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Constraining the duration of eruptions of the Rangitoto volcano, New Zealand, using paleomagnetism

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Author

  • Linda Aulin

Summary, in English

The volcano Rangitoto belongs to the Auckland volcanic field and is situated north east of Auckland city, New Zealand. The volcanos of the Auckland volcanic field have previously thought to be of monogenetic origin, but recent studies indicate that Rangitoto has a long history of eruptions, which would suggest that the volcanic system may have entered a new phase. The last eruption is dated to 500-550 years BP (1950 AD), however there is little evidence to support the possibility that Rangitoto will not erupt again or that a new volcano on a similar scale will erupt elsewhere in the Auckland area. Reconstruction of past eruptions of the volcano is of great importance to prepare for future volcanic hazards in the area. Two hypotheses of the eruption rate are presented; I) the majority of the eruptions took place within 150 years, ca 650-500 BP, and II) the eruptions were scattered over a period of a few thousand years. To test these hypotheses, paleomagnetic analyses of samples of lava flows from Rangitoto were used to compare variations in the recorded geomagnetic field with models based on regional independently dated paleomagnetic data. Paleointensity experiments were conducted on eight samples of volcanic rocks from Rangitoto according to the Thellier technique. The experiments resulted in two acceptable results and six rejected samples due to multidomain behaviour and thermochemical alteration. The accepted results, combined with additional paleointensity measurements based on an alternating microwave technique as well as independently measured paleomagnetic directions, have been compared to a regional paleomagnetic dataset. I conclude that the data are not sufficient to reject either hypothesis. Further paleomagnetic experiments are suggested.

Publishing year

2017

Language

English

Publication/Series

Dissertations in Geology at Lund University

Document type

Student publication for Bachelor's degree

Topic

  • Earth and Environmental Sciences

Keywords

  • Rangitoto
  • paleomagnetism
  • paleointensity experiments
  • Auckland volcanic field
  • thermal demagnetization

Report number

516

Supervisor

  • Andreas Nilsson
  • Megan Allington

Scientific presentation