TY - THES

T1 - Magnetism of postglacial lavas from Snæfells volcano, Iceland: Field reconstruction and archeomagnetic dating

AU - Tauber, Elisabeth

N1 - embargoed until null

PY - 2011

Y1 - 2011

N2 - Recent volcanic eruptions in Iceland demonstrate the importance of assessing volcanogenic hazards. Individual volcanic events occur on average at 5-year intervals while larger eruptions could occur in cycles of 500 – 1000 years. The determination of historic eruptions, calculation of the frequency of past eruptions, the definitions of eruption cycles and of all volcanic processes that may occur are essential for assessing volcanogenic risks. Paleomagnetic investigations are ideal contributions for determining the age of historical lava flows as wells as defining eruption cycles. The advantage of this method is that dating is conducted lava flow itself. Other methods often use secondary sources, e.g. the dating of organic material from tephra layers of which the origin is often ambiguous. Samples from fourteen different lava flows were taken from the Snæfells peninsula in west Iceland. All sampled sites correspond to post-glacial holocene lava flows, related to volcanic activity at Snæfells. The samples were subjected to paleomagnetic and rock magnetic analyses in order to obtain reliable intensities and directions of the ancient magnetic field. Curie-temperatures, measurements of anisotropy of magnetic susceptibility (AMS) and thermally dependent anhysteretic remanent magnetization (ARM) measurements are used to proof the reliability of paleomagnetic information and furthermore to subdivide the samples into specific groups regarding alteration and mineralogy. Paleodirection results yield average inclinations between 54° and 82° and declinations between 290° and 45°, as expected for the high northern latitude. According to rock magnetic results and the classification into alteration- and mineralogy-types, a pre-selection for further paleomagnetic measurements was conducted. Thirty-eight samples were chosen for a modified Thellier-type paleointensity determination, which includes alteration checks and domain state checks. The results allow the estimation of the previously unknown ages of the Holocene flows in the vicinity of Snæfells For this purpose, the paleomagnetic directions were compared to inclination, declination and also to field intensity by using a Bayesian archeomagnetic dating approach. Two of the investigated lava flows correlate and confirm existing age determination of tephra layers. It was possible to relate one flow, which was previously correlated to an older event, to an eruption that occurred 1000 years later. Three of the determined lava flows are dated with more than 4500 years BP. Furthermore an additional event occurring 2770 years BP was identified.

AB - Recent volcanic eruptions in Iceland demonstrate the importance of assessing volcanogenic hazards. Individual volcanic events occur on average at 5-year intervals while larger eruptions could occur in cycles of 500 – 1000 years. The determination of historic eruptions, calculation of the frequency of past eruptions, the definitions of eruption cycles and of all volcanic processes that may occur are essential for assessing volcanogenic risks. Paleomagnetic investigations are ideal contributions for determining the age of historical lava flows as wells as defining eruption cycles. The advantage of this method is that dating is conducted lava flow itself. Other methods often use secondary sources, e.g. the dating of organic material from tephra layers of which the origin is often ambiguous. Samples from fourteen different lava flows were taken from the Snæfells peninsula in west Iceland. All sampled sites correspond to post-glacial holocene lava flows, related to volcanic activity at Snæfells. The samples were subjected to paleomagnetic and rock magnetic analyses in order to obtain reliable intensities and directions of the ancient magnetic field. Curie-temperatures, measurements of anisotropy of magnetic susceptibility (AMS) and thermally dependent anhysteretic remanent magnetization (ARM) measurements are used to proof the reliability of paleomagnetic information and furthermore to subdivide the samples into specific groups regarding alteration and mineralogy. Paleodirection results yield average inclinations between 54° and 82° and declinations between 290° and 45°, as expected for the high northern latitude. According to rock magnetic results and the classification into alteration- and mineralogy-types, a pre-selection for further paleomagnetic measurements was conducted. Thirty-eight samples were chosen for a modified Thellier-type paleointensity determination, which includes alteration checks and domain state checks. The results allow the estimation of the previously unknown ages of the Holocene flows in the vicinity of Snæfells For this purpose, the paleomagnetic directions were compared to inclination, declination and also to field intensity by using a Bayesian archeomagnetic dating approach. Two of the investigated lava flows correlate and confirm existing age determination of tephra layers. It was possible to relate one flow, which was previously correlated to an older event, to an eruption that occurred 1000 years later. Three of the determined lava flows are dated with more than 4500 years BP. Furthermore an additional event occurring 2770 years BP was identified.

KW - geophysics

KW - paleomagnetism

KW - dating

KW - Thellier

KW - Geophysik

KW - Paläomagnetismus

KW - Altersdatierung

KW - Thellier

M3 - Master's Thesis

ER -