Our van rumbles down a road that leads to the very heart of the tectonic rift system while our guide, David Sigthorsson, tells us about the myths of Norsemen who settled his home country.

Embraced by volcanoes on either margin, this foreign landscape intensifies all of our senses. Long stretches of evergreen grasslands, yellow and orange wetlands, and little streams of bright-blue water pass by my window as if on their way, as we are, to Thingvallavatn Lake, two hours east of Iceland’s capital, Reykjavik. Rain and glacial water traverse unconventional routes on their way into this basin. Most of the glacial water from Iceland’s second-biggest glacier, Lángjökull, filters through the porous basalts for hundreds of years before welling up in the many fissures found around the lake. That is why it is so clear and clean, a diver can drink from it. But there is a price to visiting this wondrous place: water temperatures of 36 degrees.

A convenient staircase allows me to descend into Silfra, or “Silver Lady,” one of many ruptures caused by tectonic activity. The cleft is quite narrow, its deepest point around 195 feet. A steep wall of magmatic rock near the entrance guides me into a labyrinth of cavities, arches, troughs and saddles filled with the planet’s purest fresh water. Above my head, a shimmering effect turns the surface into a silvery mirror. Only at the very end of the dive am I reminded of the limiting temperatures.

A short break in the bright but faint summer sun gives us enough warmth to continue our dive in a shallow lagoon. At the bottom, just above bright-white sediment, tiny gas bells cause wisps of light-green algae to flutter softly in their stream. Soon we re-enter the main fissure, and a cathedral of massive basaltic boulders steals my breath. Here Earth is split in two by energy coming from the deep mantle below. We are diving between continents, on the Mid-Atlantic Ridge system.

Geologically speaking, Iceland is very young, roughly 20 million years old. Much of its landscape has not yet been leveled; Europe’s most powerful waterfalls tumble from great heights as they carve their way into lava fields. It is one of the most active places in Europe, home to more than 30,000 live volcanoes.

The island consists of volcanic rock generated at the Mid-Atlantic Ridge, a mountain that stretches north to south along the entire Atlantic Ocean. Here two tectonic plates are being pushed apart, leaving a gap in the middle, where hot magma rises and crystallizes on the ocean floor; much of the ridge lies below the surface of the water. In some areas, the ridge rises above sea level, creating this island country. Iceland is also situated above a hot spot, a region of high volcanic activity due to the rise of a hot mantle plume, similar to the Hawaiian Islands. Mantle plumes come from much deeper than the average mid-oceanic ridge — nearly 2,000 miles below the Earth’s crust.

Led by David Sigurthorsson from Dive.is, Iceland’s biggest dive operator, we start a 10-day journey around the island. Diving in Iceland is slowly becoming more popular; fortunately for us, few of the locations on our schedule are commercialized. Not many diving facilities exist — tanks are filled at fire departments.

When sudden volcanic activity on our second day forces us to abandon the coastal road to the east, Sigurthorsson questions whether inland rivers and unpaved roads will be passable. Cautiously, he decides to wait for outfitted Jeeps to cross the rivers before guiding our heavily loaded van through the water. Inland, the volcanic landscapes are as varied as the pages of a geological textbook. Black, barren moonscapes are covered with pumice and volcanic bombs, providing NASA an ideal place to train astronauts for moon landings in the ’60s. We round a corner, and all of a sudden, rivers are carving into glowing hills and valleys, and nothing remains to remind one of Iceland’s destructive nature.

When evening sets, we finally arrive at the southeast coast of Iceland. Here its biggest glacier, the Vatnajökull, flows majestically down the mountain and calves icebergs into a shallow lagoon. The icebergs will have to melt before crossing an even-shallower pass into the ocean. Some of them are colored black by ashes from last year’s eruptions, which indicates that the iceberg has not turned since. Seals march up and down next to the ice, and give us a curious look before disappearing in the dark water.

On a thick, mussel-covered rope, I descend into Seyois fjord, just at the foot of a small authentic fishing village in the east of Iceland. The fjord is a spectacular U-shaped valley carved by a glacier that has now receded. On the ridge of the valley lies a thick cover of snow, even in summer. Although the ocean water is said to be a few degrees warmer than the fresh water in Silfra, the cold soon seeps in, and it does not take long before darkness envelops us. El Grillo, a 7,000-ton, 278-foot-long oil tanker, slowly contours in the beam of my light.

It must have been a cold day on Feb. 10, 1944, when British soldiers stood against the railing watching German forces approach from the sky. El Grillo was built by the British in 1922 and positioned in this natural harbor during the Second World War to supply the Allied forces with fuel. The ship took a serious hit but did not sink right away. Out of fear that the Germans would return, its crew sank El Grillo that same day.

Today we conduct two dives. The deepest part of the ship is at 146 feet, and it reaches up to about 91 feet. We descend upon a metal frame covered with little sponged, echinoderms and crustaceans. Despite the limited bottom times, this dive into Iceland’s history provides another amazing experience.

From the WWII wrecks in east Iceland, we travel to Oxarf fjord, a little more than 60 miles from the Arctic Circle. In the deltaic landscape, a small crack named Nesgja connects a brackish lagoon to nearby open ocean. Unspoiled, the vulnerable environment includes thick, plasticlike microbial mats covering the rocks like a translucent veil. A bluish-green hue distorts any sense of depth, and there seems no end to it. Fifteen minutes later, we are forced upon a shallow, razor-sharp saddle of basalt that forms our way to the lagoon. Inside, the undisturbed floating algae thrives, forming a landscape of hanging curtains.

That afternoon we stop at a somewhat hidden spring in the middle of nowhere. With a grin on his face, Sigurthorsson puts our patience to the test. With only drysuit, mask, snorkel and fins, we enter water not deeper than 6 1/2 feet. At the bottom of the spring, an extraordinary phenomenon takes shape: Geothermal energy wells up and creates bubbling mud lakes and troughs where colored minerals and shells are juggled in the water column.

Our Zodiac travels full speed over the dark water of the Eyja fjord, close to Akureyri, the capital of the north. Adjoining volcanic mountains pierce the gray clouds that lie low above the water line. In the middle of the fjord, a line descends to Strýtan, a hydrothermal vent that rises from more than 200 feet up to nearly 50 feet below the surface. We are here to dive on the world’s shallowest known hydrothermal vent, called a “smoker,” a phenomenon normally restricted to the abyssal plane, many thousands of feet deep.

Our guide, Erlendur Bogason, discovered this massive white formation in 1997. When hydrothermal vents were first encountered in 1977, the scientific community was amazed to find entire ecosystems totally isolated and, more important, not dependent on sunlight. Microbes and other unicellular organisms that live in this total darkness use chemicals from the hydrothermal vents as a means of energy instead of sunlight, a phenomenon that has been studied for clues to the origin of life.

Strýtan is a white smoker, due to the white color of the clay mineral smectite carried in hydrothermal vent fluids. These fluids circulate through the oceanic crust under high temperatures and pressures, which causes them to saturate with lots of crustal elements and minerals. Upon mixing with cold ocean water, these minerals coagulate and form the chimney. The hot water — 176 degrees F — that seeps from the top of the vent causes a visible thermocline; if you’re careful, you can warm your hands by removing your gloves.

The chimneys are not the only things that make this one of the most spectacular dive sites on the planet. Big schools of pollock and cod circle the site, massive wolf eels emerge from their caves, and every rock is covered with anemones and sponges. This is how our seas should look — like a garden of life.

During our last dive, Bogason opens a thermos and fills it with the hot water. Back on the boat, he adds a chocolate mix just as a humpback decides to honor us with a visit, surfacing an arm’s length away. This is diving in Iceland.

Need To Know

• When to Go: Silfra is good year-round. Other sites, April to October.
• Dive Conditions: Silfra always offers perfect visibility; ocean diving is hard to predict and highly variable. Viz ranges from 6 to 80 feet.
• Operators: Dive.is (www.dive.is), in Reykjavik, does diving and snorkeling day tours to Silfra and other sites, as well as packages and multiple-day land and sea tours all over Iceland.
• Price Tag: Dive.is' 10-day tours start at about $3,650. Silfra Snorkel costs about $120; other multiple-day tours start at about $720 for a three-day tour.