Magma of partial melting of the mantle, komatiite and picrite are produced. Magma develops within the mantle or crust where the temperature and pressure conditions favor the molten state. After its formation, magma buoyantly rises toward the Earth's surface. As it migrates through the crust, magma may collect and reside in magma chambers (though recent work suggests that magma may be stored in trans-crustal crystal-rich mush zones rather than dominantly liquid magma chambers ). Magma can remain in a chamber until it cools and crystallizes forming igneous rock, it erupts as a volcano, or moves into another magma chamber.There are two
Hogg Rock Jefferson to Santiam Pass includes shield volcanoes, lava domes, and cinder cones. The high elevation of Matuyama-aged rocks east of Santiam Pass, coupled with exposure of Brunhes-aged rocks to the west, imply the presence of a northward-trending normal fault. Part of a mostly mafic chain of volcanoes between the Three Sisters and Mount Jefferson, Hogg Rock has magma with an intermediate composition. A tuya, Hogg Rock is also considered a small lava dome with the flat top typically observed for tuya volcanoes. Unlike most lava domes in the Cascades, which are made of dacite or rhyodacite, Hogg Rock is comprised