Sand

Properties keywords:  solid, granular, low cohesion, plastic

Analogue keywords: brittle crust, unconsolidated sediments and tuffs, gravitational collapse

Common names: Quartz sand, SiO2

General Information:  Sand is a granular material with a grain size between 0.062 and 2 mm in diameter.  It has a diverse composition but its main constituent is SiO2, or quartz.  Sand is readily available, low cost and non-toxic.  It is used in glassmaking, sandblasting and in sand bags as flood defences.

Properties

Dry sand is a very weak material, with negligible cohesion estimated at approximately 12-123 Pa (Schellart et al., 2000; Galland et al., 2015).  This range of cohesion values matches those required to scale with crustal rock, the primary reason sand is the most common rock analogue (Roche et al., 2000; Acocella, 2007).  It also displays a similar Mohr-Coulomb failure criterion to rock, defined by the angle of internal friction, estimated at 30° (Roche et al., 2000; Acocella, 2007).

Its density can range from 1300 – 1700 kg m-3, depending on packing i.e. whether it has been poured or sifted (Callot et al., 2001).  Through sifting it is also possible to achieve a uniform grain size.  Likewise grain sizes can be mixed to obtain a polydisperse mixture.  Sand is permeable, a property that depends on grain size and packing.  It can be fluidized with liquids or gases, when it displays non-Newtonian charateristics.

Sand behaves plastically when deformed, although it can hold some elastic, reversible deformation at low stresses and strains.  A sand edifice will collapse under its own weight along shear planes and fractures, so is useful for showing gravitational collapse (Galland et al., 2015).  Due to its lack of cohesion, sand does not show tensile or mixed mode fracturing, however, small amounts of silica flour may be added to sand to increase cohesion and elastic behaviour and enhance the resolution and details of deformation structures (Donnadieu and Merle, 1998; Merle and Donnadieu, 2000).

Sand can be dyed, making it useful for imaging different strata in the crust.  It can also be saturated with water to enable sectioning of a model post experiment (e.g. Roche et al., 2000).

Applications

Sand is commonly used to simulate the brittle crust in analogue models.  It is most applicable for unconsolidated sediments/tuffs or for showing large-scale tectonic processes of several to tens of km.  This is because material strength decreases relative to the increasing length scale (Corti et al., 2001).

It is often used in conjunction with silicone putty in order to constrain the emplacement of high viscosity magma into the brittle crust.  Several experiments have modelled the effect of inflating or deflating laccolith or stock-like intrusions on fault activation and doming or thinning of the crust (Merle and Vendeville, 1995; Acocella et al., 2000; 2001; 2004; Roche et al., 2000; 2001).

It is also possible to use balloons to simulate sill or laccolith type intrusions (e.g. Walter and Troll, 2001; Kennedy et al., 2004; Lavallee et al., 2004) and study dome subsidence, faulting styles and the influence of topography on caldera shape.  Some studies have combined sand with glycerol to study magma emplacement in tectonic extension (Bonin et al., 2001; Corti et al., 2001).

Figure 1. Examples of analogue experiments from Holohan et al. (2008) showing caldera collapse structures in plan view and cross section.

Limitations and tips for use

As mentioned previously, due to the low cohesion of sand, it only simulates shear faulting and so is not useful for simulating the formation of dykes and sills.  Additionally, when used with silicone as a magma analogue, scaling issues arise whereby the silicone represents magma with a viscosity between 1016 and 1017 Pas, which is far too high to accurately represent natural magmas.  In order to overcome these issues, silica flour can be added to increase the cohesion of sand, and lower viscosity analogues such as syrup or vegetable oil can be used instead of silicone.

Furthermore, as a result of the fairly confined grain size range of sand, scale reduction will inevitably result in a loss of end member grain sizes found in nature (Shea et al., 2008).

When using sand it is important to wash and dry it thoroughly to remove bacteria and a face mask should be worn when sifting fine sand particles.

References

Acocella V, Cifelli R, and Funiciello R (2000) Analogue models of collapse calderas and resurgent domes. Journal of Geophysical Research 104: 81-96

Acocella V, Cifelli F, and Funiciello R (2001) The control of overburden thickness on resurgent domes: insights from analogue models. Journal of Volcanology and Geothermal Research 111 (1–4): 137–153

Acocella V, Funiciello R, Marotta E, Orsi G, and de Vita S (2004) The role of extensional structures on experimental calderas and resurgence. Journal of Volcanology and Geothermal Research 129(1–3): 199–217

Acocella V (2007) Understanding caldera structure and development: An overview of analogue models compared to natural calderas. Earth Science Reviews 85: 125-160

Bonini M, Sokoutis D, Mulugeta G, Boccaletti M, Corti G, Innocenti F, Manetti P, and Mazzarini F (2001) Dynamics of magma emplacement in centrifuge models of continental extension with implications for flank volcanism. Tectonics 20(6): 1053–1065

Byrne PK, Holohan EP, Kervyn M, Van Wyk de Vries B, and Troll VR (2014) Analogue modelling of volcano flank terrace formation on Mars. Geological Society of London Special Publications 401: 185-202

Callot JP, Grigne C, Geoffroy L, and Brun JP (2001) Development of volcanic passive margins: Two-dimensional laboratory models. Tectonics 20: 148-159

Corti G, Bonini M, Innocenti F, Manetti P, and Mulugeta G (2001) Centrifuge models simulating magma emplacement during oblique rifting. Journal of Geodynamics 31:557–576

Donnadieu F and Merle O (1998) Experiments on the indentation process during cryptodome intrusions: new insights into Mount St. Helens deformation. Geology 26(1): 79–82

Galland O, Holohan E, van Wyk de Vries B, and Burchardt S (2015) Laboratory modelling of volcano plumbing systems: a review.  Advances in Volcanology.  Springer Berlin Heidelberg. 1-68

Holohan EP, Troll VR, van Wyk de Vries B, Walsh JJ, and Walter TR (2008) Unzipping Long Valley: an explanation for vent migration patterns during an elliptical ring fracture eruption. Geology 36(4): 323 - 326

Kennedy B, Stix J, Vallance JW, Lavallée Y, and Longpré M-A (2004) Controls on caldera structure: results from analogue sandbox modeling. Geological Society of America Bulletin 116 (5–6): 515–524

Lavallée Y, Stix J, Kennedy B, Richer M, and Longpré M-A (2004) Caldera subsidence in areas of variable topographic relief: results from analogue modeling. Journal of Volcanology and Geothermal Research 129(1–3): 219–236

Merle O and Borgia A (1996) Scaled experiments of volcanic spreading. Journal of Geophysical Research 101: 13805-13817

Merle O and Donnadieu F (2000) Indentation of volcanic edifices by the ascending magma. Geological Society of London Special Publications 174(1): 43–53

Merle O and Vendeville B (1995) Experimental modelling of thin-skinned shortening around magmatic intrusions. Bulletin of Volcanology 57: 33–43

Roche O, Druitt TH, and Merle O (2000) Experimental study of caldera formation. Journal of Geophysical Research 105: 395-416

Roche O, van Wyk de Vries B, and Druitt TH (2001) Sub-surface structures and collapse mechanisms of summit pit craters. Journal of Volcanology and Geothermal Research 105(1– 2): 1–18

Schellart WP (2000) Shear test results for cohesion and friction coefficients for different materials: scaling implications for their usage in analogue modelling. Tectonophysics 324: 1–16

Shea T and van Wyk de Vries B (2008) Structural analysis and analogue modeling of the kinematics and dynamics of rockslide avalanches. Geosphere 4(4): 657

Walter TR and Troll VR (2001) Formation of caldera periphery faults: an experimental study. Bulletin of Volcanology 63: 191–203