Lyell Collection
Journal of the Geological Society
Lyell Centre  |   Lyell Collection  |   Subscriptions   |   Geological Society  |   Email alerts  |   Online bookshop  |   Help

Keywords:
Author:
Advanced search>>
This Article
Right arrow Figures Only
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Web of Science (10)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by KOKELAAR, P.
Right arrow Articles by KÖNIGER, S.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation
Journal of the Geological Society; 2000; v. 157; issue.3; p. 517-536
© 2000 Geological Society of London

Regular Article

Marine emplacement of welded ignimbrite: the Ordovician Pitts Head Tuff, North Wales

PETER KOKELAAR1 & STEPHAN KÖNIGER2

1 Earth Sciences Department, Liverpool University, Liverpool L69 3BX, UK (e-mail: p.kokelaar{at}liv.ac.uk)
2 Institut für Geologie, Universität Würzburg, Pleicherwall 1, D-97070 Würzburg, Germany

Scientific editing by Jennie Gilbert.

The Pitts Head welded ignimbrite records a subaerial, large-volume eruption and associated pyroclastic current that flowed into the sea. The current 15 km from source was steadily sustained with high mass flux and high particle concentration towards its base, and it entered the sea without substantial mixing with water and thus without large-scale hydroexplosivity and without general cooling. It continued to aggrade ignimbrite at >580°C for at least 3–4 km from the original shoreline, in water initially ≥50 m deep. Entirely subaqueous, hot-state, progressive aggradation and welding of the ignimbrite occurred where the water could not be wholly displaced by the current, although eventually the deposit displaced the shore >4 km seawards. Wet sea-floor sediments buried by the ignimbrite were heated and locally fluidized by steam, and several square kilometres of hot ignimbrite with variable thicknesses of sedimentary substrate detached and slid downslope. Directions of sliding and the order of piling-up of slide sheets are shown by hot-state (rheomorphic) deformation fabrics and the geometric relations of detachment surfaces. Extensional disruption of the ignimbrite is marked by breaks in the sheet via which fluidized sediments were mobilized, locally to form rootless vents. Both the initial incursion of the pyroclastic current into the sea and the subsequent submarine sliding of the ignimbrite are likely to have caused tsunamis. Similar occurrences at modern coastlines presently susceptible to incursion of high mass flux pyroclastic currents (e.g. Taupo Volcanic Zone, New Zealand; Neapolitan region, Italy; vicinity of Manila (Taal), Philippines) would, according to tsunami propagation behaviour, cause significant near-and far-field coastal hazard.


Keywords: density currents, ignimbrite, submarine volcanoes, fluidization, tsunami.




This article has been cited by other articles:


Home page
 Journal of the Geological SocietyHome page
A. MILIA, F. MOLISSO, A. RASPINI, M. SACCHI, and M. M. TORRENTE
Syneruptive features and sedimentary processes associated with pyroclastic currents entering the sea: the AD 79 eruption of Vesuvius, Bay of Naples, Italy
Journal of the Geological Society, 2008; 165: 839 - 848.
[Abstract] [Full Text] [PDF]

Home page
 Geological Society, London, MemoirsHome page
References
Geological Society, London, Memoirs, 2003; 27: 127 - 136.
[PDF]