Vegetable Oil
Properties keywords: Newtonian liquid, low viscosity, temperature dependent, translucent
Analogue keywords: low viscosity magma, silicate melt, magmatic intrusion
Common names: Vegetaline, olive oil, sunflower oil, coconut oil, canola oil, palm oil
General Information: Vegetable oils are natural materials derived from plants and are commonly used in cooking. All forms share the same basic triglyceride structure, which includes three fatty acid molecules (Harrington, 1986). They are low cost, easy to clean and non-toxic.
Properties
Vegetable oil has a Newtonian rheology and its viscosity shows an Arrhenian dependence on temperature (Figure 1).
The type of vegetable oil used in volcanology experiments is known as Vegetaline and it solidifies at temperatures below 31°C. Above 75°C it is completely molten. At 50°C it has a viscosity of 2 x 10-1 Pas and a liquid density of 890 kg m-3 (Galland et al., 2006; Acocella et al., 2013). As the oil solidifies its volume decreases by 4% (Galland et al., 2006). After heating, the oil will solidify in 15-30 minutes.
Figure 1. a) Stress vs. strain-rate at three temperatures showing Newtonian viscosity of vegetable oil and b) Viscosity against temperature with Arrhenian fit, both from Galland et al. (2006).
It is physically and chemically incompatible with silica flour (a hydrophilic material) and therefore displays limited percolation into this medium (Grout, 1945). The oil has a heat capacity of 1500 J kg-1 K-1 and a thermal conductivity of 0.2 W m-1 K-1 (Galland et al., 2006).
Applications
Vegetable oil has been used predominantly for modelling the intrusion of low viscosity magma into the brittle crust (Galland et al., 2003; 2006; 2007; 2008; 2009; 2014; 2015; Galland, 2005; 2012; Gressier et al., 2010; Norini and Acocella, 2011; Acocella et al., 2013; Chanceaux and Menand, 2014).
Because it solidifies after experiments, intrusions can either be excavated and analysed in 3D (Galland et al., 2009; Galland, 2012), or the entire model can be cut and analysed in-situ (Galland et al., 2003; 2007; 2008). It is typically used with fine grained silica granular materials as the host medium because, due to the high cohesion of silica flour and the fact that it is not wettable by the oil, percolation is reduced and the oil moves instead along fractures, analogous to natural magma behaviour (Galland et al., 2006; 2009). This also allows the oil to form planar sill-like structures (Galland et al., 2007).
Specifically the combination of vegetable oil and silica flour has been used to study the 3D surface displacement related to cone sheet and sill emplacement (Galland, 2012), slope instability on Mount Etna due to shallow dyke intrusions (Acocella et al., 2013), the injection conditions under which injected material produces cone sheets, sills or hybrid intrusions (Galland et al., 2014), and to observe the development of laccoliths without the need for a ductile layer (Galland, 2005).
Experiments by Chanceaux and Menand (2014) injected molten vegetable oil into a gelatine host to observe cooling effects on dyke and sill emplacement. Norini and Acocella (2011) combined low viscosity vegetable oil with high viscosity silicone oil to observe the relationship between intrusion,
Limitations and tips for use
Vegetable oil is very easy to obtain and non-toxic. Care should be taken when heating oil as it can cause burns and is highly flammable.
As an analogue material vegetable oil has some limitations. Due to its very low viscosity it may only be applicable as an analogue for basaltic magma or very shallow crustal intrusions.
It has a single solidification temperature, unlike natural magmas, which transition from liquid to solid in a complex process occurring over a wide range of temperatures (Chanceaux and Menand, 2014).
Lastly, even though vegetable oil will percolate only a small amount into the granular host, this process will still change the pore fluid pressure and should be noted (Gressier et al., 2010).
References
Acocella V, Neri M, and Norini G (2013) An overview of experimental models to understand a complex volcanic instability: Application to Mt Etna, Italy. Journal of Volcanology and Geothermal Research 251: 98-111
Chanceaux L and Menand T (2014) Solidification Effects on Sill Formation: An Experimental Approach. Earth and Planetary Science Letters 10: 79-88
Galland O, de Bremond d’Ars J, Cobbold P R, and Hallot E (2003) Physical models of magmatic intrusion during thrusting. Terra Nova 15: 405-409
Galland O (2005) Interactions mécaniques entre la tectonique compressive et le magmatisme: expériences analogiques et exemple naturel. PhD thesis, Université de Rennes1, Mémoires de Géosciences-Rennes, n°116
Galland O, Cobbold PR, Hallot E, de Bremon d’Ars J, and Delavaud G (2006) Use of vegetable oil and silica powder for scale modeling of magmatic intrusion in a deforming brittle crust. Earth and Planetary Science Letters 243: 786-804
Galland O, Cobbold PR, and de Bremond d’Ars J (2007) Rise and Emplacement of Magma During Horizontal Shortening of the Brittle Crust: Insights from Experimental Modelling. Journal of Geophysical Research 112, B06402
Galland O, Cobbold PR, Hallot E, and de Bremond d’Ars J (2008) Magma-controlled tectonics in compressional settings: insights from geological examples and experimental modelling. Bolletino della Società Geologica Italiana 127(2): 205–208
Galland O, Planke S, Neumann ER, and Malthe-Sørrenssen A (2009) Experimental modelling of shallow magma emplacement: Application to saucer-shaped intrusions. Earth and Planetary Science Letters 277: 373-383
Galland O (2012) Experimental Modelling of Ground Deformation Associated with Shallow Magma Intrusions. Earth and Planetary Science Letters 17: 145-156
Galland O, Burchardt S, Hallot E, Mourgues R, and Bulois C (2014) Dynamics of dikes versus cone sheets in volcanic systems. Journal of Geophysical Research JB011059
Gressier JB, Mourgues R, Bodet L, Matthieu J Y, Galland O, and Cobbold P (2010) Control of pore fluid pressure on depth of emplacement of magmatic sills: An experimental approach, Tectonophysics 489: 1-13
Grout FF (1945) Scale models of structures related to batholiths. American Journal of Science 243A: 260–284
Harrington K (1986) Chemical and Physical Properties of Vegetable Oil Esters and their Effect on Diesel Fuel Performance. BioMass 9: 1-17
Norini G and Acocella V (2011) Analogue Modeling of Flank Instability at Mount Etna: Understanding the Driving Factors. Journal of Geophysical Research 116: B07206