Shield volcanoes can grow to be very big. In fact, the oldest continentalregions of Earth may be the remains of ancient shield volcanoes.
Unlike the composite volcanoes which are tall and thin, shield volcanoes are tall and broad, with flat, rounded shapes. The Hawaiian volcanoes(see this) exemplify the common type of shield volcano. They are built by countless outpourings of lava that advance great distances from a central summit vent or group of vents. The outpourings of lava are typically not accompanied by pyroclastic material, which make the shield volcanoes relatively safe, as shown in this picture of scientists monitoring the eruption.
Mauna Loa, the largest of the shield volcanoes, is 13,677 feet above sea level, which means it rises over 28,000 feet above the deep ocean floor, and would be the worlds tallest mountain if much of it were not underwater.
source : pacificislandtravel.com, windows to the universe,