Sökning: "Tephra"

Visar resultat 11 - 15 av 15 avhandlingar innehållade ordet Tephra.

1. 11. Late Holocene humidity variability in central Sweden

   Författare :Sofia Andersson; Stefan Wastegård; Gunhild Rosqvist; Kristian Schoning; Frank Chambers; Stockholms universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; humidity change; stable isotopes; Chara spp; Pisidium spp; testate amoebae assemblages; humification; C N ratio; late Holocene; central Sweden; Quaternary geology; Kvartärgeologi; kvartärgeologi; Quarternary Geology;

   Sammanfattning : The aim of this thesis was to reconstruct humidity variability in central Sweden during the late Holocene. A multi-proxy approach was used to infer humidity changes as recorded in a lake and a mire. Age-models were constructed based on radiocarbon dating and the Askja-1875 tephra. LÄS MER

3. 12. Geology of Lagoa das Furnas, a crater lake on São Miguel, Azores archipelago

   Författare :Thommy Andersson; Otto Hermelin; Martin Jakobsson; Alasdair Skelton; Erik Sturkell; Richard Gyllencreutz; Stockholms universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Lagoa das Furnas; Azores; crater lake; geophysical mapping; tephrochronology; volcanic dome; Marine Geology; maringeologi;

   Sammanfattning : In this thesis, the results from a geophysical mapping and coring campaign of Lagoa das Furnas are presented. Specific focus is placed on the origin of a subaqueous volcanic cone mapped in the southern part of the lake. LÄS MER

4. 13. Characterising volcanic magma plumbing systems : A tool to improve eruption forecasting at hazardous volcanoes

   Författare :David A. Budd; Valentin Troll; Tod Waight; Uppsala universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; magma plumbing; oxygen isotopes; thermobarometry; crustal assimilation; Katla; Merapi; Kelud; Toba; volcanic hazards; Geovetenskap med inriktning mot mineralogi; petrologi och tektonik; Earth Science with specialization in Mineral Chemistry; Petrology and Tectonics;

   Sammanfattning : This thesis attempts to develop our understanding of volcanic magma plumbing systems and the magmatic processes that operate within them, such as fractional crystallisation, crustal partial melting, assimilation, and magma mixing. I utilise petrology, rock and mineral geochemistry, and isotope systematics to seek to improve our ability to forecast the eruptive frequency and style of active volcanoes, an aspect often lacking in current volcano monitoring efforts. LÄS MER

5. 14. The Ups and Downs of the Holocene: Exploring Relationships between Global CO2 and Climate Variability in the North Atlantic Region

   Författare :Catherine Jessen; Kvartärgeologi; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; marklära; geomorfologi; climatology; klimatologi; rapid climate change; Holocene climate; atmospheric CO2 concentrations; geochemical proxy indicators; Paleobotanik; palynology; Geology; palynologi; fylogeni; geomorphology; fysisk geografi; Geologi; physical geography; kartografi; pedology; cartography; phylogeny; Palaeobotany; stomatal frequency; lake sediments;

   Sammanfattning : This thesis aimed to examine the relationship between climate and atmospheric CO2 concentrations through rapid climate changes during the Holocene. Climate was reconstructed using high-resolution, radiocarbon dated, lake sediment geochemical proxies (magnetic susceptibility, loss-on-ignition, total carbon/nitrogen/sulphur determinations and biogenic silica), vegetational reconstruction (pollen analysis) and stomatal frequency based CO2 reconstructions. LÄS MER

7. 15. Late Weichselian and early Holocene changes of vegetation, climate and sea level on the Skagi peninsula, northern Iceland

   Författare :Mats Rundgren; Kvartärgeologi; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; asthenosphere viscosity; glacial loading unloading; marine polar front migrations; sea-level change; climate change; vegetation change; Early Holocene; Late Weichselian; Iceland; Lake sediments; Skagi peninsula; Geology; physical geography; Geologi; fysisk geografi;

   Sammanfattning : Sediment sequences from five lakes on the Skagi peninsula, northern Iceland, were subjected to mineral magnetic analysis, carbon analysis, pollen analysis, plant macrofossil analysis, diatom analysis, radiocarbon dating and tephra analysis in order to make detailed reconstructions of vegetation, climate and sea level during the Late Weichselian and Early Holocene. The main purpose was to investigate if the dramatic deglacial climatic shifts recorded in proxy records from the North Atlantic region, such as ice cores, marine sediments and lake sediments, also are registered in Skagi lake sediments, which would be expected considering Iceland´s position in the middle of the North Atlantic Ocean, within the range of the Late Weichselian–Early Holocene migrations of the marine polar front. LÄS MER