Gyali

Gyali is a small volcanic island in the Dodecanese, wedged between the south coast of Kos and Nisyros, with two halves that tell completely different geological stories. The northeastern side is built from dark obsidian lava domes, while the southwestern half lies buried under pale pumice, and a narrow isthmus of reef sediment joins the two. The whole island covers about 4.5 square kilometres and reaches only 180 metres, roughly 6 kilometres long, 4 kilometres across at its widest and barely 500 metres at the waist, so you can take it in at a glance from the water.

A Volcano Inside a Bigger Volcano

Gyali sits within the inferred outline of the huge submarine caldera left by the Kos Plateau Tuff eruption, which took place around 160,000 years ago and blanketed much of western Kos in ignimbrite. The island itself is made up of rhyolitic obsidian domes at its northeastern end and pumice-fall deposits at the southwestern end. No eruption has been recorded in historical times, but the most recent pumice falls lie directly on soils containing Neolithic pottery and worked obsidian, which places them uncomfortably close to the period of human occupation.

The name is literal. Gyali means glass in Greek, a reference to the obsidian, and in antiquity the island was known as Istros. Today it belongs to the municipality of Nisyros, in the Kos regional unit of the South Aegean, together with the uninhabited islets of Pacheia, Pergoussa and Strongyli, all of them products of the same Nisyros volcanic complex. Seen from above, Gyali is a crescent pinched at the middle, which is why it is sometimes described as figure-of-eight shaped.

Obsidian, Neolithic Settlers and Early Metalworking

Along with Melos, Gyali was one of only two obsidian sources in the Aegean, and its stone travelled. Gyali obsidian turns up at prehistoric sites across the eastern Aegean, and the island is counted among the handful of major obsidian sources of the central and eastern Mediterranean, alongside Melos, Antiparos, Lipari, Pantelleria and Sardinia.

Surface surveys have identified prehistoric, Hellenistic and Roman sites on the island, with the obsidian quarries occupying the northeast and a Late Neolithic settlement and cemetery in the southwest. Occupation seems to have begun in the early 4th millennium BC as seasonal use of the coastal site of Laimos, shifting to the northwest of the island later in the same millennium. Two crucibles with copper still adhering to them and a lead rivet show that early metalworking was practised here in the mid-4th millennium BC. The island was then abandoned at the end of the 4th millennium and stood empty for a very long time, only being resettled after the Greek Revolution of 1821.

The Pumice Quarry

Modern Gyali is a working industrial site. LAVA Mining & Quarrying, part of the HERACLES group, has been extracting the island's pumice since 1952. The deposit is estimated at around 100 million tons, the largest in Greece, and annual output averages roughly one million tons, most of it exported. Those strip workings are what leave the southwestern shore bare and blindingly white. Alongside pumice the island yields natural pozzolana, and Gyali pumice has been studied specifically for its value as a pozzolanic additive in cement.

The population is essentially the quarry's. Just 7 people were recorded on Gyali at the 2021 census, down from 21 in 2011, and the small settlement of Chora on the isthmus amounts to housing and a port for quarry workers, served by a daily commute boat from Mandraki on Nisyros. There are no public harbour facilities, no shop and no provisioning, and landing generally requires permission from the mining company.

Seeing Gyali from the Water

All of which makes Gyali an odd but genuinely memorable thing to sail past or anchor off. On one side white pumice hills rise straight out of the sea; on the other, dark volcanic rock and low Mediterranean scrub. In the flat central strip between the two lobes there is a sandy beach, and the water offshore is startlingly clear against the pale seabed. Nisyros lies about two nautical miles away, close enough that the two are usually seen on the same day.

Because it looks like nowhere else in the Dodecanese, Gyali has become a popular stop for gulet charter guests exploring Greece, where boats anchor off its quiet coves to swim before continuing on toward Nisyros or Kos.