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ABSTRACT
Fudge is an excellent analog for basaltic lava and making or tasting fudge leads to memorable lessons on the importance of crystals in controlling the morphology of basaltic lava flows. In particular, students learn why 'a'a flows have rough broken surfaces, while pahoehoe flows are smooth or folded. Furthermore, fudge provides an interesting analog in lessons on the factors that control crystal nucleation and growth as well as how crystals affect magma rheology. Although the full process of making fudge from scratch is too long for a lecture demonstration, fudge can be incorporated into lessons on basalt flows by way of taste-tests, photographs or simplified experiments with pre-made fudge and syrup. Advanced students can run experiments during a laboratory period and examine the crystal textures under a microscope, or do their own experiments in small groups outside of the classroom. Evaluation with written quizzes shows that fudge demonstrations can be an effective aid for teaching the complex concepts of crystal nucleation and growth and their effects on basalt lava flows.
INTRODUCTION
"A close analogy exists in the making of fudge, wherein if the candy is poured or otherwise agitated after crystallization has advanced beyond a certain stage there results a rough, spinose, somewhat granular surface akin to the surface of aa"
Macdonald (1953)
Crystals play a key role in controlling the overall shape, surface textures and flow dynamics of lava flows. However, explaining the kinetics of crystallization and the effect of crystals on lava flow dynamics can be challenging, particularly when opportunities to see lava flows in action are limited. For this reason, we have developed a set of classroom exercises using fudge as an analogue for basaltic lava that allows students to explore the effects of crystallization and shear rate on the dynamics of flow in a safe and fun way. In our experience, this approach not only improves student understanding of lava flow dynamics, but also provides them with basic concepts of crystallization and rheology (flow properties including viscosity) that are broadly applicable to many volcanological problems.
Like lavas, fudge contains crystals, and it is the abundance of sugar crystals that gives fudge its strength and firmness. However, for high quality fudge that feels smooth and creamy in your mouth,...