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10 May
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HP91 – Hawaiian Volcanoes

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Hawaiian VolcanoesHi my name is Michelle; I’m the wife of the History Podcast’s founder Jason. I have presented some episodes quite a while ago, so I thought I’d release an episode after an extended hiatus.

This podcast is on the History of the Hawaiian volcanoes. Here’s some insight as to why I selected this particular topic. I have always been intrigued and fascinated by volcanoes. I’m grateful for having the opportunity to view the dramatic differences in the size, scope, and topography of a few volcanic areas. I have visited Mount Lassen, a volcano in Northern California multiple times. Plus, I walked the calderas of Yellowstone National Park, a few years ago. These volcanic areas are definitely scenic, despite the foul odors caused by sulfur gases. The volcanic chain that makes up the Hawaiian Islands is so beautiful and vibrant. Seeing Diamond Head on the Island of Oahu and the volcanic rocks on Kauai, I decided to learn more about this volcanic chain that forms the Hawaiian Islands. The main Hawaiian Islands visited by tourists consist of: Kauai, Oahu, Maui, Molokai, Lanai, and Hawaii.

Here’s a brief discussion to the History of the Hawaiian Volcanoes:

The Hawaiian Volcanoes are a type of volcano called hotspots. In geology, a hotspot is a location on the Earth’s surface that has experienced active volcanism for a long duration of time. The hot and fluid type of magma creating these volcanic products is basalt. Hotspot volcanoes tend to be shield volcanoes that rarely erupt explosively and practically all are found on oceanic plates. The Hawaiian volcanoes are the most studied hotspot volcanoes and are situated in close proximity to the Pacific Plate. Most of the Hawaiian volcanoes, specifically the volcanoes that make up the Hawaiian Islands, go through several defined stages of evolution during their lifespan. These growth stages are impacted by the position of the volcano in relation to the hotspot, whether the volcano’s summit lies below, near, or above sea level, as well as by the composition of the lava being erupted.

As just shared, various stages of volcanic activity exist, with a majority of the volcano’s growth occurring in the shield stage. During this stage of growth, the volcano accumulates about 95 percent of its mass and it takes on the “shield” shape, hence the name shield volcanoes. In addition, this is the stage where the volcano’s eruptive frequency reaches its peak. The phases of the shield stage consist of: submarine, explosive, and subaerial phases. When volcanoes come close to sea level, the pressures that prevented explosive reactions between erupting lava and water no longer exist. As this point is reached, the volcanoes enter the explosive phase of the shield stage. In this phase, lava and seawater interact to cause explosive eruptions. These eruptions are rich in ash and continue intermittently for several hundred thousand years. Calderas continually develop and fill, and the rift zones remain prominent. The phase ends when the volcano has sufficient mass and height, typically about 4,000 feet above sea level. The constant interactions between seawater and erupting lava at vent locations no longer occur at the conclusion of the explosive phase. During Subaerial Phase, the explosive eruptions become much less frequent and the nature of the eruptions become much more subdued. The edges of the growing volcanoes are unstable causing potential landslide occurrences. This stage is arguably the most well-studied, due to all eruptions that occurred in the 20th century in Hawaii were produced by volcanoes in this phase. Mauna Loa and Kilauea volcanoes are in this phase of activity.

Kilauea and Mauna Loa are two of the most active volcanoes in the world, which are located on the island of Hawaii on the southeast end of the Hawaiian Volcanic chain. In addition, the five volcanoes that form the island of Hawaii are all less than 1,000,000 years old.

In the northwestern direction, the Hawaiian Islands are progressively older. The extinct volcano that formed the island of Kauai is about 5,000,000 years old. That means that there is a span of 4,000,000 years difference in volcanic age between the islands of Kauai and Hawaii. Evidence has suggested that the hotspot forming the Hawaiian volcanoes is in a relatively fixed position. As a result, the movement of the Pacific Plate has been northwestward at a rate of approximately 10 cm annually. The Emperor Seamounts encompass an entirely submarine ridge that continues northward to the edge of the Pacific Plate. By viewing topographic maps, the Hawaiian Islands are a continuation to the Hawaiian ridge and bend into the Emperor Seamounts.

The ages of the volcanic rocks of the Emperor Seamounts, garnered by dredging and drilling, has determined that the Hawaiian-Emperor Ridge is a progressively older volcano formed at by volcanism at the Hawaiian hot spot. This integral center of volcanism in the Pacific has been active for at least 80MM years. The Pacific Plate has moved over it as just mentioned at the rate of 8 – 10 cm per year. The bend that exists between the Emperor Seamount and Hawaiian Ridge occurred about 40MM years ago. This indicates a noteworthy shift in the direction of the Pacific Plate.

The rationale for a volcanic hotspot maintaining its position for millions of years with a plate passing over it is unknown. A theory is that a hotspot is a deep mantle plume caused by very slow convection of highly vicious mantle material. With hot yet solid material moving upward, partial melting may occur from the lowering of its pressure dependent melting temperature. Within the next couple of decades, due to thorough seismic sounding of the mantle, the knowledge of the mechanics of hotspots should be discovered and understood more fully.

Hope the concise background of the formation of the Hawaiian Volcanoes proved enlightening. In conclusion, I wanted to share that the United States National Parks Service includes the Hawai`i Volcanoes National Park. The park highlights two of the world’s most active volcanoes just mentioned, Kilauea and Mauna Loa. Extensive insight on the birth of the Hawaiian Islands and views of dramatic volcanic landscapes are offered at this National Park.

Here’s some relevant trivia:

The Hawaiian Islands form an archipelago of nineteen islands and atolls, numerous smaller islands and atolls, and undersea seamounts trending northwest by southeast in the North Pacific Ocean. The Hawaiian Islands were once known as the Sandwich Islands, which was the name given to the Hawaiian Islands by Captain James Cook on his discovery of the islands on January 18, 1778. The name was made in honor of one of his sponsors and superior officer, John Montague, 4th Earl of Sandwich. During the late 19th century, the name Sandwich Islands was no longer a term used to reference the Hawaiian Islands.

Mahalo or thank you in Hawaiian for listening to this history podcast!

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