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Syn-eruptive incision of Koko Crater, Oahu, Hawaii by condensed steam and hot cohesive debris flows: a re-interpretation of the type locality of "surge-eroded U-shaped channels"

Bluth, Jessica Keri (2004) Syn-eruptive incision of Koko Crater, Oahu, Hawaii by condensed steam and hot cohesive debris flows: a re-interpretation of the type locality of "surge-eroded U-shaped channels". Master's Thesis, University of Pittsburgh. (Unpublished)

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Phreatomagmatic fall, low-concentration PDC deposits and remobilized equivalents dominate the products of craters (tuff cones/rings) of Koko fissure, south-east Oahu. At Koko crater, Fisher (1977) described "U-shaped" channels, which he interpreted as due to erosion by low-concentration PDCs (surges), with minor modification by stream and debris flows. Similar channels on tuff cones and rings elsewhere in the world have been interpreted as "surge-eroded" by subsequent authors. However, no evidence for erosion by PDCs was observed during recent fieldwork, which suggested rather the following model. An important observation is that initial incision is always correlated with the emplacement of vesiculated ash layers (derived from Hanauma Bay), and is only very rarely associated with other facies. Incision of the vesiculated ash by run-off generated an initial and widespread network of sinuous, narrow (<15 cm) and shallow (<15 cm) rills. The strong correlation of rills with vesiculated ash and the lack of obvious water-escape structures in these ashes implies that run-off was mostly derived from associated steam-rich plumes. Initial steam and rain-fed incision was probably also enhanced in these very fine-grained cohesive deposits as a consequence of lowered infiltration rates. The rill network developed locally into deeper channels (i.e. gullies) during steam and rain-fed run-off, and by significant erosion during emplacement of vesiculated (hot) debris flows, derived from remobilized vesiculated ash. Pyroclastic density currents from Hanuama Bay traveling laterally across the flank of Koko Crater, perpendicular to the gully axes, provided the bulk of the gully fills, but gave rise to little or no modification of their margins. Rill and gully development by rainfall alone could explain similar examples of incision of low-concentration PDC deposits elsewhere in the world, but the possibility of steam-fed rills and erosion by hot debris flows should be considered. Low-concentration PDCs do not seem to be able to erode their substrate in all cases.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Bluth, Jessica
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairSkilling, Ianskilling@pitt.eduSKILLING
Committee MemberJones, Charlescejones@pitt.eduCEJONES
Committee MemberRamsey,
Date: 5 October 2004
Date Type: Completion
Defense Date: 25 June 2004
Approval Date: 5 October 2004
Submission Date: 28 July 2004
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Geology and Planetary Science
Degree: MS - Master of Science
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: Hawaii; incision; Koko Crater; pyroclastic surges; tuff cones; U-shaped channels
Other ID:, etd-07282004-140556
Date Deposited: 10 Nov 2011 19:54
Last Modified: 15 Nov 2016 13:47


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