If you anchor your eyes on the rock at the left of the two pictures above, you’ll be see how both photographs are related.
The beach visible on the second photograph is covered by the tide on the first.
If you want to go to the beach, to know whether the tide is high or low is important to make sure there is a beach when you arrive.
If, like Andrea, you can’t swim and want to be under the arch when the full moon rises so that you can cross to Earth, this knowledge is a matter of life and death.
This is what happens when she forgets to check:
Down below, the ocean had once more claimed the stretch of land that was the Cove of the Dead, and only the Arch, a naked rock, like an island dressed in foam, was still visible. From where I stood at the top of the cliffs, I could see the waves breaking against the mouth of the cave. I hesitated. The prospect of getting to the arch across the water was not a pleasant one, since I still could not swim. But waiting for the tide to recede was not an option. Lua would be rising any moment now, and I would lose my chance to cross if I did not make it to the cave soon.
My skirts tucked around my waist, I crawled over the boulder that blocked the trail. Turning my back to the ocean, I started down the crude steps carved into the wall. I climbed for what seemed forever until my feet touched the water. Shivering from both its frozen touch and my fear that I would never reach the sand in time, I kept on going, lowering hands and feet one at a time into the now slippery holes. Steadily the water rose, past my knees and up my hosiery.
I stopped then, afraid that my skirts, heavy with water, would drag me down. I was about to climb back when I realized my right foot was not on rock but on soft ground. Tentatively I lowered my left foot. Yes! It stayed level with the other: I had reached the bottom. Taking in a deep gulp of the moist salty air, I released my grasp of the wall and turned.
All I saw was water, dark green, angry water roaring toward me. I yelped as a wave broke against my chest, sending me backward, a hapless doll against the rocks.
From Two Moon Princess (http://goo.gl/VX0r1)