Skip to page body Home About Us What's New City Government Departments Living Visiting Doing Business I Want To...

Point 9 - Stage Commons # 2, Kelp Forest Surfing, Waves

Move your mouse over the numbers on the map for a brief description and click to go there.

Point 9
Tides & Waves
As you watch the sea touch the land here, two things are always working: waves and tides. We touched on this subject a couple of kiosks back, but the grind effect is more apparent from this spot. Both transport sediment along the coast and make what we call beaches. They erode the coastal bluffs away and you can see places where caves have been hollowed out.

The greatest throw of tides on west coast can make 10-15 feet change in water depth. We commonly can see changes of six feet or so. You can see the vertical tide water marks on the wharf pilings. The greatest throw of tide is Puget Sound and Cook Inlet, Alaska, which is 15-20 feet.

As we said earlier, there are usually four tide switches a day, two high tides of different heights and two low tides of unequal height. This is different than the east coast, where the tides are equal in height all day and night.

Tides are the result of the gravitational pull of the moon and the sun. When they are lined up with the earth in a straight line, a new moon and a full moon, the tides are most extreme. A high tide is very high and a low tide is very low. A popular name for this condition is "spring tides."

But during a half moon when the sun and moon are at right angles compared to the earth, those gravity forces cancel each other, and we get what we call "neap tides," which are not extreme.

Because the lunar month is different that the solar month, spring and neap tides follow each other every other week, or alternate weeks. And because the moon revolves around the earth, the tides happen a little later each day, meaning our tides occur at different times of the day during different seasons.

Waves are beautiful and strange things. Although they seem to be moving walls of water, actually "the wave" is one of energy traveling through the water and is not water traveling. Water particles, or a floating object in the water move very little; just up and down in a circular motion. The energy waves are generated far out to sea by storms and undersea earthquakes. The wave energy can travel very fast, even a hundred miles an hour.

In the deep ocean, the wave action seems like chaos; they travel in all directions at once; there are no lines of surf, just bouncing mounds that pop up and down and move one way then the opposite way. When energy waves approach the land onshore, they begin to run out of room on the bottom as they get closer to shore. The slope of the undersea pushes the wave upwards and we see swells and surf. There seems to be a ratio of height vs length before a wave breaks into white surf. It is a ratio of 1:7. As soon as the wave slope height exceeds 1/7th the length, it curls over and breaks into white water. The turbulent surf is very powerful and can wear down the land or the structures it hits.

Back to top

Kelp Forest
Over at the point you can see kelp beds. Kelp is another one of those living things that is radically different from anything on the land. It is a marine plant. It is an algae actually. It can boast about being the fastest growing plant on earth, or earth/sea: in summer, up to 18 inches a day.

There are two categories of marine plants: the algae's and marine grasses. The kelp algae is very different from land plants in that there are no roots to speak of, just "holdfasts" which anchor the kelp columns to the rocky reefs.

Scientists have estimated that the large kelps and marine grasses growing in a narrow belt on just 5% of the earths' surface produce over one third of the ocean's productivity. The two large kelp plants we see in the kelp forest are bull kelp and perennial kelp. After heavy surf or storms you can find a number of different kinds of kelps that are scoured up off the bottom and deposited on the beach. They are all textures and colors. Some are leafy, tough, soft, flat, tubular, branched or make of narrow filaments.

The large kelps are nourished by the sea around them and have not developed roots, stems, nor leaves. They produce no flowers, seeds, or fruits. They reproduce by a variety of single-celled and leafy forms, both asexual and sexual.

The kelp forests make for a rich biological home for many marine creatures, just as forests do on land. Young fishes grow in the protection of the kelp columns and a number of animals lay their eggs in the kelp fronds. The storms of winter will tear off the kelp canopy and dump tons of it on the beaches. Lots of shorebirds and benthic organisms find food in the kelp detritus.

Turning around the other way, we can see the new Marine Sanctuary Office upstairs. Let's take a walk up there. They can tell you more about the Marine Sanctuary and you get the best view on the Wharf.

Previous Point  Point 1 2 3 4 5 6 7 8 9 10 11 12 13  Next Point

Last updated: 1/12/2010 2:07:54 PM