"Now let's look for trolls. You can see hundreds here. According to the legends, the sun came up unexpectedly, caught the trolls partying and promptly turned them into rocks."
Judging by the lighter note, he must have thought we needed a break from his tutorial on continental drift. He needn't have worried. A six-hour geology lecture would have become boring anywhere else, but in Iceland it proved endlessly fascinating and barely scraped the surface of this bizarre, barren land of ice, fire and water - oh yes, and lava.
All around us the tortured shapes of the grotesque statues of Dimmuborgir stood in the freezing air, waiting for the next squall from the west. We were in the Lake Myvatn region, the best place to see the incredible panoply of geological phenomena that the country literally throws up.
But as any good guide knows, you whet the tourists' appetite and then leave the most dramatic bits until last. So Jonas took us to the remote farm where he grew up. Here, in fields of brown grass, we saw the hippies of the horse world - long-haired Icelandic ponies whose chestnut manes flopped in front of big soulful eyes.
"Now I will tell you a secret," said Jonas. "My mother is a criminal." He pointed to an old bath standing incongruously on the muddy shore of the lake. It had a feed-in pipe running into it from the bank. In the summer his mother filled it up with geothermal water from the central heating system and sat for hours reading in her lakeside bath. "The authorities say the water must go straight into the lake." Is this what being a criminal in Iceland means?
Lake Myvatn - apparently some 2,000 tonnes of flies live there in the summer - is a kind of spaghetti junction for the world's ducks. In the summer, along the river Laxa and around the scores of islands of this gigantic volcanic pond, live 28 different species. Among them are the rare Barrow's golden-eye and the harlequin, which, with its delicate painted tracery, looks as if it has swum straight out of a souvenir shop.
Over the years, the locals of Grimsstadhir established such a strong link with the ducks that they built special holes in their lava houses for the birds to nest in. Not so much out of fraternity with their feathered friends, however, as out of laziness: it meant they could nick the eggs without leaving the comfort of their homes.
In the 1960s, Neil Armstrong got a feel for the moon by donning his space suit and clambering over the hundreds of dusty brown pseudo-craters that cling to the shoreline at Skutustadhir. These eerie pockmarks, caused by steam explosions, still had patches of snow on them when we were there. And so did the mountains of Sellandafjall and Blafjall which provide the lake's spooky backdrop, their black and white slopes looking like giant somnolent pandas.
Yet sleepy they are not. Underneath, the Earth is for ever churning away, throwing out acrid sulphur, geothermal springs, geysers, and causing the odd earthquake and volcanic eruption. Like no other place I've been to, Iceland challenges one's preconceptions about the passive nature of the Earth. For most of us in suburban Britain, Nature is all about quiet green countryside where rivers occasionally flood and coasts where
the sea follows tide timetables. Such a regulated universe does nothing to prepare you for Iceland.
At Hverarond, as sulphur belches out its yellow, nostril-pinching stench and pits of boiling steely blue mud heave and bubble like Hell itself, only a thin rope separates you from death by scalding. A little distance away, the Earth's core comes hissing out of a cairn of rocks - Nature's way of letting off steam. I had the feeling that the whole ground might blow up at any moment.
My fears were only partly eased when Jonas showed us two stanchions sticking up out of the rocks. "The distance between the two metal rods is set at 5cm," he said. "When they get closer we know that volcanic activity is on the way." We were far from the nearest road. A mile off, a geothermal spring flung its column of white steam into the knife-clean air, the low sun threw its evening light beneath a band of pink cloud and the shivering wind reminded us that a huge glacier lay white and grand not far to the south. If these rods were to move, who would be there to witness it?
At Godafoss's gushing, gurgling waterfall we met Joan, an American in her 60s who was cycling alone around Iceland's coastline. She had done two weeks and had another week - and 350km - to go. She had a bottle of water strapped to her back and a blue pipe running into her mouth from which she sipped: it saved her from having to dismount when she wanted a drink. But did the water authorities allow it, I wondered. I couldn't be sure of anything in Iceland anymore. My world too had turned upside down.
Perhaps a round of golf would dispel the disorientation. Akureyri has the northernmost 18-hole course in the world and I wanted to play it. It is where the Arctic Open is held every June, a non-stop 36-hour contest, made possible by continuous daylight. Even in May, Bjarni and I were able to get in nine holes by starting at 10.15pm and finishing just before midnight. A vast northern silence was caving in on us as we reached the clubhouse.
I met the others in the bar of the Fosshotel just as the weekend was beginning. Icelanders' Friday night doesn't really start until Saturday morning. All week they work hard, then they let rip, giving Reykjavik, the once little-known capital until the days of Bjork, the unlikely accolade of Party Capital of Europe. Seismic shifts, then, were not confined to the landscape.
Man can't live by geology alone and even in Iceland you have to eat and drink. And there lies the rub. Surely the rest of Europe would flock to this enchanting little land if it wasn't so hellishly expensive? A main fish course in a decent restaurant typically costs pounds 25, and half a pint of bitter pounds 5. A bottle of wine can be pounds 30. It kind of cramps your style every time you enter a retail outlet, a shadow at the door far more oppressive than any thrown by a glowering volcano.
Our last journey was to the Blue Lagoon, a commercial version of Jonas's mum's bath. But here, supposedly medicinal blue mud was part of the peculiar concoction produced by the adjacent power station. Children on a school trip splashed in the turquoise water with their swimming costumes on their heads, while we wallowed in the warmth, pretending it was doing us good.
New state-of-the-art spa facilities at the Blue Lagoon were supposed to be open but construction was behind schedule. (They finally opened on Friday.) We were told it would be ready in three weeks. Three weeks? Surely not. Then we twigged: 24-hour daylight enabled them to work round the clock, and three weeks really meant nine weeks. Once again, the strangeness of this unsettling northern land had ruffled our ordered minds.
Robert Nurden travelled as a guest of Regent Holidays (tel: 01983 864225) and Icelandair (tel: 0171-874 1000). Flights from London to Reykjavik take three hours; from Glasgow, two hours 10 minutes. If you stay at least three nights, including a Saturday night, the fare from London is pounds 292 including tax. Note that visiting Iceland is much cheaper if you do it as a stop-over on the way to the USA.
DEALS AND PACKAGES
Regent Holidays offers 13 holidays to Iceland, including the 15-night Iceland Symphony (from pounds 1,925 per person, based on two sharing, as are all the prices), seven-night Mountain Biking (from pounds 928), and 14-night High Country Sleeping Bag Safaris (from pounds 1,204). It also has a Freedom of Choice option for those who want a tailor-made holiday. Car hire costs from pounds 64 per day.
Iceland Explorer (tel: 00 354 565 0080) is based near Reykjavik and organises exploration holidays and trips with an educational content, including Icelandic sagas, folklore and fairytales.
WHEN TO GO
Iceland is all about the outdoors, which really means the summer months of June, July and August. Take waterproofs - it rains a lot. Horse-riding, cycling, kayaking, snowmobiling, cave-exploring, white-water rafting, deep-sea fishing, whale-watching, flora and fauna trips - and good old walking - are all on offer. Visiting Thingvellir, the site of Europe's oldest parliament, is a must.
Contact the Iceland Tourist Board, 3rd floor, 172 Tottenham Court Road, London W1P 0LY (tel: 0181-286 8008).