Edifice growth and collapse of the Pliocene Mt. Kenya: Evidence of large scale debris avalanches on a high altitude glaciated volcano
Schoorl, J.M. ; Veldkamp, A. ; Claessens, L.F.G. ; Gorp, W. van; Wijbrans, J.R. - \ 2014
Global and Planetary Change 123 (2014)Part A. - ISSN 0921-8181 - p. 44 - 54.
african climate-change - mount kenya - tectonic evolution - gregory rift - east-africa - deposits - geochronology - uplift - pleistocene - himalaya
The cyclic growth and destruction of the Late Cenozoic Stratovolcano Mt. Kenya have been reconstructed for its southeastern segment. At least three major debris avalanche deposits have been reconstructed and dated. The oldest deposits indicate an edifice collapse around 4.9 Ma (40Ar/39Ar), followed by a larger event around 4.1 Ma (40Ar/39Ar). The last and best preserved debris avalanche deposit, with still some morphological expression covering the whole 1214 km2 SE sector, occurred around 2.83 Ma (40Ar/39Ar). This very large debris avalanche event must have truncated the whole top of Mt. Kenya. Of the original typical hummocky relief, only local topographical depressions are still best visible and preserved. Using known geometric empirical parameters of the 3 preserved debris-avalanche deposits, the height of the sector collapse is estimated to be in the range of 5100–6500 m above the current height of 1000 m a.s.l. near the end lobe of the VDA deposits. This demonstrates that Mt. Kenya attained impressive altitudes during its main activity in the Pliocene, being one of the highest mountains in that time and was most probably covered by an ice cap. Correcting for the known net eastward tilting post eruptive uplift of approximately 500 m of the Mt. Kenya summit, our reconstruction indicates that an at least 5.6 to 7 km a.s.l. high active Mt. Kenya existed in the Pliocene landscape between 5.1 and 2.8 Ma. This volcano must have significantly contributed to regional environmental change, by catching rain on its eastern slopes and projecting a rain shadow towards the Kenya Rift valley in the west. The last major edifice collapse event around 2.8 Ma coincides with a major change in regional vegetation. This suggests that the truncating of Mt. Kenya may have caused significant changes in the local climate surrounding Mt. Kenya with possible implications for environmental change in the central Kenya Rift valley, the cradle of hominin evolution.
Fluvial terraces of the northwest Iberian lower Miño River.
Viveen, W. ; Schoorl, J.M. ; Veldkamp, A. ; Balen, R.T. van; Vidal-Romani, J.R. - \ 2013
Journal of Maps 9 (2013)4. - ISSN 1744-5647 - p. 513 - 522.
sea-level change - tectonic activity - portugal - uplift - climate - reconstruction - pleistocene - evolution - incision - deposits
A new fluvial terrace map with a tectonic framework for the northwest Iberian lower Miño River is presented. It is the first integrated map to cover the entire lower, 67-km reach of the Miño River, and to cover both the Spanish and Portuguese side of the river. The map is presented at a scale of 1:200,000, although its features were mapped at a scale of 1:5000. Various map layers can be viewed, such as a digital elevation model (DEM), fluvial sediment thickness layers, a palaeoflow direction layer, a lineament and fault layer, and two terrace and tectonic basin layers, showing up to 10 fluvial terraces and a floodplain level. Interpretation of the map shows that next to regional tectonic uplift and glacioeustacy, local basin subsidence and small-scale block movement are very important for the fluvial network, localised fluvial terrace formation, and preservation.
Fluvial response to Holocene volcanic damming and breaching in the Gediz and Geren rivers, western Turkey
Gorp, W. van; Veldkamp, A. ; Temme, A.J.A.M. ; Maddy, D. ; Demir, T. ; Schriek, T. van der; Reimann, T. ; Wallinga, J. ; Wijbrans, J. ; Schoorl, J.M. - \ 2013
Geomorphology 201 (2013). - ISSN 0169-555X - p. 430 - 448.
pleistocene lava-dam - grand-canyon - luminescence signals - terrace staircase - natural dams - k-feldspars - new-zealand - evolution - arizona - uplift
This study discusses the complex late Holocene evolution of the Gediz River north of Kula, western Turkey, when a basaltic lava flow dammed and filled this river valley. Age control was obtained using established and novel feldspar luminescence techniques on fluvial sands below and on top of the flow. This dating constrained the age of the lava flow to 3.0–2.6 ka. Two damming locations caused by the lava flow have been investigated. The upstream dam caused lake formation and siltation of the upstream Gediz. The downstream dam blocked both the Gediz and a tributary river, the Geren. The associated lake was not silted up because the upstream dam already trapped all the Gediz sediments. Backfillings of the downstream lake are found 1.5 km upstream into the Geren valley. The downstream dam breached first, after which the upstream dam breached creating an outburst flood that imbricated boulders of 10 m3 size and created an epigenetic gorge. The Gediz has lowered its floodplain level at least 15 m since the time of damming, triggering landslides, some of which are active until present. The lower reach of the Geren has experienced fast base level lowering and changed regime from meandering to a straight channel. Complex response to base level change is still ongoing in the Geren and Gediz catchments. These findings are summarized in a diagram conceptualizing lava damming and breaching events. This study demonstrates that one lava flow filling a valley floor can block a river at several locations, leading to different but interrelated fluvial responses of the same river system to the same lava flow.
Volcanic disruption and drainage diversion of the palaeo-Hudut River, a tributary of the Early Pleistocene Gediz River, Western Turkey
Maddy, D. ; Veldkamp, A. ; Jongmans, A.G. ; Candy, I. ; Demir, T. ; Schoorl, J.M. ; Schriek, T. van der; Stemerdink, C. ; Scaife, R.G. ; Gorp, W. van - \ 2012
Geomorphology 165-166 (2012). - ISSN 0169-555X - p. 62 - 77.
se spain - terrace staircase - 2-stage extension - sorbas basin - graben - pliocene - uplift - evolution - capture - gordes
The importance of extrinsic drivers of fluvial system behaviour (climate, tectonics, eustatic sea level) over Quaternary timescales is well documented. However, comparatively fewer studies have been reported concerning the significance of more localised changes at reach to sub-catchment scale, over these extended (10exp4–10exp6 years) timescales. In this paper we examine the Early Pleistocene sedimentary record of the palaeo-Hudut River and compare it with the record from the trunk river into which it drains, the Gediz River of Western Turkey. Both the Gediz River and the Hudut River were subjected to major localised disruption during the Early Pleistocene as a consequence of volcanism but their respective responses to these events appear to differ. Observations are reported from the sedimentary sequence buried beneath the lavas which cap the Burgaz plateau. These sediments record a remarkable amount of detail for a significant period of the Early Pleistocene. These suggest that the palaeo-Hudut system responded largely to the creation and failure of downstream lava dams, both through channel incision and subsequent filling, and via route diversions around lava dams and their associated lakes. In contrast, the Gediz terrace record appears to demonstrate a river which was able to accommodate these changes more readily and hence, continue to undergo sedimentation–incision cycles consistent with a climate forcing.
Mount Kenya volcanic activity and the Late Cenozoic landscape reorganisation in the upper Tana fluvial system
Veldkamp, A. ; Schoorl, J.M. ; Wijbrans, J.R. ; Claessens, L.F.G. - \ 2012
Geomorphology 145-146 (2012). - ISSN 0169-555X - p. 19 - 31.
african climate-change - western turkey - sediment yield - gregory rift - debris flows - east-africa - pleistocene - evolution - river - uplift
Volcanic–fluvial landscape interaction of the late Cenozoic Mt Kenya region in the upper Tana catchment has been reconstructed. The oldest newly dated phonolite flow is 5.78 Ma (40Ar/39Ar), placing the initiation of Mt Kenya volcanic activity within the Late Miocene, much earlier than reported before, 3–3.5 Ma (K/Ar). The main body of the stratovolcano was already in existence around 4.22–5.27 Ma (40Ar/39Ar) supplying lahars to its lower footslopes. The final recorded volcanic main vent phase in the study area produced multiple phonolitic flows and lahars around 2.8 Ma (40Ar/39Ar). There is evidence of at least two major Pliocene drainage blocking events between 3.89 and 2.81 Ma (40Ar/39Ar) causing lava dammed lakes in which volcanic tuff deposits accumulated. Around this time the river Tana did not incise much and shaped an extensive fluvial plain, whose remnants can now be found around 1150 m altitude. This fluvial plain has been incising during the last 2.8 Ma, whereby the incision rate changed in time due to changing uplift rate and volcanic events. A flood basalt eruption covering 1150 km2, estimated to be 5 km3, on the south flank of Mt Kenya of the Thiba basalts at 0.80 Ma (40Ar/39Ar) plugged the Upper Tana basin and caused significant drainage reorganisation. The Tana was diverted southwards abandoning its former valley. The terrace record in the Tana valley downstream the Thiba basalts appears to register this event as a post 0.8 Ma accelerated incision. Current Thiba valley morphology is relatively young and appears to register uplift controlled terraces with interbedded lahars for the last 300 ka only, indicating a delayed fluvial response of approximately 0.5 Ma. The landscape reconstruction demonstrates that the Tana was well able to compensate for many volcanic events such as lahars and lava flows. Only the build-up of a stratovolcano body and a large flood basalt caused prolonged impact on fluvial landscape development
An obliquity-controlled Early Pleistocene river terrace record from Western Turkey?
Maddy, D. ; Demir, T. ; Bridgeland, D. ; Veldkamp, A. ; Stemerdink, C. ; Schriek, T. van der; Westaway, R. - \ 2005
Quaternary Research 63 (2005)3. - ISSN 0033-5894 - p. 339 - 346.
2-stage extension - gediz graben - uplift - stratigraphy - evolution - sequences - selendi - basins - model
Investigation of the Pleistocene sequence of the Gediz River, Western Turkey, has revealed a record of Early Pleistocene river terraces. Eleven terraces spanning the interval from 1.67 to 1.245 million years ago (MIS 59-37) are preserved beneath basaltic lava flows. The high number of terraces over this short time period reflects high-frequency sedimentation/incision cycles preserved due to the fortuitous combination of relatively high uplift rates (0.16 mm yr¿1) and progressive southwards valley migration. Comparison of this record with ODP967 from the Eastern Mediterranean Basin suggests a link between the production of terraces and obliquity-driven 41,000 year climate cycles in the Early Pleistocene.
Late cenozoic landscape development and its tectonic implications for the guadalhorce valley near alora (southern Spain)
Schoorl, J.M. ; Veldkamp, A. - \ 2003
Geomorphology 50 (2003). - ISSN 0169-555X - p. 43 - 57.
landschap - tektoniek - spanje - geomorfologie - zeespiegelschommelingen - kaenozoïcum - geomorphology - landscape - tectonics - spain - sea level fluctuations - kenozoic - se spain - betic cordilleras - terrace stratigraphy - level changes - sorbas basin - late miocene - evolution - uplift - pliopleistocene - chronology
Landscape evolution is the result of a variety of geomorphological processes and their controls in time. In southern Spain tectonics, climate and sea-level fluctuations have been some of the main variables controlling long-term (Late Cenozoic) landscape evolution. In the Guadalhorce valley, Malaga, geomorphological reconstructions can be undertaken using sedimentary evidence from marine and fluvial deposits as well as erosional evidence such as terrain form and longitudinal profile analysis. Data are obtained and analysed from the Upper Miocene to present. These allow reconstructions which add information and constraints to the uplift history and landscape development of the area. Main sedimentation phases are the Late Tortonian, Early Pliocene and Pleistocene. Important erosional hiatus are found for the Middle Miocene, Messinian and Late Pliocene to Early Pleistocene. These phases of erosion and sedimentation resulted in a relative large and elongated Tortonian marine valley filled with complex sedimentary structures. Next, a prolonged stage of erosion of these deposits and incision of the major valley system took place during the Messinian. In the Pliocene, a short palaeo-Guadalhorce, in a narrow and much smaller valley existed. This valley was partly filled with marine sediments and prograding fan delta complexes. During the Pleistocene, a wider and larger incising river system resulted in rearrangements of the drainage network. Evaluating the uplift history of the area, we found that rates of tectonic activity were higher during the Tortonian-Messinian and Upper Pleistocene, while tectonic activity was lower during the Pliocene. Relative uplift rates for the study area range for the Messinian between 160 and 276 in Ma(-1), for the Pliocene between 10 and 15 in Ma and for the Pleistocene between 40 and 100 in Ma(-1) (C) 2002 Elsevier Science B.V All rights reserved.
Reconstructing late quaternary fluvial process controls in the upper aller valley (north Germany) by means of numerical modeling
Veldkamp, A. ; Berg, M. van den; Dijke, J.J. van; Berg van Saparoea, R.M. van den - \ 2002
Netherlands journal of geosciences 81 (2002)3-4. - ISSN 0016-7746 - p. 375 - 388.
geomorfologie - kwartaire afzettingen - tektoniek - terrassen - dalen - simulatiemodellen - geologische sedimentatie - duitsland - rivieren - geomorphology - rivers - geological sedimentation - quaternary deposits - tectonics - terraces - valleys - simulation models - germany - terrace stratigraphy - maas record - europe - uplift - system
The morpho-genetic evolution of the upper Aller valley (Weser basin, North Germany) was reconstructed using geological and geomorphologic data integrated within a numerical process model framework (FLUVER-2). The current relief was shaped by Pre-Elsterian fluvial processes, Elsterian and Saalian ice sheets, followed by Weichselian fluvial processes. Structural analysis based on subsurface data and morphological interpretations were used to reconstruct uplift/subsidence rates. A detailed analysis led to the hypothesis that we are dealing with either a NNW-SSE or a WSW-ENE oriented compression leading to uplift in the upper Aller valley. It is also hypothesised that the NNW-SSE compression might have caused strike-slip deformation leading to differential block movement and tilt.Two different uplift rate scenarios were reconstructed and used as a variable parameter in numerical modelling scenarios simulating the Late Quaternary longitudinal dynamics of the Aller. Each different scenario was run for 150.000 years and calibrated to the actual setting. The resulting model settings were consequently evaluated for their plausibility and validity. Subsequently, regional semi-3D simulations of valley development were made to test the two tectonic stress hypotheses. Differential tectonic uplift and regional tilt seems to have played an important role in shaping the current valley morphology in the upper Aller. Unfortunately, due to the uncertainties involved, we were unable to discriminate between the two postulated tectonic stress scenarios.