Mina Mounds and why not knowing the answer is a good thing

So Geoff and I were driving down I-5, transiting from station S050 to W070 when we saw the sign for Mima, Washington. “Oh!,” Geoff cried, “Let’s go see the Mima Mounds!”

“Sure.”

So we barrel our way across yet another beautiful valley in Western Washington to find the Mima Mounds. What we saw reminded me of why I became a geologist, and not, say, a physicist.

Don’t get me wrong-I love physics. I teach it both because I like the subject and because it exemplifies the purpose of science education: process over fact. Father Guido Sarducci famously noted that all most people recall from their physics classes was “F=ma.” Alas, all too true. Alas, this is our, the teachers’, fault, not the students’. We teachers need to show our students the beauty of process.

I love doing geology because it’s so easy to see, talk, learn, argue and discover process-to figure out how things are made. Geoff and I drove up to the mounds in the mid-afternoon of a mid-February day and after negotiating a sign-laden road came to a flood plain covered with round hills six feet high, 20 feet across and 100% unexplainable. Geoff and I both started talking at once, just noting our observations and opinions as they came to us: the mounds weren’t uniformly high (1 to 6 feet, mostly 6); they weren’t uniformly shaped; they were, then we decided were not, then re-decided they WERE, packed in a geometric arrangement. Then we started discussing previous hypotheses of their formation, which Geoff had somehow remembered reading about 17 years earlier. (Like most good scientists I know, Geoff devotes a substantial amount of brain space to worthless information. For him it is the lyrics to bad late-70’s songs; Kip knows the scores of UNC basketball games; Jim knows the words and music to an amazing number of television shows and ads.)

Soon we were digging into a mound, noting that the top of the mound contained a horizontal layer of black, loamy, organic soil, while the lower parts of the mounds were lighter and coarser, with a gravelly texture. We both thought the idea that the mounds had been formed by gophers possible but unsupported; we resisted the seismic solution that the mounds formed as nodal points during earthquakes, and rejected out of hand the giant ant idea. We then moved backward to discussing whether the mounds formed from something being deposited, or from something being eroded. Finally we climbed a small observation tower to get the global view. (If you ever get to Mima Mounds Natural Area Preserve, read the interpretive material at tower-it is unusually well done.)

The airphoto to the left (of unkown provenence) gives an even better view than the tower. It shows that the mounds have a maddeningly similar but not identical structure. Note how many (not all) the mounds have tails that lead to another mound or an interstitial space between mounds. Where the tails separate mounds, the mounds are perfectly aligned; where the tails…well, you get the idea.

Geoff and I have spent the last hour trying to find more information on a sloooow connection here in Enumclaw, and as he just said, “I will continue to be baffled by the Mima Mounds.” Not knowing the answer, but having tried to figure it out, is what science and science education should be about. Sure we don’t know yet what is going on here (and in other areas across the US and the world where similar mounds are found), but we have a good list of what isn’t responsible. In this case not knowing the answer is great.

A friend of mine might describe the hubris Geoff and I displayed during our visit as just one more example of professorial presumption. How could we, knowing little about the mounds, have an opinion about their formation? Well, because we have a decent knowledge of the processes that shape the earth, and we aren’t afraid of being wrong. We chunked through a dozen hypotheses, each rejecting the other’s ideas, until we had eliminated everyone we could think of. Then the real work started-what hadn’t we thought of? What data did we need? Sure, you can do this with physics, if you happen to have a $4 billion proton-antiproton collider with a 8 story tall scintillation counter. Don’t get me wrong-I love the search for the Higg’s Boson. It’s just that I can’t do it while driving across town on an errand.

Romancing the seismometers

Yesterday’s post introduced the whole point of this trip: science is a constructive process, whether you are doing it or teaching it. Today’s post focuses on the practice of science…both the romantic bit about walking 2 miles in to a site with snowshoes only to realize there’s a snow-free road coming in from the other side, and the unromantic bit about how dehydration of amphibole at 100 km depth is no longer the accepted explanation for the volcanic front at subduction zones. The explanation of the first observation is easy (our maps were right but they didn’t have the most recent data); the explanation of the second observation is not easy (although it also has to do with not having the most recent data).

So first the romantic part. Geoff and I have been checking up on some 60 seismic monitoring stations he and his colleagues have deployed in western and eastern Washington. Geoff and his colleagues aren’t interested in the earthquakes themselves-they’re interested in the sound-the seismic waves-these earthquaked produce. As we’ll discover, these waves act much like x-rays in a CAT scan, revealing the detailed structure of the earth. In a CAT scan, the machine provides its own x-rays. In the earth, we need to wait for earthquakes. A lot of earthquakes. A CAT scan takes a few uncomfortable minutes-recording enough earthquakes to map the structure of the earth takes many years and many seismometers.

Our task this week is to go to each seismometer in the network and give it a 100 day check up. The stations are pretty basic: a buried seismometer measures ground motion 50 times per second, then sends this data to a mess of electronics in a glorified Styrofoam cooler. After some fascinating filtering and data compression, the record of ground motion is recorded on 2 Gigabyte flash drives. The whole apparatus is powered by truck batteries and solar panels. The arrangement of parts at a station works great. A few stations have required more maintanenace, mostly because people with rifles somehow mistake the metallic blue solar panels for dull brown deer. For the most part, though, the primary enemies are snow and insects.

The check up itself is generally a brief affair, involving a checklist and the careful swapping of flash drives. The thoroughness with which we do this work is surprising, until you consider that this thoroughness is essential if the data are to be free of systematic error. Good data requires significant energy.

My favorite part of the 15 minute routine is checking to see if the seismometer is working. Geoff hits a button on a PDA, and I start tapping my foot on the ground a few meters from the seismometer. In a few seconds, the PDA displays the seismometer’s output, with a clear record of the shaking I have induced in the earth. The key is to constantly invent a new way of making the ground shake in a pleasing way. Geoff has the best so far: A metal pole near one of the stations produced an exceptional example of a decaying exponential signal with a super-imposed 2 Hz sinusoid I’ve ever seen. Alas we can’t download the data, or I would share it with you!

The array of stations begins nigh on the coast near Ocean Shores, Washington and then fans out over most of the state. At Ocean Shores we could actually hear the surf, and see the surf on the PDA display. A mile from the beach, the seismometers recorded a lovely 3 second period to the noise. As we moved eastward to Copalis and then Humptulips (really), the surf noise lengthened to 6 and then 12 seconds. Even 60 miles inland, with the beach far out of earshot, the seismometers dutifully reported the earth’s propagation of surf noise to the outskirts of the Olympic Mountains.

The seismometers work best in quiet environments far from frequently traveled roads, but they need to be placed in a pattern optimized to give good results, and close enough to a road so the 300 pounds of equipment can be lugged in by foot . (This map shows the layout of the seismometers as black circles.) This combination of requirements means we spend a lot of time in clear cut forests managed by the Department of Natural Resources. (Yes, clear cutting is pretty destructive, and it does mar the landscape and ecosystem. WE’ll return to this topic!) We spend many, many hours every day driving along the best kept logging roads in the world. For the most part, the Department of Natural Resources of Washington does a great job of keeping these roads cleared and graded-even during winter. Yesterday afternoon, after driving for about an hour into the Black Hills at Capitol State Park we ran out of road. well, we actually ran into a few feet of snow, so after digging out the ridiculous SUV we rented, we put on our snowshoes and walked in the last 2 miles to the station. We’d been walking for about 30 minutes or so when the forest opened up to reveal the crater of Mt. St. Helens staring at us. (How could we see into the crater? Because it looks like it is missing. Because it is missing. Where were you in May of 1980?) Sure, it was only 70 miles away, but still,it was so BIG. Oh, and there’s Mt. Adams, oh and over to the left Mt. Rainer. A trifecta on the last station of the day. It made the fact that you could drive into the station from the other side much less painful.

Tomorrow: The Mounds of Mima and why the volcanoes I just mentioned all line up. Mostly.

Window seat, left side, rear of the aircraft

The second most common question students ask in science classes is “How do we know that?” Good question, tough answer. Good because “how” is what science education is-or should be-all about. Tough because the answer to the question often involves exactly the science and mathematics the student has yet to learn.

 

Constructivist and inquiry based learning were designed to address this dilemma. Constructivism is the (excellent) technique of learning by constructing new understanding upon established knowledge. Inquiry is the process of discovering information through guided discovery. They are complimentary approaches, and emphasize understanding of science as a unique and valuable way of understanding the universe, as opposed to a list of facts easily recited, and forgotten, on a multiple choice exam. Ironically, the best aspects of learning science exactly reflect the best parts of doing science-it’s a constructivist process. The project I’m working on this week is the result of literally 50 years of people learning something new by asking “why does that happen?”

 

Over the next week I’ll be answering the “how do we know that” question first hand. I’m off to the Pacific Northwest to help out a friend “service” a deployment of 60 seismometers spread from Copalis Beach to Enumclaw, Washington. As we’ll find out, this kind of work isn’t obviously sexy, but it sure is fun. And illustrative, both of how hard it is to do science right, and how hard it is to teach science right. First, though, we have to get from Kansas City out to Shelton, Washington.

“That”-what we know-is the structure of the earth from the surface down to about 60 mile depth. Driving 60 miles across the earth takes an hour, but getting 60 miles deep is impossible. It’s important to remember that we have no first hand experience with the structure of the earth below about 3 miles down. The deepest mine on earth is only 2 miles deep, and the deepest hole ever drilled is a mere 9 miles deep! So all our knowledge of earth’s structure comes from remote sensing, largely from the study of the waves released by earthquakes and subsequently reflected, refracted and twisted as they travel thorough the earth. The quick answer to the question of how we know earth’s interior structure is simple: careful interpretation of subtle differences in the way earth transmits the sound waves generated by earthquakes. Of course, that kind of answer is the same thing as saying babies come from the hospital.

 

The details of all this are where the fun is, and this week is all about sharing the fun with you. Even the flight is worth sharing. Heading west northwest from Kansas City toward Seattle provides the greatest geological cross section of the continent one could hope for. Kansas may well be flatter than a pancake, but a slight dusting of snow brought out the boundaries between the wheat fields, divided by the USPLSS into quarter-mile packets set between orthogonal range roads. (The USPLSS is a wonderful testimony to rationalism, Jefferson, and hubris. I love everything about it. Read all about it.) By the time we got to western Nebraska, the snow had begun to bury those same range roads, and the fields had grown to a mile across. (Fewer people, larger farms.) We left the plains behind at the Wyoming border, and anyone can tell that the world has changed. The checkerboard fields had disappeared , replaced by the hogbacks, flatirons and hanging valleys of the Grand Tetons. The Midwest, geologically quiet for 250 million years, was gone, replaced by an active noisy continental margin.

 

Just over three hours north west of Kansas City, I looked back towards home and saw that all the gullies, streams and rivers were heading back the way I came. Ahead, all the water pours westward-the continental divide. We all know water flows down hill, but the hills here point in different directions, due in part to the complicated mixture of forces acting on the western edge of the continent. Then the checkerboards reappear, stuck in long, flat valleys of sand crammed between mountain ranges, a sure sign that we have left the Rockies for the Basin and Range province. Then the first volcanoes show up, a sure sign that we are in a new world yet again. These first cones are stubby and squat, barely rising about the low ground fog forming in the late afternoon sunlight. The view is oddly martian-the stationary clouds hover at the edges of the mountains like a Harryhausen special effect-cool, but not quite real. Think about it-just a few hours from Kansas City and I’m flying over earth so hot that molten rock made it to the surface. Why there and not KC? Why when we reach the Cascades is there a line of volcanoes-no longer stubby and squat-stretching south toward California?

 

This last question-why are the Cascades where they are, how does the earth melt to form these things and how do we know it are for tomorrow.

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