GSCI 1051 Lecture Notes - Lecture 8: Extrusive Rock, Tephra, Tuff
Document Summary
Intrusions that blister upward are known as laccoliths they are fed by dikes. Radical dikes- arranged like spokes of a wheel. Ring dikes- arranged in concentric circles: round or irregular intrusions are plutons, extremely large ones are batholiths. Some crusts over increasing flow distance basalt flows form many different structures. Gas bubbles present when lava solidifies form vesicles. Columnar joints form as thick basalt flows cool. Pillows-blobs of lava that cool quickly under water: basalt flows aren"t explosive; they are effusive meanings they flow long distances. Intermediate lavas (andesite) are higher in silica, flow slowly, and cool quickly. Felsic lava (rhyolite) is the most viscous and rarely flows. Geology 1051: both highly explosive because of gas build up. Lava flows may come from cracks called fissures, causing fissure eruptions or lava comes from cylindrical pipes and forms volcanoes. Extrusive rocks- volcanic deposits volcanoclastic include broken rocks and ash: small fragments- la pilli, large fragments- bombs.
