Shield volcanoes are the common product of hotspot volcanism but they can also be found along subduction-related volcanic arcs or all by themselves. Here are 4 of the volcanoes that comprise the big island of Hawai'i. The photo was taken from near the summit of East Maui volcano EM. These are the largest volcanoes on Earth. This is a vertical air photo of the summit caldera of Mauna Loa volcano North is to the left. One lasted 1, years, ending in about CE; the other lasted years, between about and CE.
Effusive lava flows were the norm until about 2, years ago when the Powers caldera formed—the precursor to the present-day summit caldera. The caldera collapsed to a depth of at least m ft , where magma and external water interacted to trigger powerful phreatomagmatic water plus magma eruptions. Numerous explosive eruptions lasted for a period of about 1, years, producing the Uwekahuna tephra. Golf ball-sized rocks fell at the coast, 18 km 11 mi away.
The lava stream is about 3 m 10 ft wide. Lava flows finally began to erupt again about 1, years ago, breaking the 1,year-long interval dominated by explosive eruptions. Lava completely filled the summit caldera, then overflowed to form a new shield—the Observatory shield—in place of the caldera.
Flows spilled into the surrounding forest, which had grown during the previous centuries, and lava also erupted frequently along the volcano's east and southwest rift zones. Some archaeologists think people first arrived on the island in the beginning half of the 13th century, to years after the Observatory shield started to form.
Construction of the shield ended around the year CE. The caldera floor dropped to a depth of about m ft , with diameters of 3. This oral tradition describes the caldera's formation by a dramatic collapse of the volcano's summit area. Eruptions are also common in central vents near the summit of shield volcanoes, and along fissures radiating outward from the summit area.
Lava advances downslope away from their source vents in lava channels and lava tubes. Fissure eruptions are common occurrences on the "Big Island" of Hawaii.
They often begin as a line of vents curatin of fire that gives way to eruptions concentrated at one or two cental vents lying along the fissure.
The Pu'u O'o eruptive series , for example, has been erupting basaltic lava on the Kilauea shield volcano since These eruptions began on January 3 with a six-kilometer-long curtain of fire on the east rift system of Kilauea.
Intermittent fissure eruptions soon gave way to a centralized eruption site on the east rift, about 15 km east of the Kilauea summit caldera, which generated a scoria-and-spatter cone, called the Pu'u O'o volcano.
In the Kupaianaha volcano developed about 3 kilometers farther down rift. It erupted smoothed-surface pahoehoe lava until early Since that time the main eruption site has been centered at Pu'u O'o.
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