island of lana‘i formed of a single shield volcano, palawa caldera on the maui nui

•Island of Lana‘i •Formed of a single shield volcano, Palawa caldera on the Maui Nui•The Lana‘i volcano reached the subaerial sheild stage, has a single volcanic rock member

–Lana‘i Member, tholeiitic basalt, 1.46 to 0.78 Ma•pahoehoe and a‘ā, and and spatter cones on the rift zones

–caldera partly filled by lava, but is still visible–three rift zones

•grabens along rift zones

•This volcano also has has marine deposits, evidence for higher stands of the sea

Island of Lana‘i

Pacific Ocean

Lanai Volcano Palawa calderaRift zones

Pacific Ocean

Reef coral and basalt boulders deposits resting ~conformablyon basalt flows, ~100 m above sea level, south coast of Lana‘i-

Lanai slumped into sea on southwest: sea cliff exposing faults

Lāna‘i, volcanic ridge line is the old caldera rim

Island of Kaho‘olawe

Island of Kaho‘olawe• Formed of a single shield volcano

– Shield Stage, Lower Member (age unknown)• caldera is present but filled in, ~5 km diameter• typical shield lavas, tholeiitic basalt

– later shield-stage lavas have high silica (similar to Ko‘olau)» source rock for adzes found all over Hawai‘i

– Postshield Stage, Upper Member, ~1.0 Ma• small extent, include top part of caldera filling lavas• hawaiite

– Rejuvenation Stage Vents?• Youngest vents cut alluvium, but are tholeiitic (!); found at top of sea cliff

• Water problems--shallow wells yield brackish water– in rain shadow of Maui; also a low island– little vegetation--overgrazed (had been used as a ranch)– soil erosion by wind

• Eastern part of volcano is missing--landslide?– No debris, but eruptions from SW rift of East Maui may bury deposits

Kaholawee Volcano Caldera and rift zones

Pacific Ocean

Island of Kaho‘olawe

Pacific Ocean

Sea arches and sea cliffs exposing caldera-filling lavas