Sand volcanoes in the Avon–Heathcote Estuary produced by the 2010–2011 Christchurch Earthquakes: implications for geological preservation and expression

Abstract

Sand volcanoes produced by liquefaction of saturated sands were widespread in the AvonÁHeathcote Estuary following individual major events of the Christchurch 2010Á2011 Earthquake sequence. Sand volcanoes were composed of fine grey sands and varied in diameter over the range 0.2Á5 m, fed by vertical to subvertical feeder pipes of 15Á25 cm diameter that cross-cut mud and shell horizons. Tides and wind-driven waves reduced, and at times removed, the profile of surface features; however, subsurface features remained unaffected. The geological signature of these volcanoes, formed in wet sandy tidally influenced settings such as estuaries, would be preservation of straight-sided feeder pipes 15Á25 cm in diameter, 30 cm in length that cross-cut undeformed strata with or without expression of the erupted cone. Sediments were not able to be excavated beneath the shallow water table, and all observed feeder conduits occurred as roughly cylindrical pipes rather than elongated planar dykes; this does not preclude dykes being present deeper in the subsurface, however. Coseismic subsidence may enhance the preservation potential of surface features by increasing relative water depth, thereby increasing sedimentary accommodation space, and decreasing the influence of wave action in removing cones.

Liquefaction Features Produced by the 2010–2011 Canterbury Earthquake Sequence in Southwest Christchurch, New Zealand, and Preliminary Assessment of Paleoliquefaction Features

“…Sand blows ranged in size from tens of centimeters to meters, and concentrations of sand blows occurred over large areas up to ∼1 km 2 , with a variety of expressions of liquefaction occurring over a wider area of 40 × 20 km 2 (Cubrinovski and Green, 2010; Cubrinovski et al, 2011;Ward et al, 2011;Almond et al, 2012;Kaiser et al, 2012;Reid et al, 2012;Quigley et al, 2013;Bastin et al, 2015;Townsend et al, 2016). As many as 10 distinct liquefaction episodes were reported for a site in Avonside in eastern Christchurch that is underlain by very liquefiable sediment .…”

“…1; Bannister and Gledhill, 2012;Kaiser et al, 2012), produced extensive liquefaction in Christchurch City and the surrounding area (Cubrinovski and Green, 2010;Cubrinovski et al, 2011;Ward et al, 2011;Brackley, 2012;Kaiser et al, 2012;Reid et al, 2012;Bastin et al, 2013Bastin et al, , 2015Quigley et al, 2013;Townsend et al, 2016). Prior to 2010, moderate historical earthquakes had induced liquefaction in the Canterbury region (e.g., the 1901 M w 6.8 Cheviot earthquake; Berrill et al, 1994), and liquefaction susceptibility maps of Christchurch have been available for decades (e.g., Elder et al, 1991, and others; for details, see Brackley, 2012).…”

Paleoliquefaction in Christchurch, New Zealand

“…Surface ejecta commonly manifests as sand blows, blistering of the surface by near-surface sediment injection, and vertical (subsidence) or lateral (lateral spreading) ground deformation (Seed and Idriss, 1982;Sims and Garvin, 1995;Tuttle and Barstow, 1996;Obermeier, 1996;Galli, 2000;Idriss and Boulanger, 2008;Cubrinovski and Green, 2010;Tuttle and Hartleb , 2012;Quigley et al, 2013). Surface liquefaction features may be rapidly (i.e., within hours to months) reworked into forms that are difficult to distinguish from eolian, fluvial, or estuarine deposits (Sims and Garvin, 1995;Reid et al, 2012;Quigley et al, 2013), complicating the geologic identification of prehistoric features. However, subsurface liquefaction features such as dikes, laterally injected sills, and other injection features are commonly present in the geologic record where host sediments are preserved, enabling the detection of historic or prehistoric (i.e., paleoliquefaction) events (Obermeier, 1996;Obermeier et al, 2005;Tuttle et al, 2006).…”

Soft-sediment deformation in a pre-vegetation river system: the Neoproterozoic Torridonian of NW Scotland

“…Fluid escape could have been triggered by earthquakes, with liquefaction developing in a subsurface layer if sediment closer to the surface was unsaturated and had a low liquefaction potential (cf. Reid et al, 2012). However, groundwater movements themselves can generate liquefaction and fluidization, through upwelling groundwater near the toe of an alluvial fan (Williams, 1970), groundwater flow on levees adjacent to active channels (Guhman and Pederson, 1992) or differences in hydraulic head developed during floods (Li et al, 1996).…”