The Blue Planet: Geology and the Pacific Northwest

Notes from the 2nd class of the Big Ecology Conservation Course by Course Volunteer Bob Herbert
The second night of the Conservancy’s Big Ecology course was a fascinating presentation by Alan Gillespie that revealed the dynamic geology of earth.  Like all disciplines in science these days, geologists continue to revise and hone their understanding of how the planet came into being, and how it has changed over time.

            

Basalt in the Columbia River

We learned that rocks are divided up into three categories: igneous, sedimentary and metamorphic.  Igneous rocks are created through the recycling action of volcanoes.  Granite and basalt are both examples of igneous rock.  As tectonic plates collide, the heavier one will dive under the lighter.  As the rock gets forced downward into the mantle of the earth it melts the leading edge of the plate and through a volcanic eruption, it reappears on the surface as lava.  

             

Sedimentary rocks are created through a layering process.  For example, layers of sand build up through wind and rain erosion and with time and pressure they form sandstone.  When sandstone is exposed to the elements it erodes into beautiful and delicate hoodoos and arches, and Utah and Arizona are filled with amazing examples of these.

             

Metamorphic rocks are formed under intense heat and pressure.  Some of the rock crystallizes, while other parts become warped.  When these rocks are exposed, they show banding that is curved and distorted, instead of linear. 

             

We discovered that geology is no different from other disciplines of science in that its origins were found in stories and legends.  These legends served as factual science for the people of that time period and geographic location.  The legends transformed over millenniums, and now they are nothing more than humorous stories about our ancestor’s lack of scientific knowledge, but for a long time this was how science was taught.  One of the main things that these stories provided was a process for how things worked.  It didn’t necessarily have to be correct to sufficiently explain a natural process that people wondered about, like the sun rising and setting every day.  Science is the modern outcome of these campfire stories, and science continues to improve and adjust its understanding of the world we live in.

            

The discovery of radiometric dating opened the door for geology.  This process measures the amount of Carbon 14 found in a rock and through a mathematic equation, the age of the rock is determined.  This discovery allowed geologists to measure the ages of various layers of rocks and fossils and through this data our modern understanding of earth’s geology and plate tectonics was born.  Carbon dating has confirmed that the earth is 4.55 billion years old.

            

The Earth is made of a "core," "mantle," and "crust"

When the earth was originally forming, the heaviest elements sank to the center, which is how our super-heated iron core came into being.  Uranium is found in the transition into the outer core and mantle, and the earth’s crust formed as the surface of the liquid mantle cooled.  Scientists believe that our moon was actually a large meteor passing through our solar system and it slammed into the side of earth.  A portion of earth broke off and the remnants of this collision went into orbit around the planet, giving us our moon.  At the same time, the collision tilted earth’s rotational axis.  It is this tilt that provides the four seasons for our planet.  If earth’s orbit around the sun was perpendicular instead of being tilted at 23.44 degrees, then the weather at your home would remain the same year round.       

             

The rotational velocity of earth (approximately 1,000 mph) combines with the electrical field that surrounds the inner core, and together they create the dynamo that produces the dipolar magnetic field which protects earth from cosmic radiation.  This phenomenon not only provides earth with protection from solar radiation, but it also provides us with magnetic north/south for navigational purposes.  The Van Allen belts are the name of this magnetic field and they are also responsible for the northern lights.              

             

By studying fossil records geologists have confirmed two major extinction periods that occurred 250 million years ago and 65 million years ago.  The oldest is named “Snowball Earth” and it was a massive ice age that covered the entire planet with snow and ice.  As the glaciers receded toward the poles the age of the dinosaurs slowly began.  Giant reptiles dominated the surface, air and oceans until 65 million years ago.  At that point, a meteor is thought to have hit the earth and the dust from the impact blocked out the sun long enough to drive the dinosaurs into extinction.  We are currently living in another period of mass extinction (right now nearly 20,000 species of animals and plants around the globe are considered at high risks for extinction), and unfortunately, humanity seems to be the cause for this one.

             

300 million years ago there was one supercontinent called Pangaea

Geology took another leap forward when it was determined that the continents were joined together about 300 million years ago in one supercontinent named Pangaea.  The crust floats on top of the liquid mantle, and over time it broke into pieces. Over millions of years they drifted apart from each other and created the continents as we know them.  Geologists determined that oceanic plates are heavier and continental plates are lighter, and they are all in motion.  Fault lines have been created where these plates have come together, and when these giant chunks of earth slip against each other they create earthquakes.

             

Even though North America and Asia appear to be seamless pieces of land, they have actually been created through a series of smaller pieces slamming into the larger, main piece.  India is a perfect example of a smaller piece of land crashing into a larger one.  The point of contact for India was in the north and the collision with Asia created the Himalayas.  We also learned that the west coast of North America was not part of the original craton (an old part of the continent), which broke off from Pangaea.  The Rocky Mountains were created when a piece of land drifting east across the Pacific Ocean slammed into the older bit of continent.  The Pacific Crest is another example of how a collision between two plates produced a north/south oriented mountain range in North America.

Another geological discovery that helped explain earth’s ever-changing landscape was hot spots.  The Hawaiian Islands are the most obvious example of this.  Kauai was the first island to form, but as the crust shifted over the hot spot in the mantle, another neighboring island formed, and so on.  This is why the only island with an active volcano is the Big Island, because it is the last island to be created, and it currently sits on top of the hot spot.  We learned that Washington was also over a hot spot at one point in its history.  The basalt created in the Columbia River Basin was from the same hot spot that is now underneath Yellowstone National Park.  The amount of volcanic material (basalt) deposited in Washington from the hot spot was approximately 80,000 times that of the eruption of Mt. St. Helens, and that same plume of heat now drives the geysers and hot springs of Yellowstone.

             

Once all of the big pieces of the west coast were in place, then a combination of volcanic activity and glacial erosion created what we now know as the Methow Valley.  Mt Robinson is actually one of the dividing lines between continental rock and basalt (volcanic) rock.  A quick glimpse on Google Earth confirms the rock to the west of the peak is charcoal grey eroding basalt and the rock to the east is lighter and granite in appearance. 

The upper Methow is U-shaped because it was carved out by glaciers.

The upper valley (Mazama & Lost River) was formed as a result of a glacier 7,000 feet thick that covered the North Cascades, and it began receding 17,000 years ago.  The shape of the upper valley in the Methow is “U” shaped which is indicative of glacial erosion.  Below Carlton, however, the erosion becomes “V” shaped, which indicates erosion from water runoff alone, so the Methow was actually formed by two different geological actions.

The northwest is rich in volcanic nutrients and boasts enormous biodiversity.  The Cascade Range is a wonderful combination of plate tectonics and volcanoes, glaciers, forests and rivers, and thanks to Alan ’s expertise, we all have a better understanding of how the magical Methow came into being.