The airplane is full of honeymooners. We are flying south from Seoul, escaping winter’s icy grip, and leaving behind the daily stresses of a city of 10 million people. The atmosphere in the cabin is joyful, infused with the optimism of dozens of recent weddings.

Many of the young couples are holding hands, smiling, carefree. I suspect that they are unaware of the geological and social peculiarities of our destination. Just as well. From what I know of the place, I can’t help wondering if Jeju Island is the most auspicious location to begin a marriage.

Situated in the Yellow Sea, 50 miles off the southernmost tip of the Korean peninsula, Jeju is by far the largest of the 3,000 islands speckled around the mainland. It is roughly oval shaped, about half the size of Rhode Island, and has the distinction of being South Korea’s only autonomous province.

At first glimpse, Jeju-do as it is usually known (do means both island and province) lives up to the promises of the glossy tour brochures. Its climate is sub-tropical. There are palm trees and beaches. The interior is lush and green. The resorts are luxurious. Romance is in the air, as obvious and persistent as the pall of cloud that invariably veils the summit of Mount Halla in the very center of the island.

Only on rare days when it is fully revealed does the brooding mountain provide evidence that Jeju-do is not entirely benign. At 6,398 feet, Hallasan is South Korea’s tallest mountain. When I ascend one of the four trails leading to the summit, the evidence of its violent origin is plain to see. The path is strewn with crunchy basalt rock, the legacy of volcanic eruptions.

Mount Halla has been dormant for a thousand years, but it casts an ominous, primeval shadow over the island that it created. Sometime in the next millennium it is likely to burst into life again, and the honeymoon resorts — if they are still here — will be in the line of fire.

Jeju-do lives up to its billing as the Hawaii of the Orient, with its volcanic heritage, its rugged beauty, its rich vegetation and its thriving tourist industry. Yet there are notable differences, especially in winter.

Scaling the southern flank of Mount Halla, I pass a Buddhist temple, which stands in meditative silence beside the path. Birds twitter in the woodland of the lower slopes. A frosty stream gurgles among the undergrowth. I am alone. The reason nobody else is on the path today eventually becomes clear. After an hour of walking, I reach the snow line. The upper half of the mountain is entirely blanketed. The going is suddenly treacherous, and I have no option but to turn back.

On the descent, the temperature rises and the air becomes more humid. My surroundings are draped in eerie mist. Ahead of me I make out a spectral figure standing to the right of the path. It appears to have stepped aside to let me pass, though as I get closer I realize that it is, in fact, rooted to the spot. I am face to face with a dolhareubang — the symbol of Jeju-do. It is about eight feet tall, carved from lava, and is reminiscent of the statues of Easter Island. Like its famous counterparts, the origins of the dolhareubang are lost in time. All we know for sure is that for centuries the landscape of Jeju-do has been dotted with these odd figures, with their bulging eyes, hunched shoulders and rudely suggestive hats.

Dolhareubang translates as “stone grandfather,” though the moniker is relatively recent. Who made them, and why, remains open to speculation, though the most likely theory is that the statues are linked to ancient, mushroom-worshipping shamans who crossed to Jeju-do from the mainland. Whatever they used to be, today these distinctive statues are the must-have Jeju-do souvenir. When I return to my accommodation at the Hyatt Regency — a strikingly designed hotel that sits like a landed spaceship atop a bluff overlooking a beautiful beach — I discover that the lobby shop sells a complete range of stone grandfathers, from pocket-size to life-size.

In recent years, the stone grandfathers have been touted as fertility symbols, though honeymooners pinning their hopes on any mystic powers possessed by these lumps of basalt will probably be disappointed. There appears to be no historical basis for such a claim. However, another aspect of island culture could have a profound impact on the aspirations of the newlyweds, for, uniquely within South Korea, the villages of Jeju-do are matrilineal. Family ancestry is traced through the female line, and women are the heads of the household.

One morning, I walk along the cliffs to the west of the hotel, and witness female empowerment in action. Far below, a group of ruddy-faced women in wet suits are waist deep in the surf. These are the haenyo, or sea women; female divers who, weighted with stones and holding their breath, dive to depths of up to 60 feet to gather lucrative catches of abalone and conch. The haenyo are the principal breadwinners in their families, putting in a hard (and often dangerous) day’s work while their husbands raise the children and take care of the chores.

This role reversal may not last much longer. Fifty years ago, there were 30,000 haenyo in Jeju-do. Now there are just 5,600, most of whom are past the age of 50; only two are under 30. With numbers set to dwindle rapidly as the older divers retire, the proud haenyo culture looks set to disappear within 20 years. For now, though, they are a popular tourist attraction. I share the cliff-top with dozens of honeymooners. The couples appear uncomfortable to be confronted with this alternative blueprint for married life.

I leave, flying back to Seoul. In common with most visitors, I am carrying part of the island with me. Literally. In my suitcase, there are two dolhareubangs. It is not just the haenyo under threat. In a couple of decades, will there be anything left of Jeju-do itself? Or will the island have been entirely removed, piece by piece?