The landmass located roughly in the center of this image is the island of Hawaii, sometimes called the "Big Island". It is home to a highly active volcano, Mauna Loa -- "Long Mountain" in Hawaiian.
This shield volcano is the largest (5,271 square kilometers or 2,035 square miles in area) on the planet and one of its most active, erupting 33 times in recorded history. The Hawaiian Islands form part of an island arc, or a string of volcanoes that form above what geologists call a "hot spot".
As the Pacific plate (on which Hawaii currently rests) moved over a column of hot magma, the Hawaiian Islands were formed as the magma cooled into volcanic rock; how deep or shallow the column is remains an open and somewhat controversial research question.
The relative sizes of the islands give us insight into their ages and geologic history. The islands to the West are older and therefore smaller, having had more time to erode. The island of Hawaii is the youngest and therefore the largest in the chain. This image was acquired by the MODIS sensor aboard NASA's Terra Satellite on February 16, 2006.