CHAPTER 1 THE CHANGING TIDE Muddy sand stretches to the ocean The sunny beach seems peaceful But there’s a battle taking place It’s a struggle between land and sea For now the water appears to be winning It moves up the shore swallowing more and more of the beach Finally the beach is completely covered by water The tide moves up toward the rocks on the coast of California 5
But this fight isn’t over At just past the six-hour mark the water holds still Then the ocean begins to pull away It loses ground to the land A little more than 12 hours after it began its advance the water has gone into full retreat It no longer covers the beach The exposed mud dries in the cooling night Then the process starts all over The water begins creeping back up the shore This regular rise and fall of the ocean surface is known as the tide As the water level rises and falls it creates currents in the water A flood current moves inland with a rising tide It washes up over the shoreline Over the next few hours the 6
A flood current rushes in at Porthminster Beach in Cornwall England tide falls The water moves back out This is an ebb current Most coastal areas have two high tides and two low tides each day The water rises to high tide in slightly more than six hours Then it falls back to low tide 7
