Know Your Neighbours: A river Runs Through It

June-July 2001

This is an article from WaveLength Magazine, available in print in North America and globally on the web.
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by Bryan Nichols

Familiar ocean vistas of Gulf Island's sandstone or Coast Range granitics get more complicated when we sea kayakers venture inland into rivers and lakes. While I consider paddling fresh water to be slumming biologically, it is a great opportunity to learn about geology. A river literally runs through the past, providing spectacular scenery while slicing through millions of years of geological drama-if you know what to look for.

Geology is one of those subjects I probably shouldn't have avoided so effectively back in my school years. It's still a tough sell in a textbook, but if you have a curious nature and travel outdoors much, you can't help wondering how those lovely landscapes formed. Field learning, especially in the Parks systems, is the best way to brush up on your geology. This will help get you started.

ROCK ON

Rock forms in three basic ways and Northwest paddlers drift past excellent examples of each. If it "congeals" from a liquid (magma) then it's igneous-those salt and peppery granitic rocks throughout the Northwest formed that way deep underground. Lava flows in the interior cooled at or near the surface.

Rock that is laid down in rivers, lakes and oceans as sediments and then "gently" squeezed is called (helpfully) sedimentary. Sandstones and conglomerates are fine examples and may contain fossils of critters that were buried and preserved in the process.

After igneous or sedimentary rocks get squeezed and baked by intense pressure and/or heat, they are called metamorphic because their nature changes significantly. A good example is marble, which is morphed limestone.

TIME KEEPS SLIPPIN'
Most of us relate to time on the scale of number of shopping days until Christmas. We therefore find it difficult to plan for "future generations" that may only be a decade or two off. Grasping the concept of geological time is next to impossible. The earth is over four billion years old-our lifespans, our civilizations, are barely blips. Geological processes (usually) move so slowly in comparison to our lives that we are hard pressed to even recognize them.

TECTONICS AND TERRANES

It wasn't so long ago that we figured out the earth's surface was mobile and big plates of it have been shifting around for billions of years. After considerable initial reluctance, plate tectonics became something of an epiphany, a giant lightbulb going off over the collective heads of geologists-suddenly a whole lot of things made sense.

B.C. is a complex mess of plate tectonics because a series of chunks called terranes have drifted into it over the last few hundred million years, piling up mountain ranges, uplifting and twisting layers of old sediments, triggering massive bouts of volcanism and generally making things hard to figure out. Erosion has since buried many areas with newer sediments, but with a good geological map you can find areas of rock at the surface that came from far off parts of the world, carried here on slow but unbelievably powerful currents of magma deep below us.

The terranes have mostly stopped slamming into us for now but plates still continue to slip and shift, most notably near Vancouver Island and Haida Gwai. Mountains continue to rise as well, for two reasons. One is rebound, as the earth slowly springs back after being depressed by the immense weight of the ice age glaciers. The other is heat expansion-the coast range in particular is still swelling upwards thanks to the heat generated below it as one plate slides under another.

Of course geology, like life, has its share of downs as well as ups. Bringing all this rock back down to earth are the processes of erosion. Wind, water and good old gravity all conspire to move immense amounts of rock from high points to much lower ones. The Fraser River alone carries about twenty million tons of rock into the ocean every year (much of it as silt). Water can eat through rock at surprisingly rapid rates, especially when freezing and flooding are involved.

CHILL OUT

Finally, most of the landscape in the Northwest was drastically altered by the last "ice age" about 12,000 years ago (very recent, geologically speaking). For the past couple of million years, vast ice fields have made numerous advances and retreats, spaced about 90,000 years apart. Many of the items on this issue's checklist are direct evidence of the sheets of ice that last covered the Northwest. We'll start with familiar ocean sandstones and work our way upstream, finishing with cirques at the top of the mountains, the headwaters of our rivers and birthplace of the next group of glaciers.

Biologist BN would like to thank America's dazzling and informative National Parks System for providing him with the world's best course in geology over the years. The best way to learn geology? Road trip!

Further Reading-Geology of BC: A Journey Through Time by Sydney & Richard Cannings. 1999 Greystone. 1-55054-704-6 $23 Cdn. This small book is a great introduction to the spectacular geology of BC. Packed with beautiful photographs.

Checklist # 20 - GEOFORMS

BEEHIVES? Salt spray, wind and waves carve relatively soft coastal sandstones into some remarkable patterns. Malaspina Galleries off Gabriola is one of the better examples but throngs of Gulf Islands paddlers are always asking about the pockets and mosaics we paddle past. When guiding I often explain that "rock bees make them" just to see who believes me.

FOSSILS The Burgess Shale near Field, BC is one of the world's best known fossil sites thanks to its abundance of quality fossils from a mind boggling 530 million years ago. But there are plenty of other fossil sites in the Northwest, from dinosaur trackways to vast coal forests, from Courtenay's scary marine reptiles to ancient whales off Victoria. Hunting for evidence of life long extinct etched into stone is an addictive pastime.

SCRAPE and PLUCK Though it sounds like a poultry related chore, this is what glaciers can do to outcroppings of bedrock in their way. It results in a distinctive smooth side where the ice scraped its way up, and a much steeper cliff edge where it plucked off big chunks along faults. Circumnavigate many of the Gulf Islands and you'll see this up close.

GLACIAL POLISH Where tough bedrock resisted the power of the glaciers you might spot polished areas, rock worn smooth by the passing ice. It often has small scrapes that show the direction of travel. You'll find great examples anywhere from high up on the sides of valleys down to sea level and below.

ERRATICS Another great bit of ice age evidence obvious from a kayak are glacial erratics, huge chunks of rock that sit conspicuously in places they don't seem to belong. Paddlers in the San Juans often spot big granitic boulders sitting on the sandstone, rocks from up in the Canadian Coast Range that emigrated and then were left stranded by retreating ice.

LIMESTONE CAVES Areas with a lot of sedimentary limestone (like Gold River & Nimpkish Lake) often erode into a distinctive terrain called karst. Caves and sinkholes are common and entire rivers can literally disappear underground. If you've got the speleological bug, contact the caving association nearest you for advice and locales.

PLUTONS Forget the dog and the planet, plutons are vast blobs of magma that cooled deep underground. If a pluton gets uplifted without developing many faults or cracks it can erode out of the ground as a huge, solid mass. The West Coast has many, from Yosemite's famous domes to the Squamish Chief. These massive granitic cliffs make for great climbing and great scenery.

VOLCANOS As the Pacific plate slides under the North American, it triggers quakes and spawns volcanoes. Shasta, Lassen, Rainier, Baker, Hood - these immense mountains of igneous rock dominate the local scenery and remind us that on (thankfully) rare occasions, geological time can be catastrophically fast.

LAVA FLOWS Venture upriver through the Coast Range and you'll run into numerous areas where huge flows of molten rock have filled valleys. Along rivers near Pemberton, lakes in the Okanagan and in parks like Lava Beds and Wells Gray, liquid stone was a reality. Pondering huge rivers of rock is especially soul-stirring for us kayakers.

COLUMINAR BASALT When lava cools quickly, it often cracks vertically to form hexagonal columns. The color of the basalt may vary but you'll spot these columns eroding out of cliffs in volcanic areas throughout the Northwest-check out the one on the highway as you approach Whistler.

HANGING VALLEYS When big glaciers scrape their way down major drainages they leave behind a "U" shaped valley instead of the narrow "V" shaped valleys that flowing water cuts into rock. Because of the scouring power of the ice, smaller feeder valleys can be left hanging way up on the sides, often with spectacular waterfalls joining the main river.

CIRQUES At the end of our inland journeying are the crests of the mountains. When glaciers form they pluck away at rounded mountain tops-now they are gone (or much reduced) we are left with bowls surrounded by very steep, thin crests. These distinctive cirques will hatch the next crop of glaciers, if global warming doesn't melt us all first.