Spreading and sagging are two long-recognized modes of basement-controlled deformation at volcanoes. Recent analogue experiments have identified a continuum-like transition between such deformation modes. One challenge has been to find objective criteria for distinguishing between the end-member modes of deformation (spreading or sagging) and any transitional modes. To address these issues, we conducted scaled analogue experiments involving a sand-plaster cone emplaced upon a basement that comprised an upper brittle layer and a lower ductile layer. Horizontal deformation and displacement fields were quantified by Digital Image Correlation (DIC) analysis of time-lapse images. We find that cones spread, sag, or display mixed styles, depending on the ratios of ductile (D) or brittle (B) layer thickness to cone height (H). While these behaviors comprise a continuum structurally, there is a clear distinction between end-member and transitional behaviors in terms of horizontal displacement patterns. Spreading and sagging behaviors are characterized by maximum displacement vectors directed radially away from or toward the volcano summit, respectively. The transitional ‘spragging’ phase generally shows both inward and outward directed displacements, but the maximum displacement is always directed outward and located in the basement. These objective criteria for deformation mode classification enable the geometric control from the basement properties to be quantitatively expressed in dimensionless B/H vs. D/H space. Our new, comprehensive quantification of how basement properties may control the structural architecture of volcanoes is validated by data from several cases in nature.
|Title of host publication||26th IUGG General Assembly 2015|
|Place of Publication||Prague|
|Publication status||Published - 22 Jun 2015|
|Event||IUGG 2015 - , United Kingdom|
Duration: 22 Jun 2015 → 2 Jul 2015
|Period||22/06/15 → 2/07/15|