Life Stages of Hawaiian Volcanoes

Why do Hawaiian Volcanoes Change With Time? Plate tectonics and hot spots –Source of magma is fixed in the mantle –Pacifc Plate is moving over magma source The types of volcanic activity are dependent on how close the volcano is to hot spot determining: –different magma types from varying degrees of partial melting –different frequencies of eruptions The ocean –different kinds of rocks form above, below, and at sea level –pronounced erosion above sea level

(Changed to “post-shield” stage)

When it first starts forming, not yet directly over hot spot so the volcano is first formed from alkalic basalt as the result of low degrees of partial melt When it first starts forming, not yet directly over hot spot so the volcano is first formed from alkalic basalt as the result of low degrees of partial melt As the submarine volcano moves over the hot spot, normal tholeiitic basalt starts to form from higher degrees of partial melt As the submarine volcano moves over the hot spot, normal tholeiitic basalt starts to form from higher degrees of partial melt Caldera and rift zone formation? Probably!! Yes!! Caldera and rift zone formation? Probably!! Yes!! Lava erupts as pillows with low vesicularity (few bubbles) due to high pressure in deep ocean environment Lava erupts as pillows with low vesicularity (few bubbles) due to high pressure in deep ocean environment Example: Lo‘ihi (“Long One”) Seamount Example: Lo‘ihi (“Long One”) Seamount

Lo‘ihi Seamount rift zone pit craters; (site of future caldera)

Tholeiitic basalt Tholeiitic basalt Characterized by hydromagmatic eruptions Characterized by hydromagmatic eruptions Submarine pyroclasts are called hyaloclastite Submarine pyroclasts are called hyaloclastite No volcano in Hawaii is currently in this stage No volcano in Hawaii is currently in this stage Evidence for this stage found by drilling through volcanoes, and by observing other volcanoes Evidence for this stage found by drilling through volcanoes, and by observing other volcanoes

Surtsey Island, Iceland

Tholeiitic basalt Tholeiitic basalt mostly “dry” pyroclasts mostly “dry” pyroclasts ‘a‘a and pahoehoe flows ‘a‘a and pahoehoe flows Well developed caldera and rift zones Well developed caldera and rift zones caldera indicates a shallow magma chamber caldera indicates a shallow magma chamber Bulk of volcano growth happens in this stage Bulk of volcano growth happens in this stage in geologic time, almost constant eruptions in geologic time, almost constant eruptions Examples: Kilauea and Mauna Loa Examples: Kilauea and Mauna Loa

Mauna Loa, a shield volcano

As volcano starts to move away from hot spot, magmas are again the result of low degrees of partial melt and are made of alkalic basalt As volcano starts to move away from hot spot, magmas are again the result of low degrees of partial melt and are made of alkalic basalt alkalic basalts have more volatiles, thus cause more explosive eruptions alkalic basalts have more volatiles, thus cause more explosive eruptions Later on, alkalic basalts evolve into more felsic--but still alkaline--rocks by crystal fractionation Later on, alkalic basalts evolve into more felsic--but still alkaline--rocks by crystal fractionation lower viscocity, thicker and shorter lava flows, and steeper slopes lower viscocity, thicker and shorter lava flows, and steeper slopes vents follow rift zones vents follow rift zones Eruptions less frequent, deeper magma chamber Eruptions less frequent, deeper magma chamber Examples: Mauna Kea, East Maui Volcano (Haleakala) Examples: Mauna Kea, East Maui Volcano (Haleakala)

Eruptions have ceased Eruptions have ceased Therefore, erosive processes now dominate as the action of wind and water wear the islands down to sea level Therefore, erosive processes now dominate as the action of wind and water wear the islands down to sea level Landslides also reduce the size of volcanoes Landslides also reduce the size of volcanoes Coral reefs grow on shallow submarine slopes Coral reefs grow on shallow submarine slopes Example: West Maui Volcano Example: West Maui Volcano

NaPali Coast, Kaua‘i

Moloka‘i

Also called Rejuvenation Stage Also called Rejuvenation Stage Magma produced by even lower degrees of partial melt than in the post-caldera alkalic cap - Nephalanites Magma produced by even lower degrees of partial melt than in the post-caldera alkalic cap - Nephalanites very low silica, very fluid lava very low silica, very fluid lava monogenitic eruptions--each vent erupts only once monogenitic eruptions--each vent erupts only once long periods of time can pass between each eruption long periods of time can pass between each eruption vents do not lie on the rift zones of the old shield vents do not lie on the rift zones of the old shield can have explosive hydromagmatic eruptions can have explosive hydromagmatic eruptions Example: on Ko‘olau Volcano, O‘ahu Example: on Ko‘olau Volcano, O‘ahu Diamond Head, Kaimuki, Koko Head, Tantalus, Punchbowl Diamond Head, Kaimuki, Koko Head, Tantalus, Punchbowl

Rejuvenation eruptions have mostly ceased Rejuvenation eruptions have mostly ceased Erosion has worn island down to sea level Erosion has worn island down to sea level Construction by coral reef growth only Construction by coral reef growth only Islands also sink due to: Islands also sink due to: Their own weight/Aging of the oceanic lithosphere Their own weight/Aging of the oceanic lithosphere Ultimately island becomes a guyot, a flat-topped seamount Ultimately island becomes a guyot, a flat-topped seamount Examples: Northwest Hawaiian Islands Examples: Northwest Hawaiian Islands Laysan, Midway, French Frigate Shoals, etc. Laysan, Midway, French Frigate Shoals, etc.

Laysan Island, an Atoll

Detailed Cross Section of a Hawaiian Shield Volcano km hyaloclastite

Hawaiian Swell Weight of the Hawaiian Islands bend the Pacific Plate Weight of the Hawaiian Islands bend the Pacific Plate The islands form the Hawaiian Ridge The islands form the Hawaiian Ridge At the islands, plate bends DOWN, forming the Hawaiian Deep or Moat At the islands, plate bends DOWN, forming the Hawaiian Deep or Moat But plate bends UP away from islands, forming the Hawaiian Arch But plate bends UP away from islands, forming the Hawaiian Arch

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