Reflections on the “history of geology” (not “geologic history”):  Fifty years ago   this year, I began my first college geology course.  By the time I graduated, I had still not studied, nor even heard of, plate tectonics, continental drift, sea-floor spreading, mid-oceanic ridges, subduction zones, Pangaea, or iridium layers.  We had heard no explanation for why the eastern coastline of South America looked like it should fit perfectly into the west coast of Africa on every globe.  Not until 1969 did I read about some of those topics, not in one of my graduate school courses, but in an issue of Scientific American that was devoted to new discoveries in oceanography. 

So, concepts that every 5 year-old dinosaur fanatic or adult viewer of PBS or TLC can now discuss in detail were completely unknown to most geology students in the 1960s.  As a college senior, I used a textbook for a course in Regional Geology that was originally published in 1929.  I even wrote a term paper for the course on a “geosyncline,” the now 100-year old concept that predated plate tectonics as a global/regional explanation for the formation of mountain ranges.  Meetings of the Geological Society of America, the American Association of Petroleum Geologists, and the Society of Exploration Geophysicists were still heatedly arguing during much of the 1970’s about the validity of those new concepts. 

 
Only over the past 30 years have all the pieces of the global plate tectonic puzzle fallen into place.  Now the explanation seems so logical that most people visiting a museum of natural history "to see the dinosaurs” don’t have a second thought when they see videos of black smokers along the Mid-Atlantic Ridge or the Pacific Plate being subducted beneath the North American Plate.  Yet all those advancements in the science of geology occurred during my professional career.  Amazing!

What brought these memories flooding back was a used paperback book I just bought on Amazon.com for our trip to Alaska.  The book is entitled “Banff National Park: How Nature Carved Its Splendor” and contains road-logs and photos of the geology of Canada's most famous national park.  The problem is that the book was published in 1977 and never mentions plate tectonics or continental drift.  Page 22 even shows diagrams of the geosyncline that formed the Canadian Rockies.  The following page clearly states: “For reasons we do not yet understand, the trough area was then severely compressed so that the rocks in it were folded and broken.”  Now, folks, the Lesson for Today: 1) don’t buy geology books from the 1970s expecting to find explanations based on plate tectonics; 2) don’t buy a more recent book on geology that doesn’t have the terms “plate tectonics” or “continental drift” in the table of contents or index, and 3) not all Amazon used books are worth even $2.39 + $3.99 for shipping!

Why belabor the newness of plate tectonics and continental drift?  Because all of the bedrock geology you are seeing on your Alaska trip is explained by these recent concepts.  You are traveling to Alaska along the old western margin of the North American Plate.  In some areas, you will be driving on an ancient “island arc” the size of Japan that crashed* into that Plate.  When you look at your Alaska map and see the long Alaska Peninsula curving away to the southwest and transforming into the Aleutian Islands, you are seeing a modern volcanic “island arc” sitting on the boundary between two plates. And, when you reach Homer and view Mt. Redoubt, Mt. Iliamna, and Augustine Volcano across Cook Inlet, you are looking at part of the “Ring of Fire.”  That ring is the circle of volcanoes marking plate boundaries that surrounds the entire Pacific Ocean and causes the earthquakes that frequent Japan, Chile, Indonesia, Nicaragua, and, yes, Alaska.   When you visit Anchorage, Seward, Portage, Kodiak, or Valdez, you will be seeing cities and towns nearly destroyed by the Good Friday Earthquake of 1964 and its subsequent tsunamis. 

 

When you drive the Icefields Parkway through Banff and Jasper National Parks, you will be viewing a deck of cards pushed eastward for the past 70-100 million years, sliding over one another due to the pressure from crumpling island arcs riding up over the edge of the westward-drifting North American Plate.  When you visit Denali National Park and attempt to view Mt. McKinley through the clouds, you will be looking at the result of one plate ramming another at an angle that pushed up the highest mountain on our continent.  So, you are seeing geology that had no good geological explanation until the theory of plate tectonics became widely accepted.

* “Crash” is a relative term.  Think of two fully loaded semi-tractor/trailer trucks in a head-on collision where you throw away the stopwatch and pull out a calendar.  At a rate of an inch a year, it may take several decades for the two trucks to finally come to a complete stop!  We are talking geologic time, not human time, in the collisions of tectonic plates.