Eruption and Emplacement Mechanisms and Paleoenvironment of Phreatomagmatic Tephra at Koko Crater Tuff Cone, O’ahu, Hawaii

摘要: The emplacement processes of proximal tuff cone deposits are often difficult to distinguish. This thesis focuses on the steep outer flank and surrounding apron Koko Crater, O’ahu, Hawaii. Four sections were logged in detail interpreted. slope dominated by slumped pyroclastic fallout deposits, some which may be directly eruption-fed, minor density current (PDC) that rarely slumped. lack slumping PDC is interpreted as due their lower eruption volumes, depositional rates, water content, longer transport distances, all favor more stable slopes. Slumping also less common previously substrate, slumps typically generate a gradient than primary deposits. occurrence overlying suggest generated column collapse (partial, sustained or complete). flanking i.e. those around base slopes, current, with rare probably because substrate gradients. increasing abundance distance from vent most likely compared ballistic fallout.