Its behaviour had been disturbing me for days now (though I was half a world away from Iceland). I'd been sunning myself on the sublime Indonesian island of Gili Trawangan, spending my days snorkelling coral reefs and nights working through the cocktail list at the hip Horizontal bar. But when I glanced to the east, slate grey storm clouds smothered the volcano's profile, though the rainy season was supposed to be over. Periodically, plumes of smoke belched from its cone.
The scale of the mountain (3,726m) is such that Rinjani lords itself over the entire northern half of the island of Lombok in every way. Ash emissions bring fertility to the island's rice fields and tobacco crops; its elevation acts like a magnet for rainclouds. Unsurprisingly, Rinjani is a revered mountain, a pilgrimage destination – and I'd delayed the challenge too long. I had to hike the peak.
Just 50km east of Bali, there's a gentle hum about Lombok that's developing into a distinct buzz. Those in the know are here already. They've had enough of the overdevelopment and gridlock that plagues southern Bali and are opening hip hotels (such as the stylish Qunci) and transforming Lombok's west coast and Gili islands into a kind of Eastern eden.
Visually, Lombok easily matches Bali's appeal. Its north-west coast is defined by a beautiful succession of sandy coves while the island's southern shore boasts legendary surf breaks and breathtaking beaches. Culturally, most islanders are Sasak, a Muslim people with mystic traditions, though there's also a significant Hindu minority (of Balinese origin). Just a generation ago in rural parts, many people were Wektu Telu (Muslims with a unique sufi-like heritage, not averse to alcohol or pork). Hindu and Wektu Telu communities still worship together at the Pura Lingsar temple just outside the Lombok capital Mataram, where Muslims give offerings to the Hindu deity Vishnu.
I am no mountaineer. But the sun was out, and the village of Sembalun Lawang, suspended in a lush highland valley between the peaks of Rinjani and Nangi, was looking its best. We were some of the first hikers of the year (Rinjani is closed during the wet season due to the threat of landslides), though lingering rains and minor eruptions meant that a summit attempt might not be possible. I shook hands with my guide and with Nyopi, our porter, who carried 30kg of gear on a bamboo pole and preferred flip-flops to boots. Nyopi explained that the best approach was palan-palan ("slowly, slowly"). I had to agree.
The path meandered past fields of garlic, rows of chilli bushes and then grasslands. A steady climb followed past mountain shelters, where the heavens opened in truly tropical style. Ahead was a near-vertical ascent of 900m up river beds and muddy gulleys sprinkled with volcanic pebbles and ash that sent me skidding into the dirt. We pushed on higher through cloud forest, home to wild boar, porcupine and towering pines, stopping to watch pied flycatchers swoop through the mist.
Soaked with sweat, legs trembling, we eventually emerged at the cloud-wrapped crater rim. Home for the night was a campsite on the edge of the caldera at 2,600m, my bed a mattress of black volcanic sand. Great clouds of smoke erupted from the highly active micro peak of Gunung Baru below, darkening the afternoon sky and coating my face with abrasive specks of ash. We dined on noodle soup before rain and exhaustion sent us to bed at 7.30pm, a howling wind inhibiting sleep and threatening to blow us off our perch into the abyss.
At 2.45am our attempt at the summit (a five-hour return hike) was called off, as the gale continued. But at daylight the weather had eased, and the skies cleared to reveal the great Rinjani caldera in all its brutal, smoking glory. Below us was the ink black crater lake of Segara Anak (Child of the Sea), where Hindu pilgrims cast pearls and gold into its sacred waters and Wektu Telu offer life savings instead of spending their cash on the pilgrimage to Mecca. As the sun climbed higher, the sky changed to an electric blue. In the distance, the perfect cone of Agung in Bali pierced the horizon. I sat and contemplated the forces of nature that had created this astonishing landscape, for Rinjani is only a fraction of its former self – thousands of years ago a cataclysmic eruption blew the entire lid off the Rinjani supervolcano, reduced the volcano's height from about 5,000m to 3,726m and created the 9km-wide caldera and crater lake.
Two days later, my body was still in bits. I had tendonitis in my city knees and my thighs had all the flexibility of concrete (despite my palan-palan descent). Fortunately, the Lombok Oberoi proved to be a fine place to recuperate. The hotel is built around a triple-level pool which extends to a white-sand beach, with a coral reef offshore. Accommodation, built from natural materials (honey-coloured stone and thatched roofs) is dotted around a coconut grove. I loved sharing tales of pain with the staff, many of whom had made the Rinjani climb.
One morning I hobbled around the sandy bay to Tugu, an astonishing fantasy of a hotel, and home to Lombok's finest spa. Here, under the gaze of centuries-old Javanese statues, my Sasak masseur, Riadi, teased and plied my shell-shocked limbs back into some kind of humanoid form. While I lay mesmerised by the sound of the ocean, I marvelled at the complexity of Indonesian culture.
Southern Lombok is drier, less developed and has been touted as the island's next big thing since anyone can remember. Plans for a mega-resort (backed by the Dubai-based Emaar group) appear to be moribund following the Emirate's financial crisis, but with a new airport soon to open, changes are coming, and the scruffy one-horse town of Kuta now has three estate agencies.
I found a virtually pristine coastline, visited by Aussie surfers and the odd backpacker. I signed up for a day of surf instruction at Gerupuk bay, and felt the raw power of southern Lombok's waves, which propelled me 200m from break to beach before spitting me out in a blur of foam, salt and spray. The next day I took a moped west of Kuta, pausing at Ashtari café for breakfast to take in its coast of soaring headlands and bays. A little further west, Mawun beach left me speechless, a half-moon cove of perfect proportions, powder white sand and azure water, framed by emerald green hills. My plan to return to northern Lombok that afternoon was immediately postponed: the beauty was too overpowering, the place too special to experience in an hour or two.
Back in Kuta I asked Made, my guest house owner, about Mawun. He said that a Chinese hotel group had plans to build a big resort there, but they were sitting on the land for now. "No water pipe, no electricity," he explained. So for now it seems the coast is clear. "Yes," smiled Made. "palan palan."
Travel essentials: Lombok
* There are no direct flights between the UK and Lombok. The writer flew on KLM (08705 074074; klm.com) via Amsterdam to Jakarta, Java.
Singapore Airlines (0844 800 2380; singaporeair.co.uk) and its Silk Air subsidiary connect Heathrow and Manchester to Lombok's Mataram airport via Singapore. You can also reach Bali with airlines such as Qatar Airways (0870 770 4215; qatarairways.com/uk) from Heathrow and Manchester via Doha.
* Numerous fast boats connect Bali with Lombok and the Gili Islands including Blue Water Express (00 62 361 895 1082; bwsbali.com) from 1,100,000Rp (£79) return.
* Qunci Villas, Senggigi (00 62 370 693 800; quncivillas.com). Doubles from US$85 (£57).
* The Oberoi, Medana (00 62 370 6138 444; oberoihotels.com). Doubles from US$417 (£278).
* Tugu Hotel, Sire Beach (00 62 370 612 0111; tuguhotels.com/Lombok). Doubles from US$272 (£182), room only.
Eating & drinking there
* Horizontal Lounge, Gili Trawangan (00 62 370 639248; thegiliislands.com).
Red tape & more information
* British passport-holders require a visa to visit Indonesia. These are obtainable on arrival for $25/£16.70 (020 7499 7661; indonesianembassy.org.uk).