Ropy pahoehoe: Surface folding of a viscous fluid

Jonathan H. Fink, Raymond Charles Fletcher

Research output: Contribution to journalArticle

106 Scopus citations

Abstract

The regularly spaced surface structure observed on ropy pahoehoe basalt flows may be interpreted as folds which develop at the surface of a fluid whose viscosity decreases with depth. Folds form by the selective amplification of an irregular waviness in surface shape during shortening of the flow surface. The development of a regular fold arc length, predicted by folding theory, is reflected in the length scale of pahoehoe ropes. Pahoehoe fold arc lengths and the strength of the folding instability are determined by: (1) the ratio of the surface viscosity to the interior viscosity; (2) the thickness of the thermal boundary layer across which the viscosity changes; and (3) the ratio of the surface compressive stress to a stress related to the weight of the lava. The braided appearance of many ropy pahoehoe flows can be explained by a superposition of two episodes of folding.

Original languageEnglish (US)
Pages (from-to)151-170
Number of pages20
JournalJournal of Volcanology and Geothermal Research
Volume4
Issue number1-2
DOIs
StatePublished - Jan 1 1978

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

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