The Xenolith FlowThese barren rocks have sat on this site since 1802, when they arrived here after p
The Xenolith FlowThese barren rocks have sat on this site since 1802, when they arrived here after pouring out of Hualalai, one of the volcanoes that compose the main island of Hawaii.The Big Island of Hawaii is made of 5 volcanoes that today sit above the Pacific Ocean; Mauna Loa and Kilauea are the most active, Mauna Kea and Kohala are older and less active or extinct, and Hualalai is in the middle, between those groups.Hawaiian volcanoes are most active as they’re growing; once they get to about the size of Mauna Loa they slow down and erupt less. Mauna Loa right now erupts once every decade or few decades, Kilauea erupted non-stop for 3 and a half decades, and Hualalai erupts once every few centuries.This lava flow came out of Hualalai and made its way towards the North coast of the Big Island, destroying a few villages in the process. Today, the Kona airport actually is built on part of a lobe of this lava flow – you can see in the distance the difference in darkness between this younger flow and the older, weathered rock it covered.This flow is interesting from a geologic perspective since it is loaded with xenoliths – rocks that are picked up and carried by the flow as it goes. The xenoliths from this flow are made of dunites and gabbros and their presence tells us that there are dunites and gabbros deep within Hawaiian volcanoes.These rocks form as the volcanoes are growing: dunite is a rock rich in the mineral olivine, the first mineral to crystallize from Hawaiian lavas, while Gabbro is made of clinopyroxene and plagioclase, the next two abundant minerals that form from Hawaiian lavas. When the volcano is active and growing, it produces piles of dunite deep in its core when olivine grains form and sink, while the structure of the volcano gets built of rocks that look like gabbros. Late in the volcano’s life, its magma chamber cools off and solidifies, leaving behind a pile of dunite at its bottom with a pile of gabbro on top; the exact same rock chunks being ripped up and carried by this flow as it came through the once active cone.-JBBImage credit: Ken Lundhttps://flic.kr/p/7U4DoVRead morehttp://bit.ly/1GKWD1Thttp://bit.ly/1GMVIiohttp://bit.ly/1RR8lhA -- source link
Tumblr Blog : the-earth-story.com
#hualalai#volcano#xenolith#dunite#olivine#mineral#gabbro#igneous#volcanomonday#hawaii