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TIDE

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High and Six Hours Later - Before and After

 

-----Once upon a time, I taught Oceanography. Oh, don't get the wrong idea - I'm a geologist. But one semester. our department had a Visiting Professor who was an oceanographer. His introductory course was packed with students, even in our landlocked state of Nevada. When he departed and we could no longer teach the subject, our Chairman was distraught. To me, a teacher, I thought he was upset because our students wouldn't have the opportunity to learn the field. No - I'm much too naïve. He was upset when our visitor left because our departmental budget was determined by the number of students we taught and lots of dollars just went out the door.

-----This demanded a bureaucratic solution - he held a departmental meeting. What were we to do? In typical committee fashion, the department decided that since I was a water geologist and had once owned a boat, I would be the one to teach Oceanography. The fact our boat had only been on fresh water and that I'm a desert region ground-water hydrogeologist had nothing to do with the wisdom of their choice, as they saw it. So I became the resident oceanographer. Fortunately for my students, I demanded, and the department grudgingly acquiesced, that they would fund whatever training I thought necessary to equip me to teach Oceanography.

-----So, I attended some great graduate courses by outstanding profs at Scripps and had the opportunity to join them on research cruises - and I taught Oceanography. Tides, however, were a mystery. Oh, I understood that the gravitational attraction of the moon would pull the liquid water of earth's surface toward it. This slopped the water of the World Ocean toward the side of the earth that faced the moon. This made a high tide, and the other areas of the ocean, bereft of water, would have a low tide.

-----OK, easy enough. But, then the questions. "Earth rotates every twenty-four hours. What happens to the bulge of the high tide?" I began with an easy question.

-----"Well," the Prof explained, "the bulge stays put, dutifully facing the moon, and the earth rotates under it". Hmmm. Well, that took a little imagination, but OK, I got it. So, at any one place the tide would be up or down depending on whether or not it was facing the moon. Fine.

-----"What about the sun?" I continued my questions. "It has a gravitational pull …"

-----"Well, when the moon and sun line up, it makes an especially big tide, and when they are at right angles to each other it reduces the height of the tide," came the answer. Hmmmm. OK, I could visualize that.

-----Now I tossed out the biggie. "Hey, but there are often two high tides per day. How could that be, if there is only one moon attracting one bulge to one side of the rotating earth?"

-----"Well", my oceanographer Prof said, "there are two bulges - one facing the moon and another directly opposite. The low tides are at the right angle positions from the moon." Whoa! There's what? Sure, I had seen those marvelous diagrams showing the high tide facing the moon and a high tide on the other side.

-----Then I lofted the one-word question Profs either most loved or most feared (depending on the ego or knowledge of the Prof). "Why?" I asked, and watched him grimace. I continued, "Why the bulge on the opposite side? I don't get it."

-----"Well, there's this stuff in physics about angular momentum and … well … you see, the moon also pulls the solid earth toward it and that leaves some water on the opposite side left behind as a bulge … and … well … ah … class dismissed".

-----The next day I brought up the two tides again, to the obvious distress of the professor - nothing worse (or better) for a Prof than to have another Prof in his class (again depending upon the Profs). Anyway, we got tangled up in esoteric physics and finally he just decided that the second bulge? … "Well, it's just there."

-----OK. But, then I asked why some coasts have only one high tide a day and others had two? And, how come high tides everywhere aren't the same height, since the moon has a constant mass and hence a uniform gravitational attraction? After a long thoughtful pause, he said, and I quote, "Damned if I know," so we forgot tides and moved on to oceanic currents.

-----I even pursued a tidal expert at Scripps and he had to admit that if we didn't know past tides at a location, it would be quite impossible to predict future tides. "Even if we knew bottom topography, and such?" I asked, "… and moon and sun phases, and … and everything?" I asked.

-----"Impossible," came the learned reply.

-----So, there you have it. Tides are a mystery. The simple explanation of the moon and the sun is easy, and everything else gets tough. Suffice it to say, that tides usually behave predictably. Since we know the past record of tides, it's relatively routine to predict the future times and heights of tides. I think of it sorta like being with El. We have been together over forty years, and I usually know what she'll order for breakfast - but once in a while, she'll send me a looper. If tides could talk, I'd get the same answer from them as I do from El -"Not always!"

-----We had some days in Maine when the tides didn't behave. Perhaps because there was a hurricane offshore over George's Bank, or, maybe, because … Anyway, on a gray stormy day, we carefully plotted our journey through the two Hell's Gates of the Sasanoa River to coincide with slack low. The Sasanoa is famous along the coast - it connects the Kennebec and the Sheepscot Rivers, and creates an inside 'sneak' that's nice to use when the ocean is pounding on the outside. Now those two big rivers are tidal - each with a slightly different tide than the other - so the narrow, twisting channel of the Sasanoa Inside Passage is wildly tidal, as any coastal Maine sailor will attest. Sailboats under full power, through the Hell's Gates, will have a 'bone in their teeth' plowing five knots through the water at the same time their infamous 'speed over ground' shows two knots backwards. Locals like to have a picnic lunch along the shores of the Gates at mid-tide and watch the sailboats 'from away' pirouette and curtsey like a ballerina gone dervish.

-----We didn't have to wait for slack tide - Halcyon's engines could force us through - but bear with us ex-sailors. You'll forgive us when you know Halcyon had previously traversed the Sasanoa three times with full mid-tide raging (and, I must admit, it was fun to bash those big waves, whirlpools, and currents). This time, though, we were trying to slide through just ahead of a gale, so thought we had enough on our plate without tempting the Devil. Anyway, we rode the last of the tide westbound when El noticed that the usual ten-foot intertidal wet zone wasn't showing on the rocks - if fact, there was only four feet. "Yikes, what happened to the tide," she said, over the engine's roar.

-----"Beats me," I answered, essentially quoting my old Scripps Profs.

-----In a moment, we and a windmilling slack-tide sailboat, found out. The low tide was high and the high tide was - well, HUGE! It looked like the entire Atlantic Ocean was trying to squeeze into the Sasanoa. We slammed the throttles forward, gripped the wheel, and held on. The sailboat was last seen somewhere between Hell's Gates, trying to lower sail and get the diesel going. It was whirling, dancing, spinning, and heeling like a kid's kite in an afternoon storm. I would not like to have paid their bar bill that night. We made it through fine, thanks to Honda technology, and now we have an answer for those Profs - "The Devil makes the tides."

You get a nosebleed going up the ramp

A big step at the low

-----Maine folks aren't easily impressed - or if they are - they seldom show it. We were fueling at a dock in Penobscot Bay, when the chap noticed our Oregon registration - "OR? What's that registrat'n?" he queried.

-----"Oregon," El answered, a laconic New Englander herself.

-----"Wayah's that?" he answered. "Up in them Maritimes, or sumpin?"

-----"Pacific coast," said El.

-----"Lordy, ya musta cruised a cuppla rocks to git hyah," he said, topping the tank. "My Daddy all-as say-ed, them lil' bots run the longest course."

"Cruising a cuppla rocks"

-----Later in our cruise, we were in a pub visiting with local boaters. "Bin up any of our rivahs?" asked a portly fellow in a red and black checked wool shirt. He was surrounded by his drinking buddies and here was an opportuinity to have some fun with folks 'from away.'

-----"Yes," El answered. "We like cruising rivers. Been up some of them." She took a sip from her beer and stared him down.

-----"Up some of them?" he said with a smile to his friends. "The Kennebec for showah, but what 'bout the Penobscot?"

-----"Had lunch in Bangor," El said.

-----"The St. George?" He frowned.

-----"Yes, to Thomaston, also for lunch," El answered.

-----"The Damariscotta?" he continued, this time with a grin.

-----"Another lunch cruise," El said.

-----He lost his patronizing grin and he faced El directly, beginning to take her a little more seriously. "And anch'rin'? Bin in the Oven's Mouth?"

-----"Yep, pretty spot," El said, continuing to sip her beer. "Tide only runs one way in there - fast."

-----"How 'bout The Basin?" he said, with a feeble smirk to his buddies.

-----"Both of them," El answered.

-----"Both?" The smirk was gone. "You know about the one on Vinalhaven, and been in they'ah?"

-----"Last night," El said, finishing her glass.

-----"Lordy, last night was a moon tide." He had now lost his cool.

-----"Yep, bit of a waterfall going in," El said with a smirk to his buddies. They bought the next round.

THE BASIN

Looks a little rocky

Maybe lumpy, too

Yikes!

(10/02)

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