The term 'SOURCE OF LAVA' can be answered with the 7-letter word 'VOLCANO'. Volcanoes are geological landforms created by the eruption of molten rock, known as lava, from a vent in the Earth's surface. This molten rock is formed deep within the Earth's mantle and is composed of magma, which is heated to extreme temperatures and pressure. When this magma reaches the Earth's surface, it is released in an explosive eruption, creating a VOLCANO.