The amphidromic point is at once cotidal with high and low waters, which is satisfied by " zero " tidal motion . ( The rare exception occurs when the tide encircles an island, as it does around New Zealand, Iceland and Madagascar . ) Tidal motion generally lessens moving away from continental coasts, so that crossing the cotidal lines are contours of constant " amplitude " ( half the distance between high and low water ) which decrease to zero at the amphidromic point.
12.
The amphidromic point is at once cotidal with high and low waters, which is satisfied by " zero " tidal motion . ( The rare exception occurs when the tide encircles an island, as it does around New Zealand, Iceland and Madagascar . ) Tidal motion generally lessens moving away from continental coasts, so that crossing the cotidal lines are contours of constant " amplitude " ( half the distance between high and low water ) which decrease to zero at the amphidromic point.
