Fun in the Scablands

In the scablands.  As their name suggests, these are lands that haven't healed.

Try telling friends you went to the scablands of eastern Washington for vacation.  The reaction will be a blank or questioning look and then “Why did you go there?”  Eastern Washington is known mainly for endless wheat fields along Interstate Highway 90, and most people have never heard of the scablands.  Based on the name, they hardly seem a destination of choice.

Geologist J Harlen Bretz was the first to promote the scablands of eastern Washington, in the early 1920s.

The origin of "scabland" often is attributed to geologist J Harlen Bretz, but after reading The Channeled Scablands of the Columbia Plateau (Bretz 1923), I think he was quoting locals rather than inventing a new word:

“The terms ‘scabland’ and ‘scabrock’ are used in the Pacific Northwest to describe areas where denudation has removed or prevented the accumulation of a mantle of soil, and the underlying rock is exposed or covered largely with its own coarse, angular débris.”

Bretz was obsessed with the scablands.  By 1923, he had traveled 3000 miles across eastern Washington by foot and horseback studying, describing and mapping their unique landscapes.  The denudation was extensive -- he mapped some 2000 square miles of bare rock (estimates are now up to 16,000 square miles).  Even more fascinating was the cause of the damage.  Bretz realized it had to have been immense raging ice age floods.

Monster floods were a radical proposal at a time when geologists had rejected catastrophe as the main mechanism of change, favoring instead slow steady processes.  In his 1923 paper, Bretz carefully described the abundant evidence, including 21 scabland features indicative of catastrophic flooding.  In his mind no other explanation would suffice, but he was alone in this view.  Prominent geologists of the day were sure that floods at such a scale were impossible.  In spite of almost universal opposition, Bretz stood firm by his story for 40 years until others finally were persuaded.

An early satellite image (1972) of eastern Washington.  Darker braided areas are scablands, pale areas are mainly wheat, red areas lower left are irrigated fields.  Source.

In the satellite photo above, eastern Washington looks very much like a flood-ravaged landscape with irregular braided, anastomosing channels.  Unfortunately aerial images weren’t available when Bretz was doing his research; he mapped the scablands from the ground (below).

J Harlen Bretz's map of the scablands (1923).  Click on image for larger view.

Today Bretz’s story of catastrophic floods is widely-accepted, and in fact is the subject of nature programs, interpretive centers, many books, a national geologic trail and of course geo-vacations.  That’s why we went to eastern Washington -- to immerse ourselves in damage wrought by ice age floods.

[For more about Glacial Lake Missoula, and the catastrophic floods released when its ice dams failed, see earlier posts in this series.]

Northrup Canyon off the Upper Grand Coulee.

Ice age floods are only part of the scabland story.  The landscapes they carved are composed of basalt -- hard dark coarse rock formed from lava flows.  It's the nature of the basalt that gives the scablands their distinctive look.

Basalt covers a huge area in the Pacific Northwest, though much of it is now buried.  Total extent is on the order of 80,000 square miles, making this the largest collection of lava flows in North America and a certified large igneous province.  Between 17 million and six million years ago, volcanic activity in the Pacific Northwest was intense, especially in the early stages.  In fact most of the lava was produced during the first 1.5 million years, a really short period of time considering the volume.  There may have been as many as 300 high-volume flows (source).  Lava poured forth from linear fissures as far east as Idaho, flowing generally west.  The early eruptions were quite large and the lava more fluid.  Some of it even reached the Pacific coast.

The Columbia River Basalt Group, a large igneous province; from exhibit at Dry Falls Visitor Center. 

By the time of the last ice age, the basalt flows were largely covered with more recent deposits.  Then around 15,000 years ago the megafloods arrived.  Huge masses of water hundreds of feet deep traveling at unbelievable speeds (to 60 or even 80 miles per hour) scraped off grassland, soil and dirt.  The water went to work on the basalt next, sculpting it into the curious landscapes of the scablands.

How could water have carved hard basalt into these spectacular forms?  It’s hard to imagine.  Water can erode all kinds of rock given enough time, but the scablands were created by short-lived floods.  However these were enormous, swift and very powerful floods, with kolks dancing in the torrents -- underwater tornados ripping up basalt!  They easily took advantage of inherent weaknesses in the rock.

When a thick basalt flow hardens into rock, the inner part cools more slowly, and shrinks and cracks in regular patterns, generating striking sets of columns.  In contrast, lava near the surface of the flow cools rapidly; fractures are irregular and discontinuous.  These two zones are called colonnade and entablature.  It was the beautiful colonnades that were exploited by flood waters.

Highly-simplified diagram of several basalt flows showing colonnade and entablature.

The real thing -- colonnade and entablature downstream from Dry Falls.

We found beautiful columns in many places -- like these at the end of Deep Lake near Dry Falls.

Remains of columns line the Deep Lake parking lot.  They’re most often hexagonal, but not always.

It’s perhaps surprising that colonnades are the weaker zones, since entablature is more fractured.  But entablature fractures are irregular, discontinuous and not as “penetrative” whereas those of colonnades are long, continuous and deeper.  Powerful floodwater can readily pluck out column pieces.  Eventually the overlying entablature collapses.

Huge fallen fragments of entablature.

Colonnade under overhanging entablature in Northrop Canyon, accessible via a very pleasant hike.

It's wonderful to tour the scablands and marvel at scenery created 15,000 years ago by monstrous raging floods.  Landforms range from curious to spectacular, and most are easy to spot and understand.  Here are some of the ones we saw.

“Butte-and-basin” or scablands topography

There is a distinctive style to scabland landscapes, due to the resistant basalt and the way it was eroded -- by plucking and collapse.  The channels, buttes and ridges have steep sides, and the channels often are fairly wide, with relatively straight sections.

Scablands topography at Deep Lake, which sits in a large depression carved out by floodwater.  View from a hike in Sun Lakes-Dry Falls State Park.

Near Dry Falls we hiked across and around Umatilla Rock, a narrow ridge left standing where flood waters split into two channels after the big plunge (below).  This is another good place to view colonnade and entablature.

Trekking through scablands near Dry Falls.  Trail passes through smaller notch near left edge of photo.

One late afternoon we scaled Steamboat Rock, a scabland butte.  The trail climbed through multiple basalt layers to the top where we found ... erratics left by glaciers!  Steamboat Rock was covered with ice when a lobe of the Cordilleran ice sheet extended far south.  There also are glacial moraines on the summit.

Steamboat Rock.

View from the trailhead; note multiple basalt flows.

Communing with glacial erratics on the summit -- some kind of granite-like rock.

Coulees (COO-lees)

Looking across the Upper Grand Coulee.  It was dry until the 1940s, but now holds the waters of Banks Lake.

"Coulee" evolved from the French word for flowing, but most coulees in the scablands are dry (or were before being filled with water by engineers). They differ from those elsewhere in North America.  These are giant flood channels, often cut where none existed before, and so aren’t typical V-shaped mature drainages. The bottoms are wider and the walls steeper.

Above is Dry Falls in the Lower Grand Coulee.  The rim is 3.5 miles across, much wider than Niagara Falls.  At peak flood, the surface of the water is thought to have been 400 feet above the rim, and the “falls” probably were more like big bumps in flowing water.  Today the coulee is dry.  The ponds in the old plunge pools are fed by springs.

The Visitor Center at Dry Falls is highly-recommended, for both the views and the helpful information in the displays and bookstore.  You can camp nearby at Sun Lakes-Dry Falls State Park and explore scabland landscapes by driving, hiking, boating and swimming.

Dry Falls Visitor Center sits on the very edge of the coulee.  Views are terrific.

Hanging valleys

Sometimes when large coulees were carved out, existing drainages were left stranded above, creating hanging valleys.  All the ones we came across were dry (it was mid-September).  It would be neat to catch them when they’re flowing and watch water fall down the steep basalt walls into the coulee.

Below is a hanging valley across the Upper Grand Coulee from Steamboat Rock.  Note green patches of vegetation on steep slope below -- perhaps due to seepage from the valley above.

Depressions, potholes and kolk lakes

Holes dug by wildly-dancing kolks in the flood waters were the most fun scabland features we visited -- beautiful lakes, curious caves and mysterious openings.  They are worthy of a separate post ... to follow.

Evening at Rainbow Lake.

At this kolk lake I met up with what looked to be the Creature from the Black Lagoon!

This post is part of a series about the Ice Age Mega-floods of the Pacific Northwest.

Sources

Allen, JE, Burns, M, and Burns, S.  2009.  Cataclysms on the Columbia.  Portland State University, Ooligan Press.

Bjornstad, B.  2006.  On the trail of the ice age floods.  Sandpoint, ID:  Keokee Books.

Bretz, J Harlan.  1923.  The channeled scablands of the Columbia Plateau.  J. Geol. 31:617-649.