The Columbia Coast shares climate, topography, geology and cultural traditions across its namesake river. The river is a political boundary, not a biological barrier.

The Columbia Coast region is bordered on the west by the Pacific Ocean, on the north by the Chehalis River, on the east by a line running north and south from the east end of Wahkiakum County, and on the south by the Nehalem River. This area includes the northwest Coast Range in Oregon, the Willapa Hills in Washington, and several estuaries - Grays Harbor, Willapa Bay, Columbia River Estuary, Necanicum River and Nehalem Bay.

 

Climate

With so much water in, on and around the region, climate is dominated by the Pacific Ocean. Winters are moderate and wet; summers are cool and damp to dry. There is a distinct fog belt along the coast, with the line running about half way across the region in a line from north to south. Inland of this line, which falls about 20 miles from the ocean, summers can be quite warm and dry. Along the coast in the fog belt, summers are distinctly cool and damp.

Annual rainfall averages 85 inches along the coast in lowland areas, with a range of 50 to 120 inches. Rainfall rises sharply with elevation to more than 150 inches per year above 2,000 feet. The highest peaks average more than 200 inches. There are a few rain shadow areas where typical rainfall is less than 80 inches per year. Most of the rain falls from October to May.

Significant accumulations of snow are unusual at all elevations. Above 2,000 feet, four to six feet of snow may persist for some weeks during some winters, but rarely lingers for the entire season. Short periods of snow and freezing temperatures may occur down to sealevel once or twice each decade. Prolonged periods of freezing weather occur 2-3 times per 100 years, though of course written records documenting local weather conditions are barely 150 years old.

Summers tend to be rather dry in contrast to winters. Fog aside, it is not unusual to go 30 to 60 days without significant precipitation. About once a decade, dry spells may last up to 90 days. Local plants are adapted to this climate: they typically grow, flower and set seed early, and ride out late summer drought.

Several Words for Rain
Abundant precipitation has prompted a local accumulation of terms to describe kinds of rainfall, including fog, mist, drizzle, plain rain, real rain, pineapple express, silver thaw, and howler. Most winter rain actually falls to land horizontally, driven by fire-hose force winds.

Summers bring fair weather with northwesterly winds. These winds drive the upwelling of cold water onshore, resulting in coastal fog. Summer fog contributes critical moisture to epiphytes, helping them survive the dry season, and to coniferous trees. During periods of heavy fog, water can be seen running down tree trunks, testimony to their capacity to condense water out of the air.

Fog is barely damp. If you wade through vegetation, you can be soaked. Out in the open, a light dampness is more typical. Very light rain gear is all that is needed.

Mist has no perceptible downward motion. Drizzle does. Both can soak a hiker in less than ten minutes. Wear rain gear.

Plain rain falls straight to the ground, with winds less than 25 mph, no hazard, easy to work in. Wind will not drive water through your rain gear.

Real rain is wind-driven; wind will drive water through light rain gear.

A warm storm with five to fifteen inches of rain and moderately strong winds is called a pineapple express, so named for the tropical warmth of the storm, which gathers heat and moisture from the tropical Pacific Ocean near the Equator (and near Hawai'i, hence the pineapple). During pineapple expresses, winds are often 60- 70 mph, rainfall usually exceeds 10 inches, and temperatures are in the mid 50's to mid 60's. Rain gear only tempers these rains. Staying upright can be difficult, even in the lowlands. Hiking is hazardous - stay indoors until the winds pass.

Freezing periods, with or without snowfall, usually end with a storm, during which the first 24 to 48 hours of rainfall freezes to all surfaces, called a silver thaw or ice storm. Beautiful to hike in, but dangerous. Tree limb breakages from ice loads are common. Stay close to home and out of the mountains.

Cold storms with high winds, or howlers, are common. The coast usually experiences at least five howlers each year, with winds over 100 mph and ample rainfall. Air temperatures range from 30's to 50's. If you must be out in this weather, wear industrial-weight rain gear. Conditions can be very hazardous.

Uncommon Weather Events
Occasional ice storms, periods of freezing weather, hurricance-force winds, tornadoes, floods, and storm-driven high tidal surges punctuate typical weather, water levels, and tides. These uncommon events may happen once a year, once a decade, or once a century. In the past century, this area has also experienced frost every month of the year.

Weather Cycles
Coastal weather is strongly influenced by short and long term oceanic conditions. These include one to four year long El Niño-Southern Oscillation events, which bring warm, usually drier weather to the entire Pacific Coast. The alternate climatic condition, so-called La Niña events, bring cooler, and usually wetter weather.

A multi-decadal climatic period, called the Pacific Decadal Oscillation, also cycles between prolonged periods of cool wet and warm dry weather. As of the late 1990s, this area was thought to be reentering a period of cool wet weather, bringing with it better nearshore conditions for salmon, and slightly cooler and wetter winters.

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Physiography

The Coast Range of Oregon and Willapa Hills of southwest Washington dominate the Columbia Coast. This mountain range separates the coast from adjacent interior valleys and waters of the Willamette Valley - Puget Sound Trough. Peaks occasionally rise over 2,500 feet in the Coast Range. Saddle Mountain, the highest local peak, has an elevation of 3,296 feet.

One large and several small rivers dissect the landscape. If sea level was to rise only 200 feet, this region would become an archipelago of a few small and several large islands. The Columbia River cuts through two ranges, and is tidal for more 150 miles upriver, well east of the coastal region.

A wet climate acting on fine sedimentary materials over millions of years led to a high degree of erosion and dissection of drainages. More than four miles of streams per square mile of land is typical throughout the Coast Range. Waterfalls are common where erosion reached hard surfaces in stream valleys, usually subsurface basalts, occasionally sandstone. Perched wetlands, seeps, and springs are common, as well as seasonal streams in the upper reaches of drainage basins.

Wildfire
The Columbia Coast is just north of the line of regular wildfire occurrence on the Oregon Coast, which stops in the Nehalem River Valley. Below this line, both summer climate and landscape management by indigenous peoples led to regular burning of the forests, usually on a 50 to 80 year cycle. Above this line, wildfire is much less common, and therefore more likely to be catastrophic when it does occur.

Landform Alterations
Jetties around the mouths of local rivers and estuaries led to accretion of beaches , resulting in very recent (in geologic time) creation of ocean front lands west of geologically stable shorelines. Even more recently, erosion of these beaches, retrograding back towards historic positions, has led to speculation that the hydroelectric dam system on the Columbia is doing more than irrigating farm land, floating barges and ships, slowing floods, killing salmon and producing electricity. It is also stopping the historic movement of sediments in spring flood waters to the ocean. These regular floods formerly brought new sediments into the Columbia Delta each year.

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Geology

Throughout the Columbia Coast, a river runs through it and basalt provides the foundation. The base rock is Eocene seafloor basalt, 55 to 35 mya, overlain by marine and estuarine sediments, occasionally overtopped by Miocene basalts, 12-15 mya, with infrequent bands of coal-bearing strata and numerous fossils. Most of the headlands and mountain-tops are capped with relatively young Miocene basalt (example: Tillamook Head). Some headlands and hills expose older Eocene basalts (example: Cape Disappointment). Older sedimentary layers range from coarse conglomerates to sands, silts, clays, including sandstone, mudstone and siltstone, and shelly layers, 40-7 mya.

The Columbia River predates the rise of the Cascade Range and the emergence of the Coast Range, as well as the last ice age. It is estimated to be at least 30 mya old, and probably began in the Rocky Mountains as that range began to rise 45 mya. Even when young, this river had enough water volume to cut through the Cascade Mountains during several range-building periods, and then through the Coast Range as it too came up out of the ocean. The river predates much of western Oregon and Washington, and also predates current land positions, showing the effects of millions of years of rotational force and Miocene lava flows, on the land, displacing the river bed northward more than 50 miles from its original straight path to the ocean as it flows around present-day northwest Oregon.

During peak ice-holding periods in the last ice age, sea levels were 300 to 350 feet lower than at present. This resulted in deep canyons being carved out of the coast range and the continental shelf as rivers flowed to the Pacific Ocean. As sea level rose to its present level, those canyons submerged and filled with nearby upland and nearshore sediments, resulting in characteristic flat river valleys in present-day landscapes. Recent alluvial sediments are generally late to post-Pleistocene, including materials deposited in the ocean during a series of floods from waters released from glacial Lake Missoula in western Montana. Current studies of beach and estuary sediments have concluded that most can be traced to historic deposits by the Columbia River into the nearby Pacific Ocean.

Continental ice reached south to the Chehalis River Valley during the Pleistocene, leaving behind signature glacial debris, gravels, thin soils, clay lenses, boulders and ice-slicked rock. The region encompassing the Columbia Coast was below this ice line, and stayed free of continental ice. Collections of boulders and other features of ice sheets can occasionally be found, carried downstream on ice flows during historic floods from glacial Lake Missoula.

One large circulation cell dominates the movement of sediments in the nearshore ocean environment - the Columbia cell, which extends from Tillamook Head in northwest Oregon to Point Grenville on the Olympic Peninsula in Washington. Sediments stay inside the cell, and are available to move onshore and into estuaries when they are in shallow waters. The beaches of Clatsop Plains, Long Beach Peninsula, Twin Harbors, and Ocean Shores are within this cell. Sediments are coarsest around the entrance of the Columbia River, and gradually become finer moving north to Point Grenville.

Black sands, which are dense, dark-colored, and rich in iron and manganese, form beds offshore and on beaches around the Columbia. Light-colored, less dense quartz sands dominate summer beaches. In winter, some beaches are completely black, as quartz sands move offshore into the surf, leaving only the heaviest, black sand grains behind.

The Pacific Northwest formed as a series of island arcs and seafloor sections collided with the North American continent. Seafloor sections are generally accompanied by subduction zones and seafloor growth zones. Nearby Cascades volcanoes are a byproduct of the present seafloor subduction zone plunging under North America, while the Coast Range plate docks against the continent, and new sea floor is produced offshore.

It will be the fate of the Coast Range to crumple up against the Cascades when the current subduction zone finally locks and pushes up the present sea floor to become new land attached to North America. When that happens, the present active volcanoes in the Cascades will go quiet, and a new group of volcanoes will grow up further west in the Coast Range. The Columbia River will have another range-building area to cut though on its way to the Pacific, and another seafloor. In the meantime, the Columbia Coast is occasionally visited by large subduction-zone earthquakes, which are accompanied by liquefaction, subsidence, and tsunamis.

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Time

Coastal rainforest has existed in this area for at least 2 million years, shifting from warm temperate to cold temperate as climate changed. This prolonged period of stability has produced diverse and highly stable communities of plants, despite rises and falls in sealevel, and changes in timberline with glacial and interglacial periods.

Highly diverse refugia dot the landscape, particularly mountain balds where upwards of two hundred species of herbaceous plants can be found. Despite their present small size, these refugia contain several hundred species of wildflowers and grasses in a complex community that was formerly widespread during glacial maxima. High species diversity can usually be attributed to two elements: historic large ecosystem area and relatively low productivity.

In contrast, the present low, alluvial areas along the coast have existed for less than 10,000 years. Rivers and estuaries are older, but as sea level rose and fell, plants advanced and retreated with water levels and shorelines, moving east more than 50 miles in less than 1,000 years at the end of the last ice age.

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Land Alterations

Jetties around the mouths of local rivers and estuaries led to accretion of beaches, resulting in very recent (in geologic time) creation of ocean front lands west of geologically stable shorelines. Even more recently, erosion of these beaches, retrograding back towards historic positions, has led to speculation that the hydroelectric dam system on the Columbia is doing more than irrigating farm land, floating barges and ships, slowing floods, killing salmon and producing electgricity. It is also stopping the historic movement of sediments in spring flood waters to the ocean. These regular floods formerly brought new sediments into the Columbia Delta each year.

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Contact Information

ksayce at willapabay dot org