Geology of Island of Maui Island of Maui

Geology of Island of Maui • Island of Maui formed of two large shield volcanoes: –West Maui Shield Volcano, ~ age 1. 97 to 0. 39 Ma, Extinct Volcano • has rocks from all three sub aerial eruptive phases: shield, postshield alkalic cap, and rejuvenation –East Maui Shield Volcano, 1. 1 Ma to present, Active Volcano • has rocks from the late shield (rare) and postshield alkalic cap (most of the volcano’s modern surface) • is still in the postsheild alkalic cap stage • includes Haleakala crater - an erosional feature modified by later eruptions, Last erupted in 1790.

• Maui Nui -‘Greater Maui’ was geologically a very large island, now spilt into four smaller islands. • The four islands of Maui, Molokai Mo Mauiloka‘i, Lana‘i, and Kaho‘olawe formed a single landmass in the past called Maui Nui (Greater Maui) formed of 6 or 7 shield volcanoes. It included Penguin Bank, now a submerged shelf between Molokai and Oahu. • Around 2 million years ago, volcanoes on all of these islands as well as the Ko‘olau on O‘ahu were in their shield building stage, which means there were 7 to 9 active shield volcanoes at the same time.

About 300, 000 to 400, 000 years ago, Maui Nui, which grew from west to east. The Maui Nui subsided to form two islands, one consisting of Penguin Bank, Moloka'i, and Lanai, and the other consisting of Maui and Kaho'olawe then separated from Maui, and finally Lanai separated from Moloka'i, both within the last 100, 000 to 200, 000 years. Penguin Bank probably submerged within the last several hundred thousand years. During the last glacial maximum (LGM), about 21, 000 years ago, the Hawaiian Islands of Maui, Lanai, and Molokai were interconnected by limestone bridges, creating a super-island known as Maui-Nui. Approximately 120 m of sea-level rise during the Holocene Transgression flooded, and then drowned, these bridges separating the islands by inter-island channels. With continued subsidence at the present-day rates, East Maui (Haleakala) and West Maui will become separate

Hawaiian Islands Oahu Molokai k n a P B n i u eng Maui Lanai Kaho‘olawe Hawaii

Oahu Hawaii

Splitting act of the Island of Maui Nui

Molokai Maui n i u g Pen Bank Lanai Kaho‘olawe

Maui Nui probably had a maximum size of about 11, 000 square km (6, 200 square miles), some 4, 000 square km (2, 150 square miles) larger than present-day Hawaii.

West Maui Volcano and Caldera East Maui Volcano Haleakalā Rift Zones

West Maui volcano, in Rift Zones the lower left, is 1800 meters high (5900 feet) and is considered extinct. East Maui volcano, rises to an elevation of 3200 meters (10, 500 feet).

Shield

East Maui Shield Volcano Facts Location Lat 20. 7180 North Long 156. 2540 West Elevation Above Sea Level 3, 055 m, 10, 023 ft Area 1, 470 km 2 , 570 Radial mi 2 Drainage (77% of Island of Maui) Volume 30, 000 km 3 7, 200 mi 3 - 97% of Haleakala Crater formed between 145, 000 volume is below sea and 120, 000 years ago. It is a large erosional valley at the summit of East Maui Volcano. level Last erupted 1790 Island of Maui