid |
And 2 more authors.
Global and Planetary Change | Year: 2010
The Guadalentín River, located in southeast Spain, is considered one of the most torrential rivers in Spain, as indicated by catastrophic events such as the 1879 flood that caused 777 fatalities in the Murcia region. In this paper, flood frequency and magnitude of the upper Guadalentín River were reconstructed using geomorphological evidence, combined with one-dimensional hydraulic modelling and supported by records from documentary sources at Lorca in the lower Guadalentín catchment. Palaeoflood studies were conducted along a 2.5-km reach located at the confluence of the Rambla Mayor (162 km2) and Caramel River (210 km2). These tributaries join at the entrance of a narrow bedrock canyon, carved in Cretaceous limestone, which is 15-30 m wide and 40 m deep. Six stratigraphic profiles were described, the thickest and most complete corresponding to flood benches deposited upstream of the canyon constriction. The stratigraphic and documentary records identify five main phases of increased flood frequency. Phase 1, based on sedimentary palaeoflood evidence alone, occurred at c. AD 950-1200 with at least ten floods with minimum discharge estimates of 15-580 m3 s- 1. Phases 2-5, identified through combined sedimentary and documentary evidence occurred at: (a) AD 1648-1672, with eight documentary floods and two palaeofloods exceeding 580-680 m3 s- 1 (most probably the AD 1651 and 1653 events); (b) AD 1769-1802, comprising seven documentary floods, of which at least two events (> 250 m3 s- 1) are preserved in the sedimentary record; (c) AD 1830-1840, with four documentary floods, and at least two events recorded in the stratigraphy (760-1035 m3 s- 1); and finally (d) the AD 1877-1900 period that witnessed seven documentary floods, with three palaeofloods exceeding 880 m3 s- 1. The palaeoflood and historical flood information indicate an anomalous increase in the frequency of large magnitude floods between AD 1830 and 1900, which can be attributed to climatic variability accentuated by intensive deforestation and land use practices during the first decades of the nineteenth century. © 2009.
Letty B.,Institute of Natural Resources |
Alcock R.,Mdukatshani Rural Development Trust
African Journal of Range and Forage Science | Year: 2013
This paper was prepared in response to a paper prepared by Vetter (in this issue) that addressed the issue of policy development related to sustainable management of rangelands. In line with the sentiments of Vetter, policies are understood to guide the allocation of resources. The important contribution that livestock make to rural livelihoods is well recognised and strengthening crop-livestock interactions is seen as an effective way of improving livestock productivity while generally being understood as an effective way to increase agricultural production so as to meet the growing needs of the global population. The use of crop residues by livestock is one specific linkage that offers opportunities, but this could be maximised by increasing the yield and quality of the residues. One key challenge to strengthening crop-livestock interactions is the extent to which arable lands are being abandoned. Efforts need to be made to reverse this situation, which requires a range of technical and social/institutional interventions. Although some policy documents refer to integrated systems and alternative cropping practices, there is limited evidence that this in fact is happening on the ground. Policy needs to support crop-livestock interactions more actively so that on-farm research with farmers, as is happening in Msinga, becomes more widespread. © 2013 Copyright NISC (Pty) Ltd.
Gerber T.P.,Duke University |
Pratson L.F.,Duke University |
Kuehl S.,Virginia Institute of Marine Science |
Walsh J.P.,East Carolina University |
And 2 more authors.
Marine Geology | Year: 2010
We present geophysical and core evidence showing how subsidence caused by forearc shortening has accommodated Late Pleistocene and Holocene sediments supplied to the tectonically active Waipaoa shelf (NZ), limiting off-shelf export during the early sea level highstand. The last glacioeustatic fall and subsequent rise exposed and then flooded a shelf segmented into subbasins separated by zones of uplift, leaving key stratigraphic markers of shoreline regression and transgression that vary strongly in character across the shelf. Highstand sediment isopachs tied to piston cores dated using tephra correlation and a radiocarbon age model provide a sediment budget at ∼ 2000 yr intervals from the mid-Holocene (∼ 5500 cal. yr BP) to present. Sediment load estimates from our shelf budget are in agreement with published model estimates for suspended sediment discharge from the Waipaoa River for the past 3000 yr but, importantly, do not show the 6-fold increase in the Waipaoa's sediment output that began with human settlement 700 yr ago and accelerated with deforestation over the last century. Bypassing of Waipaoa sediment to the slope may therefore be a recent phenomenon caused by unnaturally high sediment loads, a conclusion supported by data reported elsewhere in this volume. Our study also reveals evidence for (1) a relatively thick mid-shelf transgressive section deposited during the last eustatic rise that may correlate to estuarine sequences reported from numerous sites on the modern coastline of the North Island, (2) a slight decrease in total basin filling rates during the highstand, and (3) variability in the partitioning of highstand sediments between individual subbasins that may reflect differing degrees of tectonic accommodation. © 2009 Elsevier B.V. All rights reserved.
Nemeth K.,Institute of Natural Resources
Special Paper of the Geological Society of America | Year: 2010
Monogenetic volcanism is commonly represented by evolution of clusters of individual volcanoes. Whereas the eruption duration of an individual volcano of a volcanic field is generally short, the life of the entire volcanic field is longer than that of a composite volcano (e.g., stratovolcano). The magmatic output of an individual center in a volcanic field is 1-3 orders of magnitude less than that of a composite volcano, although the total field may be of the same volume as a composite volcano in any composition. These features suggest that the magma source feeding both monogenetic volcanic fields and composite volcanoes are in the same range. Monogenetic volcanic fields therefore are an important and enigmatic manifestation of magmatism at the Earth's surface. The long eruption duration for an entire volcanic field makes this type of volcanism important for understanding sedimentary basin evolution. Accumulated eruptive products may not be significant from a single volcano, but the collective field may contribute significant sediment to a basin. The eruptive history of volcanic fields may span millions of years, during which dramatic climatic and paleoenvironmental changes can take place. Through systematic study of individual volcanoes in a field, detailed paleoenvironmental reconstructions can be made as well as paleogeographic evaluations and erosion-rate estimates. Monogenetic volcanoes are typically considered to erupt only once and to be short-lived; recent studies, however, demonstrate that the general architecture of a monogenetic volcano can be very complex and exhibit longer eruption durations than expected. In this way, monogenetic volcanic fields should be viewed as a complex, longlasting volcanism that in many respects carries the basic characteristics similar to those known from composite volcanoes. © 2010 The Geological Society of America. All rights reserved.
Benito G.,Institute of Natural Resources |
Sancho C.,University of Zaragoza |
Pena J.L.,University of Zaragoza |
Machado M.J.,Institute of Natural Resources |
Rhodes E.J.,University of California at Los Angeles
Quaternary Science Reviews | Year: 2010
Fluvial systems crossing evaporitic bedrock are commonly affected by karstic subsidence, which may result in river adjustments recorded by anomalous alluvial thickening. A remarkable study case is the Gállego River, at the Central Ebro Basin (NE Spain), where dissolution of evaporite bedrock gave rise to a subsidence induced depositional basin 30 km-long by 8 km-wide, infilled with alluvial sediments in excess of 110 m in thickness. A detailed morpho-sedimentary analysis of alluvial deposits supported with optically stimulated luminescence dating has revealed that paleokarst subsidence and accelerated fluvial aggradation occurred during discrete time periods, the most recent one being at 140-155 kyr (end of MIS 6). Subsequent alluvial terrace formation occurred at ∼110 kyr, 63-48 kyr and ∼17 kyr, linked to fluvio-glacial activity at the Pyrenean headwaters. Large-scale bedrock dissolution and associated alluviation appear to be sensitive to 1) long lasting periods of glacial outwash discharges; 2) high effective runoff from the extensive valley slopes, and 3) increased surface-groundwater exchange and groundwater circulation. The last large-scale subsidence episode (140-155 kyr) correlates with hydrological proxies reflecting a prolonged (141-149 kyr) salinity drop in the western Mediterranean, previously interpreted as linked to a Heinrich event, but which may instead represent an anomalous period of enhanced river discharge fed by extensively glaciated mountains. © 2010 Elsevier Ltd.