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By Rosie Flanagan
“The relation between what we see and what we know is never settled. Each evening we see the sun set. We know that the earth is turning away from it. Yet the knowledge, the explanation, never quite fits the sight.”
– John Berger, Ways of Seeing 
I was born beneath a mountain that I know to be blue. I grew up in a house that stands on the edge of its foothills, overlooking a river that winds past Hobart on its journey to the Southern Ocean. The watchful presence of kunanyi/Mount Wellington is a defining feature of the place that I call home.
This mountain sings a different blue each season. During summer, its shape is uncertain and its edges evanescent. In the heat it becomes a cerulean haze that merges with the sky. This diaphanous veil lifts in autumn, revealing a landscape that is deep-blue, and dolerite columns that I have seen verge on violet. When the weather is crisp, the mountain’s face can appear pale and severe; the color of an early bruise masked by mist. Its summit dusted white.
When I began writing this piece, I emailed my father about this blue-ness. Despite having lived for many years in and out of the mountain’s inky shadow, the reality of its color was something that I had never considered. Was it because of the trees, I asked. He replied, “A good question: Mount Wellington’s dominant tree form is eucalyptus, though there are many other tree and shrub species. And then there is a lot of bare rock, screes, cliffs and so on. But from a distance everything, without exception, is simply a hue of blue.”
Mountains appear blue for the same reason that the sky appears blue: As light waves hit the earth’s atmosphere, the high-frequency blue light waves interact with the molecules in the air, and scatter light in all directions. Mountains, being a source of darkness as opposed to a source of light like the sun, reflect little light to our eyes. So when looking at them, we perceive instead the light from the sun that is scattered between us and the mountain – causing them to appear blue when viewed from far away. The further from the mountain we are, the lighter the blue it will appear.
But kunanyi/Mount Wellington is not simply stained with blue by distance. On days when heat rises from the tarmac in the city, its outline seems to shift and shimmer: as if the color of its constitution is attempting escape.
Tasmania is home to 28 species of eucalyptus, a genus of flowering trees, shrubs and mallees from the myrtle family, which is largely native to Australia. Among the various microclimates of kunanyi/Mount Wellington, 12 species of eucalyptus can be found: snow gums in the subalpine woodlands, blue gums in areas of dry sclerophyll, and white, yellow, blue and stringybarks in areas considered wet or rainforest-like. Because of the large swathes of eucalyptus on the mountain, bush walks there are usually accompanied by the scent of their leaves.
Packages from my best friend in Hobart often include a stem of (undeclared) eucalyptus, I find the pale scent and form of these dried leaves incredibly comforting. If you look closely at them, you can see tiny round dots that surround their network of veins. These dots are glands, they hold two compounds: monoterpene and sesquiterpene – eucalyptus oil. The molecule isoprene, a volatile liquid hydrocarbon, forms part of both of these compounds.
During short, acute temperature changes – an increasingly common phenomenon in a period of climate crisis – the production and emission of isoprene by eucalyptus can rise dramatically. “Above a critical temperature some plants release up to 50% of the photosynthetically assimilated carbon into the atmosphere in the form of isoprenoids [monoterpenes and isoprene]”, a molecular dynamics study from 2006 explains.
Synthesis of isoprene is dependent on seasons, with emissions highest in summer and lowest in winter. Similarly, leaves at the crown of trees produce more of the molecule because they are consistently exposed to sunlight. Emission rates are highest during the day and tend to decline as the sun goes down. When isoprenoids are released into the atmosphere, their microscopic particles cause a scattering of light that appears blue. During extreme temperatures, the amount of isoprenoids emitted by plants can be substantial enough to visually filter sunlight, casting what appears – from a distance – to be a blue glow around their edges.
This phenomenon has been documented in places with large belts of contiguous forest with high numbers of isoprene-rich plants – like the Blue Mountains in New South Wales (eucalyptus), and the Blue Ridge Mountains in North Western Carolina (oaks). It may be responsible for the sfumato outline that I recall kunanyi/Mount Wellington having in the heat. Or, it may not. It has been four years since I spent a summer in Tasmania, so I cannot say whether the edges of the mountain smudge beneath sun – or if they ever really did. Perhaps it is as simple as acknowledging that I, like many writers before me, have fallen in love with a color that is best viewed from a distance.
Rosie Flanagan is a Berlin-based writer and editor.
1. John Berger, Ways of Seeing (London: Penguin, 1987), 7.2. Magdalena Siwko et al., “Does isoprene protect plant membranes from thermal shock? A molecular dynamics study,” Biochimica et Biophysica Acta (BBA) - Biomembranes 1768, no. 2 (2007): 198. https://doi.org/10.1016/j.bbamem.2006.09.0233. Csiro Australia, “Trees And Air Pollution,” ScienceDaily. www.sciencedaily.com/releases/2001/01/010109223032.htm (accessed October 16, 2019).4. Magdalena Siwko et al., “Does isoprene protect plant membranes from thermal shock? A molecular dynamics study,” 198-208.