Lichen and Volcanic Glass: The Gentleness of Decay
Article 14 / 15
7 min de lecture
On the Azores, glass moves in two directions.
It rises, and it returns.
Long before anyone lit a furnace, the earth was making glass. This entry leaves the torch for the volcano: for obsidian and glassy ash, and for the lichens and the many other beings that live with them, slowly turning glass back into soil. It grows out of my research into the ecosystems that glass moves through, and a residency proposal I wrote for Faial, in the Azores, where the Capelinhos volcano erupted in 1957 and 1958.
Glass from the earth
How volcanoes make glass
Volcanic glass forms for the same reason all glass does (see What Glass Is): molten rock cools too quickly for its atoms to arrange themselves into crystals, and the disorder is frozen in place. Lava rich in silica is thick and sticky, and when it meets air or water it can solidify before crystals have time to grow.
- Obsidian is dense volcanic glass, usually black, sometimes brown, green or banded, or spotted with small white crystals in "snowflake" obsidian. Thin edges are often translucent. It fractures into edges sharper than steel, which is why people shaped it into blades for many thousands of years.
- Pumice is volcanic glass so full of gas bubbles that it can float.
- Volcanic ash is not ash in the sense of something burnt: it is mostly tiny shards of glass and rock, made when gas-rich magma shatters in an explosive eruption.
- Pele's hair and Pele's tears, named after the Hawaiian volcano deity, are threads and droplets of glass drawn out by the wind from fountaining lava.
Glass that does not last forever
Natural glass is not permanent. Over very long times it slowly takes in water and, given enough time and warmth, begins to crystallise: it devitrifies, as an overheated rod does at the torch, only over millions of years. This is why most obsidian is geologically young, and very old obsidian is rare. The slow intake of water forms a thin hydration rind on every fresh surface, and archaeologists measure its thickness to estimate the age of obsidian tools, a method called obsidian hydration dating.
Lichen: a partnership
A lichen is not one organism but a partnership. A fungus builds the body, and inside it lives a photosynthetic partner, a green alga or a cyanobacterium, that makes sugars from light. The fungus offers shelter, moisture and minerals; the partner offers food. Research in recent years has found that many lichens host further companions, such as yeasts and bacteria, so a lichen is closer to a small community than to an individual.
Lichens can live where almost nothing else can: on bare rock and fresh lava, on roofs, gravestones and old glass. They dry out and wait, and come back to life when wet. Many grow only millimetres a year, which makes them timekeepers of a kind: lichenometry estimates how long a surface has been exposed from the size of the lichens on it.
How lichens digest glass
Lichens settle on the surface of volcanic glass and begin, grain by grain, to dissolve it. They work in two ways at once:
- Physically: the fungal threads, called hyphae, grow into the micro-fractures and bubbles of the glass. As the lichen swells when wet and shrinks when dry, it prises small fragments loose.
- Chemically: the lichen releases acids, oxalic acid above all, along with compounds found only in lichens. These draw metal ions such as calcium, magnesium and iron out of the glass, and often lock them into new crystals of oxalate at the boundary between lichen and stone.
In the language of the first entry: the acids carry away the modifier ions that sit in the gaps of the glass network, and the silica network, left open, weakens and crumbles. Because volcanic glass is disordered and unstable, it weathers faster than crystalline rock of a similar composition, and studies of young lava flows have found that rock covered by lichens weathers faster than bare rock beside it.
For something to decompose, it must first be porous.
Porosity is the precondition of this alliance. Obsidian and volcanic glass, with their micro-fractures and vesicles, are open enough to be inhabited, and it is that openness that lets the lichen take hold.
A multispecies community
What the lichen begins, others continue. Ecologists call the colonisation of a new, bare surface primary succession, and lichens and mosses are often its pioneers. As the glass breaks down and lichens die and decay, the first thin soil gathers in the cracks. Moss follows, then ferns, then flowering plants, insects and birds.
The metals travel too. Obsidian and volcanic ash are dense with iron and other elements; as the lichen acids free them, they pass into the soil and into the tissues of what grows next. A metal released from a shard of glass can become part of a leaf, a wing, a flower. Colour becomes a language shared between the geological and the living, a way the volcano speaks itself through everything it becomes.
Capelinhos
Between 1957 and 1958, the Capelinhos volcano erupted off the western tip of Faial. It added new land to the island and buried houses, fields and a lighthouse under glassy ash, and the emigration that followed reshaped the community. Decades later, the recovery is carried by the beings able to reach it: lichens and mosses preparing the ground, the Azorean heather Erica azorica and the faya tree Morella faya taking root, seeds arriving in the digestion of migrating birds and on the backs of waves, terns returning each season to nest on the bare cones.
The rhythm is more-than-human.
An other velocity,
to undo the urgency
with which we usually relate to nature.
The usual vocabulary reads Capelinhos as disaster: loss, burial, departure. I am interested in what the eruption looks like from the position of the lichen, the tern, the mineral, the soil still forming, without erasing the people of Faial. Seen from there, the eruption is also an invitation, and human resilience becomes one thread in a wider symbiosis in which glass, stone, fungus, alga, plant, bird and human compose one another.
Glass that returns
Glass also comes back from the sea. At the crossroads of transatlantic routes, the Azorean shore has received centuries of human residue since the fifteenth century: wine bottles, medicine jars, tableware and tiles, thrown into the water or lost in shipwrecks. The Atlantic grinds them against volcanic sand until they become sea glass, softened and frosted, and returns them to the beaches of São Miguel and Faial. The frost is not only scratching: in seawater, glass slowly loses some of its sodium and calcium, leaving a pitted, hydrated skin.
Lichens live on human glass too. On old church windows they settle with fungi in dust and moisture, and their acids pit and cloud the surface, one of the reasons medieval glass in damp places is so carefully conserved. It is the same digestion as on obsidian, only faster: medieval potash glass is far less durable than borosilicate or modern window glass.
Offering glass to the lichens
This is where my investigation is heading. In my proposal for Faial I describe following this long metabolism as one continuous body: collecting, within local regulation, small amounts of ash, soil, volcanic glass and sea glass while walking again and again from the bare cone to the recovering slopes; carrying those minerals into my flamework in Barcelona, so that the territory itself colours the glass; and making glass structures to be offered to the lichens and slowly digested by them.
Alongside it, a lexicon: the community's words for the land and the eruption, gathered with the signs that structure the place, the seasons of the birds, the spread of the lichens, the returns of the sea. Listening across registers, as Pauline Oliveros proposed in Quantum Listening, as a continuation of How to Practice Porosity.
Decay as an intelligence, a multispecies labour of repair.
From the volcano back to words: the final entry gathers the language of glass into a glossary to keep at hand while reading and making.
