"It is not a river": Lava can disperse in other directions even though it now flows into the sea.“No es un río”: La lava puede dispersarse en otras direcciones aunque ahora fluya hacia al mar. (El Pais.es )

The arrival of the wash in the ocean does not guarantee that it will only follow that channel from now on. The natural thing is that it falls down the same slope, but it could take other paths after cooling down or covering the topography