The nature, origins and distribution of ash aggregates in a large-scale wet eruption deposit: Oruanui, New Zealand

This study documents the processes and products of volcanic ash aggregation in phreatomagmatic phases of the 25.4ka Oruanui supereruption from Taupo volcano, New Zealand. Detailed textural and stratigraphic relationships of aggregates are examined in six of the ten erupted units, which range from re...

Full description

Saved in:
Bibliographic Details
Published in:Journal of volcanology and geothermal research 2013-01, Vol.250, p.129-154
Main Authors: Van Eaton, Alexa R., Wilson, Colin J.N.
Format: Article
Language:English
Subjects:
Accretionary lapilli
Agglomeration
Aggregates
Ash aggregation
Ashes
Crystalline rocks
Density
Deposition
Earth sciences
Earth, ocean, space
Exact sciences and technology
Explosive volcanism
Fallout
Grain size distribution
Igneous and metamorphic rocks petrology, volcanic processes, magmas
Origins
Oruanui eruption
Plume dynamics
Pyroclastic density currents
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:This study documents the processes and products of volcanic ash aggregation in phreatomagmatic phases of the 25.4ka Oruanui supereruption from Taupo volcano, New Zealand. Detailed textural and stratigraphic relationships of aggregates are examined in six of the ten erupted units, which range from relatively dry styles of eruption and deposition (units 2, 5) to mixed (units 6, 7, 8) and dominantly wet (unit 3). Aggregate structures and grain size distributions shift abruptly over vertical scales of cm to dm, providing diagnostic features to identify deposits emplaced primarily as vertical fallout or pyroclastic density currents (PDCs). The six categories of ash aggregates documented here are used to infer distinct volcanic and meteorological interactions in the eruption cloud related to dispersal characteristics and mode of emplacement. Our field observations support the notion of Brown et al. (2010, Origin of accretionary lapilli within ground-hugging density currents: evidence from pyroclastic couplets on Tenerife. Geol. Soc. Am. Bull. 122, 305–320) that deposits bearing matrix-supported accretionary lapilli with concentric internal structure and abundant rim fragments are associated with emplacement of PDCs. However, on the basis of grain size distributions and field relationships, it is inferred that these types of ash aggregates formed their ultrafine ash (dominantly
ISSN:0377-0273
1872-6097
DOI:10.1016/j.jvolgeores.2012.10.016