Nature Notes: The World Is Spinning

We are slowing down a smidgeon with each passing year

You’re spinning, I’m spinning, we’re all spinning. Everything is in motion. If you are standing in an island in an ocean transected by the Equator, you are moving easterly at more than 1,000 miles per hour. You just don’t feel it or notice it because the island, the water surrounding it, and everything on it are moving at the same speed. If you are standing upright and motionless on one of the poles, north or south, you are near stationary, except that you turn completely around once every 24 hours. From infancy to old age, you and I, assuming that we have been in the same neighborhood all of these years, have been moving easterly at almost the same speed, but not exactly. 

We are slowing down a smidgeon with each passing year. We in America are very, very slowly drifting westerly, an effect of continental drift. This fact was brought home to me a few years ago when William Walsh, a longtime Montauk surveyor, informed me that one of the geodetic monuments in Montauk that he has been referring to for ages has been moving westerly at much less than one millimeter per year. It is fastened to the Earth’s crustal plate, which has been moving away from the Eurasian plate for millions and millions of years.

Nothing is completely standing still. While the tectonic plate moves beneath our feet, water has moved up and down ever since the Earth began receiving it, according to one theory, from the impacts of comets that are largely made of ice. The tides have been rolling in and rolling out as long as there have been expansive seas. They move in the form of waves, but even when the water is dead calm it is rising up or down depending upon the gravitational pull of the moon. When the moon is full and bright or new and we can’t see it at night, it is pulling on the seas, causing them to rise. 

But the moon is also pulling on the Earth and vice versa, so that the Earth is moving toward the moon as well, and moving away from the seas on its opposite side, causing a bulge outward — a rising tide. When the moon is lined up between the sun and the earth, the gravitational pulls on the three bodies are maximized and we get our highest high tides, called spring tides, and our lowest low tides.

We see the full moon in all its splendor as it rises up, but those beings on the opposite side of the Earth don’t see it because it is in the Earth’s shadow, and vice versa, when the full moon is on the opposite side of the Earth from where we stand. Fullness and darkness occurs roughly every 24 hours, thus there are two high tides and two low tides in a day. They are called semi diurnal, or twice-a-day, highs and lows. The Atlantic and Pacific Oceans both have semidirurnal tides. But the Gulf of Mexico, which is sorta halfway between the Pacific and Atlantic Oceans, has only one tide a day which is dirurnal.

While the tectonic plates are moving laterally and the seas are moving up and down, rivers flow from high areas to low areas, topographically speaking. A few rivers flow east to west or vice versa, depending upon which side of the continental divide they are on. Where eastern California meets western Nevada, there is a high spot. Water on the west side flows southwesterly down the American River of California to Sacramento and into the Sacramento River, which runs to San Francisco Bay and out under the Golden Gate Bridge into the Pacific Ocean. Water on the east side of the tippy-top of the Sierra Nevadas flows northeasterly down the Truckee River in Nevada.

Some continental divides are east-west, i.e., on either side of a north-south trending mountain range. Others, however, are north-south. Thus the Red River, or Riviere Rouge du Nord, originating in Minnesota, runs north via North Dakota to Lake Winnipeg in Canada, while a little to the east, the Mississippi runs south to the Gulf of Mexico. In Europe, the Volga River runs south to the Caspian Sea, while on the other side of the divide, the Elbe River runs northeasterly, ultimately dumping into the North Sea.

North-south rivers tend to be deflected to the west by a phenomenon known as the Coriolis effect after the physicist Gustave-Gaspard Coriolis, who discovered and described it.

Imagine that you own a big piece of land in the Midwest and you also own a big lake that sits on that land. You want to drain the lake so you can farm the fertile bottom. You dig a trench to a down-sloping area to the south of the lake’s edge and the water starts running out south. As it runs south, the Earth is turning easterly so that with each passing hour the new stream is moving slightly westerly. The water starts out south, but the Earth moving east under it deflects it to the west.

Coriolis force is also responsible for the westward migration of inlets to the ocean along Long Island’s south coast. As the water moves south from Great South Bay through the barrier island, for example, the water moves slightly to the west relative to the lay of the land, which is moving under it to the east. 

The inlet-outlet to Mattituck Creek in Southold Town on the North Fork has been moving to the west under the influence of the Coriolis effect. Its entrance was stabilized in the 1930s by jetties, so its inlet-outlet is now fixed in space well into the future. Shinnecock’s inlet is also jettied on both sides and so cannot migrate westerly as it started to do after opening in the 1938 hurricane.

Then there is the water beneath our feet, the water in the aquifers piled one atop the other, that provides all of our drinking water in Suffolk and Nassau Counties. If you were standing on the line dividing Southampton Town from East Hampton Town halfway to Sag Harbor, halfway to the ocean, and you had eyes like Superman, you could see the top of the topmost freshwater aquifer, the Magothy, about 30 feet above sea level in wet years, 20-plus during prolonged drought. This mound of water is not static. From its highest point it moves south to the ocean, north to the bay at the rate of about one foot a day. In other words, a drop just beginning to ooze south from the highest point today will take more than a thousand days to reach the ocean three miles away.

Groundwater, like all matter on Earth and under its surface, is pulled by two sets of gravitational forces. The Earth’s own pull toward its center, and the combined pull of the moon and the sun. When the moon is full, groundwater under that full moon is pulled slightly but measurably up. 

I remember standing barefoot in one of the mosquito ditches in Accabonac Harbor one summer day when the tide was just starting to rise from a moon-tide low. I was astonished when I felt the colder groundwater around my feet and looked down to see it bubbling up. Estuaries are tidal but have freshwater inputs, both from the surface of the land and from under it. Accabonac Harbor, itself a contributing water body to the Peconic Estuary, was acting as its own microestuary at that very moment.

All of this motion, up and down, back and forth, rapidly easterly, very, very slowly westerly, is making me dizzy. I think I’ll go to bed and conjure up a static dream to repair my equilibrium.


Larry Penny can be reached via email at