Vicente Soler, a volcanologist with Spain's National Research Council, said by flowing into the sea the lava was less likely to cause damage on land.
Thousands have been evacuated from their homes since the volcano erupted on September 19 and the lava flow has destroyed more than 800 buildings, as well as banana plantations, roads and other infrastructure.
After meandering downhill to the coast for nearly 10 days, the lava reached the ocean just before midnight on Tuesday (September 28) near the town of Tazacorte. On reaching the water, the lava cools rapidly, binding to the cliffside and enlarging the island's territory.
Despite fears of toxic gases from the lava reacting with the seawater, authorities said the air remained fine to breathe inland.