The Copper River flows cold and fast out of the heart of Alaska, 300 miles through rocky canyons and past calving glaciers until it branches into a broad delta of wetlands and into the Gulf of Alaska. It is a river of wild salmon and seals and drowning men, and my imagination has been swirling in those waters. Now, on a sunny July day, I set afloat in its current. My husband Sam and I will spend the next five days alone, rafting the most remote 80-mile stretch of the Copper River. We are armed with a tent, camera, maps, freeze-dried food, chest waders and a rifle for bear protection. There will be no mobile-phone reception or contact with civilisation. We will be completely on our own. The prospect both thrills and terrifies me.
"We don't want to end up against those rocks," Sam says. He gestures downstream to Salmon Point, a rocky outcropping where people catch salmon with long-handled nets. Three weeks ago a fisherman fell from the rocks not far from here and drowned, his body swept away by the river.
The raft is pushed and pulled towards the rocks by the merging currents of the Chitina and Copper rivers, and Sam rows harder, beads of sweat forming on his brow. The 14ft raft has only one rowing seat, so all I can do is sit and watch.
When we first decided to float along the river, we considered hiring guides to take us. But those we knew and trusted were already booked for the summer, and they advised us that with Sam's experience with rivers as a biologist and fisherman, we'd be fine on our own.
With Salmon Point quickly approaching, Sam wonders aloud if we've made a mistake. He strains at the oars and puts us into a ferry position, with the nose of the raft at an angle away from the shore, in an attempt to keep us from being crushed into the outcropping or drawn into the dangerous eddy. The fishermen on the rocks watch us, and time seems to slow. We are near enough that I can see their eyes. And then the current sweeps us past and spits us out the other side towards Woods Canyon. Back at home, on our kitchen counter, we'd left a hastily typed note: "In the event of both of our deaths, Samuel Service Ivey and Eowyn LeMay Ivey…"
In late afternoon we pitch our tent on the sandy bank and unroll our sleeping bags. "There's a lot of bear sign," I say, looking towards the willow bushes and cottonwood trees. "Yep." More than anyone I've known, Sam is at home in the Alaskan wilderness. He awoke in a tent once with a black bear nosing him in the shoulder. Years ago, when a sow grizzly bear with three cubs charged at us, he calmly took out his pistol and shot into the ground to frighten her away. But even he is wary here. We passed up a previous campsite because the ground was riddled with bear tracks. We start a campfire and heat water to make our dinner.
"Look," Sam says, and shows me the best-before date on the freeze-dried meal of pasta primavera. "Best used by 2018." "Yum!" I say with exaggerated enthusiasm, and we both laugh.
The next morning, a dozen people on two larger rafts float past. They call out to us, asking where we intend to camp next. "Dewey Creek", Sam answers. "Watch out for the bears," one of the women shouts. We all wave cheerfully at each other. They are the last people we will see for four days.
The float is easy now. When the river braids, Sam rows us into the larger channel, but mostly he leaves the oars at rest. The land changes, leaving behind the stunted shrubs and rolling hills of interior Alaska for the snow-capped mountains and tall evergreen trees of the coast. As we float, Sam and I talk – about jobs, family, my book, our plans for the future. When we stop talking, it is so quiet we notice a strange, slithering sound that we realise comes from the tiny grains of silt in the river gliding along the bottom of the raft.
On the third day, we spot a brown bear with two small cubs on shore. At first the animals are so far away I can barely see them. As the raft draws closer I watch the sow pause mid-stride to look back for her cubs, and my heart quakes.
How can I come to know this wild river? By following its current and sleeping with its roar in my ears? Or is it revealed through facts? The Copper River discharges 1m gallons of water a second. More than 2m wild salmon swim upstream each year. Even in summer, the temperature of the river barely rises above freezing and, with the fast current and heavy silt load, those who fall in without a life jacket are likely to drown and their bodies never be found.
Perhaps the river is defined by history. In 1908 a copper mine in the mountains sparked construction of a railroad teetering along the edge of the Copper River; the mine has been abandoned for decades, the tracks are sloughing off into the water. Follow the river back in time, to the mid-1800s, and several Alaskan Natives killed their Russian captors as they travelled up the frozen waterway. And for thousands of years before that, the indigenous Athabascans earned a hardscrabble life on its shores.
But maybe the Copper is more intimately known by its afternoon sand storms, or the icy fog that settles along the bends in the early mornings. Or the harbour seals bobbing and splashing as they chase salmon; the beaver, coyote, fox and wolves that wander down its valleys; the silver willow and fireweed thriving on its muddy banks. Or is the river simply this cold, gritty water at the tips of my fingers as I let my hand trail off the edge of the raft?
It is no easier to define a marriage. In 1993, on an Alaskan summer day, we made our wedding vows. Two daughters, two careers, a home, a life together – is this a marriage? Perhaps it is better distilled to this moment: each of us with a cup of wine, a blazing driftwood fire throwing sparks into the night sky, the Copper River rushing through the darkness, and neither of us wanting to be anywhere else in the world.
The river carries us down through the mountains and spills us into Miles Lake, cradled between two glaciers. We have been warned that the three-mile lake is sometimes blocked by ice dams even in the middle of summer, so we are relieved to find the water empty of icebergs. On the far side, we can see the bridge leading back to civilisation. Tomorrow, we'll row across the lake.
On the sandy shore, we sit outside our tent, drink the last of our bottle of wine and watch small pieces of ice float on the water. Our adventure is winding to an end. But in the dark of night we are startled awake by a splitting boom, like dynamite being detonated. We sit up in our sleeping bags. Miles Glacier is calving, great chunks of ice falling from its side and crashing into the lake. Again, and again – all through the night. We can't sleep, not just because of the noise, but because of what it might mean.
When we stick our heads out of the tent the next morning, our fears are confirmed. The passageway across the lake is filled with house-sized chunks of glacier ice. "Maybe we can make it through there," I say, pointing. Just then the huge shards of ice grind and shift, and what looked like a small berg overturns with a deep "sploosh," revealing its blue underside that now towers 20ft into the air. "We could get crushed in that," Sam says. We decide to waiting another night to see if the ice floats away, but in the meantime, the glacier continues to calve.
Just after noon, we spot a narrow open channel along the shore and around the ice jam. We get in the raft, and Sam studies the currents to see which way the ice will move when it does. As he cautiously rows us between the icebergs, I feel the cold radiating off their glistening sides. We are tired and weather-beaten when we arrive at the far side of the lake. We haven't bathed in nearly a week and we smell of wood smoke.
At the bridge, a massive brown bear lumbers down the dirt road. Just before it reaches us it stops, paces, and turns to disappear into the forest. Tomorrow, my mother will drive down that road, our two daughters grinning in the back seat. By afternoon, we'll be in a hotel room in Cordova.
But we have one last night on the Copper River. We camp near the bridge. As I lie in the dark with Sam, the brown bear is a shadow at the edge of my consciousness. Just downstream, a chunk of blue-white ice the size of a 10-storey building falls from the side of Child's Glacier into the river. The crash roars like thunder, and the ground trembles beneath me. I reach over to squeeze Sam's hand.
The Snow Child by Eowyn Ivey, one of the Waterstones 11 authors, is published on 1 February by Headline Review. To order a copy for £11.99 with free UK p&p, go to guardian.co.uk/bookshop, or call 0330 333 6846
Frontier Canada (frontier-canada.co.uk; 020 8776 8709) offers eight nights in Alaska, including five days rafting/camping on the Copper River with guide and return flights from London, from £3,267pp
