GEOL 104 Lecture Notes - Lecture 9: Tephra, Lapilli, Pyroclastic Flow

• School: Queen's University
• Department: Geological Sciences and Geological Engineering
• Course: GEOL 104
• Professor: Daniel Layton- Matthews

Document Summary

Lecture 9: igneous rocks pt 4: volcanic rocks 2. Quiescent versus explosive eruptions: quiescent hawaiian type eruptions involves fluid basaltic lavas. Eruptions are characterized by outpourings of lava that can last weeks, months, or even years. Erupt on surface basaltic flow downhill stays molten from beginning to end as it cools, forms. About 90% of lava is basaltic lava. About 1% of lava is rhyolitic lava less than 10% of lava is andesitic lava: aa and pahoehoe flows are composed of basaltic lava. Aa flows have surface of rough jagged blocks. Pahoehoe flows have smooth surfaces and resemble twisted braids of rope: block lavas: composed of andesitic and rhyolitic lava upper surface consists of massive, detached blocks. Large chunks of solid rock formed of movement of lava upward and outwards of vent. Felsic in composition: pillow lavas: composed of basaltic lavas extruded underwater flow is composed of tubelike structures stacked one atop the other.