First, start a pillar up to an appropriate height a few blocks from the protected area. (tip: if by deep ocean, use a lilypad to start.) (hint #2: start the next phase just below the base.
Second, create a "cup" with the side nearest the target broken and fill the center with lava, wait for the lava to spread and is pouring vertically before dumping out with water
(hint place a block ontop of the source block and dump the water on the top block to preserve lava).
Third: Once you are either connected to the base or are capable of jumping, set foot on the base).
Fourth: Do as you wish...