A 4000-year debris flow record based on amphibious investigations of fan delta activity in Plansee (Austria, Eastern Alps)

<p>The frequency of debris flows is hypothesized to have increased in recent decades with enhanced rainstorm activity. Geological evidence to test the relationship between climate and debris flow activity for prehistoric times is scarce due to incomplete sediment records, complex stratigraphy,...

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Autores principales:	C. Kiefer, P. Oswald, J. Moernaut, S. C. Fabbri, C. Mayr, M. Strasser, M. Krautblatter
Formato:	article
Lenguaje:	EN
Publicado:	Copernicus Publications 2021
Materias:	Dynamic and structural geology QE500-639.5
Acceso en línea:	https://doaj.org/article/80cc8c7c6b8d49ce96a0346fd82a2f99
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id	oai:doaj.org-article:80cc8c7c6b8d49ce96a0346fd82a2f99
record_format	dspace
institution	DOAJ
collection	DOAJ
language	EN
topic	Dynamic and structural geology QE500-639.5
spellingShingle	Dynamic and structural geology QE500-639.5 C. Kiefer P. Oswald J. Moernaut S. C. Fabbri S. C. Fabbri C. Mayr M. Strasser M. Krautblatter A 4000-year debris flow record based on amphibious investigations of fan delta activity in Plansee (Austria, Eastern Alps)
description	<p>The frequency of debris flows is hypothesized to have increased in recent decades with enhanced rainstorm activity. Geological evidence to test the relationship between climate and debris flow activity for prehistoric times is scarce due to incomplete sediment records, complex stratigraphy, and insufficient age control, especially in Alpine environments. In lacustrine archives, the link between onshore debris flow processes and the sedimentary record in lakes is poorly investigated. We present an amphibious characterization of alluvial fan deltas and a continuous 4000-year debris flow record from Plansee (Tyrol, Austria), combining light detection and ranging (lidar) data, swath bathymetry, and sediment core analyses. The geomorphic investigation of two fan deltas in different developmental stages revealed an evolutionary pattern of backfilling and new channel formation onshore, together with active subaqueous progradation on a juvenile fan delta, major onshore sediment deposition, and only few, but larger, subaqueous deposits on a mature fan delta. Geomorphic evidence for stacked and braided debris flow lobes, subaquatic landslide deposits, and different types of turbidites in sediment cores facilitated a process-based event identification, i.e. distinguishing between debris-flow-induced or earthquake-induced turbidites throughout the 4000-year sedimentary record. We directly correlate subaqueous lobe-shaped deposits with high backscatter signals to terrestrial debris flow activity of the last century. Moreover, turbidite thickness distribution along a transect of four cores allows us to pinpoint numerous events as being related to debris flow activity on a juvenile fan delta. In the sediment core, debris-flow-induced turbidites feature a more gradual fining upward grain size trend and higher TOC (total organic carbon) and <span class="inline-formula"><i>δ</i></span><span class="inline-formula"><sup>13</sup>C</span> values compared to earthquake-induced turbidites. The 4000-year event record contains 138 debris-flow-induced turbidites separated into four phases of similar debris flow activity (df phases). df phase 1 (<span class="inline-formula">∼2120</span> to <span class="inline-formula">∼2040</span> before the common era – BCE) reflects the second-highest observed event frequencies and is interpreted as being a postseismic landscape response. After a long period of long recurrence intervals without any outstanding increases in debris flow activity during df phase 2 (<span class="inline-formula">∼2040</span> BCE to <span class="inline-formula">∼1520</span> common era – CE), there are slightly increased event frequencies in df phase 3 (<span class="inline-formula">∼1520</span> to <span class="inline-formula">∼1920</span> CE). df phase 4 (<span class="inline-formula">∼1920</span> to 2018 CE) exhibits a drastic increase in debris flow activity, followed by the overall highest debris flow frequency of the whole record, which is about 7 times higher than during df phase 3. We show that the frequency increase in the debris-flow-induced turbidite<span id="page1482"/> record matches a previously postulated increase in debris flow events derived from aerial photography at Plansee in the last century. The triggering of debris flows is more controlled by short, intense precipitation than any other mass movement process, and we demonstrate that lacustrine debris flow records provide a unique inventory of hazard-relevant rainstorm frequencies over decades, centuries, and millennia. The presented increase in debris flow frequency since the start of the 20th century coincides with a twofold enhanced rainstorm activity in the Northern European Alps and, therefore, provides a novel technique for the systematic understanding of non-stationary debris flow frequencies in a changing climate.</p>
format	article
author	C. Kiefer P. Oswald J. Moernaut S. C. Fabbri S. C. Fabbri C. Mayr M. Strasser M. Krautblatter
author_facet	C. Kiefer P. Oswald J. Moernaut S. C. Fabbri S. C. Fabbri C. Mayr M. Strasser M. Krautblatter
author_sort	C. Kiefer
title	A 4000-year debris flow record based on amphibious investigations of fan delta activity in Plansee (Austria, Eastern Alps)
title_short	A 4000-year debris flow record based on amphibious investigations of fan delta activity in Plansee (Austria, Eastern Alps)
title_full	A 4000-year debris flow record based on amphibious investigations of fan delta activity in Plansee (Austria, Eastern Alps)
title_fullStr	A 4000-year debris flow record based on amphibious investigations of fan delta activity in Plansee (Austria, Eastern Alps)
title_full_unstemmed	A 4000-year debris flow record based on amphibious investigations of fan delta activity in Plansee (Austria, Eastern Alps)
title_sort	4000-year debris flow record based on amphibious investigations of fan delta activity in plansee (austria, eastern alps)
publisher	Copernicus Publications
publishDate	2021
url	https://doaj.org/article/80cc8c7c6b8d49ce96a0346fd82a2f99
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spelling	oai:doaj.org-article:80cc8c7c6b8d49ce96a0346fd82a2f992021-11-29T07:20:29ZA 4000-year debris flow record based on amphibious investigations of fan delta activity in Plansee (Austria, Eastern Alps)10.5194/esurf-9-1481-20212196-63112196-632Xhttps://doaj.org/article/80cc8c7c6b8d49ce96a0346fd82a2f992021-11-01T00:00:00Zhttps://esurf.copernicus.org/articles/9/1481/2021/esurf-9-1481-2021.pdfhttps://doaj.org/toc/2196-6311https://doaj.org/toc/2196-632X<p>The frequency of debris flows is hypothesized to have increased in recent decades with enhanced rainstorm activity. Geological evidence to test the relationship between climate and debris flow activity for prehistoric times is scarce due to incomplete sediment records, complex stratigraphy, and insufficient age control, especially in Alpine environments. In lacustrine archives, the link between onshore debris flow processes and the sedimentary record in lakes is poorly investigated. We present an amphibious characterization of alluvial fan deltas and a continuous 4000-year debris flow record from Plansee (Tyrol, Austria), combining light detection and ranging (lidar) data, swath bathymetry, and sediment core analyses. The geomorphic investigation of two fan deltas in different developmental stages revealed an evolutionary pattern of backfilling and new channel formation onshore, together with active subaqueous progradation on a juvenile fan delta, major onshore sediment deposition, and only few, but larger, subaqueous deposits on a mature fan delta. Geomorphic evidence for stacked and braided debris flow lobes, subaquatic landslide deposits, and different types of turbidites in sediment cores facilitated a process-based event identification, i.e. distinguishing between debris-flow-induced or earthquake-induced turbidites throughout the 4000-year sedimentary record. We directly correlate subaqueous lobe-shaped deposits with high backscatter signals to terrestrial debris flow activity of the last century. Moreover, turbidite thickness distribution along a transect of four cores allows us to pinpoint numerous events as being related to debris flow activity on a juvenile fan delta. In the sediment core, debris-flow-induced turbidites feature a more gradual fining upward grain size trend and higher TOC (total organic carbon) and <span class="inline-formula"><i>δ</i></span><span class="inline-formula"><sup>13</sup>C</span> values compared to earthquake-induced turbidites. The 4000-year event record contains 138 debris-flow-induced turbidites separated into four phases of similar debris flow activity (df phases). df phase 1 (<span class="inline-formula">∼2120</span> to <span class="inline-formula">∼2040</span> before the common era – BCE) reflects the second-highest observed event frequencies and is interpreted as being a postseismic landscape response. After a long period of long recurrence intervals without any outstanding increases in debris flow activity during df phase 2 (<span class="inline-formula">∼2040</span> BCE to <span class="inline-formula">∼1520</span> common era – CE), there are slightly increased event frequencies in df phase 3 (<span class="inline-formula">∼1520</span> to <span class="inline-formula">∼1920</span> CE). df phase 4 (<span class="inline-formula">∼1920</span> to 2018 CE) exhibits a drastic increase in debris flow activity, followed by the overall highest debris flow frequency of the whole record, which is about 7 times higher than during df phase 3. We show that the frequency increase in the debris-flow-induced turbidite<span id="page1482"/> record matches a previously postulated increase in debris flow events derived from aerial photography at Plansee in the last century. The triggering of debris flows is more controlled by short, intense precipitation than any other mass movement process, and we demonstrate that lacustrine debris flow records provide a unique inventory of hazard-relevant rainstorm frequencies over decades, centuries, and millennia. The presented increase in debris flow frequency since the start of the 20th century coincides with a twofold enhanced rainstorm activity in the Northern European Alps and, therefore, provides a novel technique for the systematic understanding of non-stationary debris flow frequencies in a changing climate.</p>C. KieferP. OswaldJ. MoernautS. C. FabbriS. C. FabbriC. MayrM. StrasserM. KrautblatterCopernicus PublicationsarticleDynamic and structural geologyQE500-639.5ENEarth Surface Dynamics, Vol 9, Pp 1481-1503 (2021)

A 4000-year debris flow record based on amphibious investigations of fan delta activity in Plansee (Austria, Eastern Alps)

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