Beachcombers experienced a semiannual treat last week when the sun, moon and Earth aligned to produce extremely low tides at Clallam County beaches.

The low tides also canceled ferry sailings between Port Townsend and Keystone on Tuesday, Wednesday and Thursday mornings and kept trucks and buses with low ground clearance and long overhangs off the Edmonds-Kingston route.

If you missed them, you’ll get another opportunity in six months – although it will require venturing out at night.

The low tides at the entrance to Sequim Bay ranged from minus 2.9 feet on Sunday, June 21, to minus 3.6 feet on Tuesday, June 23. Anything in the minus 3-foot range is considered extremely low.

"Just as in real estate, these remarkably low tides are about location, location, location," said WSU Beachwatchers coordinator David Freed with Washington State University Extension.

Last week’s tides were especially profound examples of what are known as "spring tides," Freed said.

The unusually low tides are caused when the gravity and centrifugal force from the sun is aligned with the equal but opposite gravity and centrifugal force from the moon, so they compound each other, he said.

The alignment creates a greater gravitational pull than normal on the Earth’s oceans, Freed said.

"There’s forces at work because bodies have mass and this is an equal and opposite reaction of centrifugal force," he said.

These extremely low tides occur during the summer and winter solstices – the longest and shortest days of the year – when the Earth’s axis is tipping toward the sun and away from it, Freed said.

"These extremely low tides also happen in the wintertime, too, but they happen at nighttime in the winter. So mark your calendar: You’ll see them again just before Christmas," Freed said.

Some people are eager for those wintertime low tides because not only do they expose habitat not normally seen, there are creatures that are even more rare than in the summer, he said.

Freed said anyone who goes beachcombing during extremely low tides should bring a buddy along and be careful.

"Several beaches, especially in the Sequim area, do have real muddy areas. Those tidelands that are not exposed very often tend to be softer and could provide an opportunity to get stuck," Freed said.

"So go out with a buddy and be aware of your surroundings and keep moving. I find that when I stop moving is when I start to sink," Freed said.

People also should be careful to avoid stepping on the sea urchins, mussels, star fish and sea anemones that can be exposed during these semiannual low tides, he said.

Reach Brian Gawley at bgawley@

sequimgazette.com.