Under the Hawaiian Islands, there is a volcanic “hot spot,” a hole in the Earth’s crust that allows lava to surface and layer. Over millions of years, these layers form mountains of volcanic rock that eventually break the surface of the Pacific Ocean, forming islands. As the Pacific Plate very slowly moves across the hot spot, new islands are formed. It took 80 million years to create the current chain of Hawaiian islands.
Discovering the Hot Spot
In 1963, John Tuzo Wilson, a Canadian geophysicist, introduced a contentious theory. He hypothesized there was a hot spot under the Hawaiian Islands - a mantle plume of concentrated geothermal heat that melted rock and rose up as magma through fractures under the Earth’s crust.
At the time they were introduced, Wilson’s ideas were very controversial and many dubious geologists were not accepting theories of plate tectonics or hot spots. Some researchers thought that volcanic areas were only in the middle of plates and not at subduction zones.
However, Dr. Wilson’s hot spot hypothesis helped to solidify the plate tectonics argument. He provided evidence that the Pacific Plate has been slowly drifting over a deep-seated hot spot for 70 million years, leaving behind the Hawaiian Ridge-Emperor Seamount Chain of more than 80 extinct, dormant, and active volcanoes.
Wilson worked diligently to find evidence and tested volcanic rock samples from each volcanic island in the Hawaiian Islands.
He found that the oldest weathered and eroded rocks on a geological time scale were on Kauai, the northernmost island, and that rocks on the islands were gradually younger as he went south. The youngest rocks were on the southernmost Big Island of Hawaii, which is actively erupting today.
The ages of the Hawaiian Islands gradually decrease as seen in the list below:
- Niihau and Kauai (5.6 - 3.8 million years old).
- Oahu (3.4 - 2.2 million years old)
- Molokai (1.8 - 1.3 million years old)
- Maui (1.3 - 0.8 years old)
- Big Island of Hawaii (less than 0.7 million years old) and it is still expanding.
The Pacific Plate Conveys the Hawaiian Islands
Wilson’s research proved that the Pacific Plate has been moving and carrying the Hawaiian Islands northwest off the hot spot. It moves at a rate of four inches a year. The volcanoes are conveyed away from the stationary hot spot; thus, as they move farther away they become older and more eroded and their elevation decreases.
Interestingly, about 47 million years ago, the path of the Pacific Plate changed direction from north to northwest. The reason for this is unknown, but it might have been because of India colliding with Asia at approximately the same time.
The Hawaiian Ridge-Emperor Seamount Chain
Geologists now know the ages of the undersea volcanoes of the Pacific. In the farthest northwest reaches of the chain, the underwater Emperor Seamounts (extinct volcanoes) are between 35-85 million years old and they are highly eroded.
These submersed volcanoes, peaks, and islands extend 3,728 miles (6,000 kilometers) from the Loihi Seamount near the Big Island of Hawaii, all the way to the Aleutian Ridge in the northwest Pacific. The oldest seamount, Meiji, is 75-80 million years old, whereas the Hawaiian Islands are the youngest volcanoes - and a very small part of this vast chain.
Right Under the Hot-Spot: Hawaii’s Big Island Volcanoes
At this very moment, the Pacific Plate is moving over a localized source of heat energy, namely, the stationary hot spot, so active calderas continually flow and erupt periodically on the Big Island of Hawaii. The Big Island has five volcanoes that are connected together – Kohala, Mauna Kea, Hualalai, Mauna Loa, and Kilauea.
The northwestern part of the Big Island ceased erupting 120,000 years ago, whereas Mauna Kea, the volcano in the southwest part of the Big Island erupted only 4,000 years ago. Hualalai had its last eruption in 1801. Land is continually being added to the Big Island of Hawai’i because lava that flows from its shield volcanoes is deposited on the surface.
Mauna Loa, the largest volcano on Earth, is the most massive mountain in the world because it occupies an area of 19,000 cubic miles (79,195.5 cubic km). It rises 56,000 feet (17,069 m), which is 27,000 feet (8,229.6 km) higher than Mount Everest. It is also one of the world’s most active volcanoes having erupted 15 times since 1900. Its most recent eruptions were in 1975 (for one day) and in 1984 (for three weeks). It could erupt again at any time.
Since Europeans arrived, Kilauea has erupted 62 times and after it erupted in 1983 it stayed active. It is the Big Island’s youngest volcano, in the shield forming stage, and it erupts from its large caldera (bowl-shaped depression) or from its rift zones (gaps or fissures).
Magma from the Earth’s mantle rises to a reservoir about one-half to three miles under Kilauea’s summit, and pressure builds up in the magma reservoir. Kilauea releases sulfur dioxide from vents and craters - and lava flows onto the island and into the sea.
South of Hawaii, about 21.8 mi (35 km) off the coast of the Big Island, the youngest submarine volcano, Loihi, is rising from the sea floor. It last erupted in 1996, which is very recent in geological history. It is actively venting hydrothermal fluids from its summit and rift zones.
Rising up about 10,000 feet above the ocean floor to within 3,000 feet of the water surface, Loihi is in the submarine, pre-shield stage. In accordance with the hot spot theory, if it continues to grow, it might be the next Hawaiian Island in the chain.
The Evolution of a Hawaiian Volcano
Wilson’s findings and theories have increased knowledge about the genesis and life cycle of hot spot volcanoes and plate tectonics. This has helped to guide contemporary scientists and future exploration.
It is now known, that the heat of the Hawaiian hot spot creates fluid molten rock that consists of liquefied rock, dissolved gas, crystals, and bubbles. It originates deep below the earth in the asthenosphere, which is viscous, semi-solid and pressurized with heat.
There are huge tectonic plates or slabs that glide over this plastic-like asthenosphere. Due to the geothermal hot spot energy, the magma or molten rock (which is not as dense as the surrounding rocks), rises through fractures from under the crust.
The magma rises and pushes its way through the tectonic plate of the lithosphere (the rigid, rocky, outer crust), and it erupts on the ocean floor to create a seamount or underwater volcanic mountain. The seamount or volcano erupts under the sea for hundreds of thousands of years and then the volcano rises above the sea level.
A large amount of lava is added to the pile, making a volcanic cone that eventually sticks out above the floor of the ocean - and a new island is created.
The volcano keeps growing until the Pacific Plate carries it away from the hot spot. Then the volcanic eruptions cease to erupt because there is no longer a lava supply.
The extinct volcano then erodes to become an island atoll and then a coral atoll (ring shaped reef). As it continues to sink and erode, it becomes a seamount or guyot, a flat underwater tablemount, no longer seen above the water’s surface.
Overall, John Tuzo Wilson provided some concrete evidence and deeper insight into the geological processes above and below the surface of the Earth. His hot spot theory, derived from studies of the Hawaiian Islands, is now accepted, and it helps people understand some ever-changing elements of volcanism and plate tectonics.
Hawaii’s undersea hot spot is the impetus for dynamic eruptions, leaving behind rocky remnants that continually enlarge the island chain. While older seamounts are declining, younger volcanoes are erupting, and new stretches of lava land is forming.
Updated on : Aug 22, 2016 View : 1049