Structure, stratigraphy, and eruption dynamics of a young tuff ring: Hanauma Bay, O’ahu, Hawai’i
Structure, stratigraphy, and eruption dynamics of a young tuff ring: Hanauma Bay, O’ahu, Hawai’i
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年轻凝灰岩环的结构、地层学和喷发动力学：夏威夷欧胡岛恐龙湾
DOI：
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发表时间：
2012
影响因子：
3.5
通讯作者：
B. Houghton
中科院分区：
文献类型：
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作者：
K. M. Rottas;B. Houghton
哈纳乌玛湾-科科岬复合体是位于奥克拉荷马州东南部的几个年轻的火山地貌之一，沿着科科裂缝。该复合体的Hanauma湾区域包括两个嵌套的凝灰岩环，内部和外部Hanauma湾，以及多个较小的喷口。内部凝灰岩环的内部结构，以及暴露由于随后的海洋和波浪侵蚀的突破，表明它形成在至少五个不同的沉积阶段，产生五个可映射的单位。显著的向内塌陷产生了主要的不整合面，这些不整合面将暴露在内壁中的单元分开。断裂面被狭窄的陡壁、局部悬垂的渠道和冲沟切割，这表明每次崩塌事件之后都有短时间的中断，在此期间，沉积物被降雨径流侵蚀。在每个火山碎屑岩单元内，都有许多局部滑塌疤痕和不整合面，这表明内壁的轻微不稳定性是一个几乎恒定的特征。从层理凹陷和浪涌床的形式，很明显，在凝灰岩环的生长过程中，通风口至少移动了两次。最年轻的单元中的弹道块表明，喷发与北部的单独喷发在时间上重叠，最有可能是880米外的Kahauloa凝灰岩环。
The Hanauma Bay–Koko Head complex is one of several young volcanic landforms along the Koko fissure, in southeastern O’ahu. The Hanauma Bay region of the complex comprises two nested tuff rings, inner and outer Hanauma Bay, and multiple smaller vents. The internal structure of the inner tuff ring, well exposed due to subsequent breaching by the ocean and wave erosion, indicates that it formed during a minimum of five distinct phases of deposition that produced five mappable units. Significant inward collapses generated major unconformities that separate the units exposed in the inner wall. The planes of failure are cut by narrow steep-walled, locally overhung channels and gullies, suggesting that the collapse events were each followed by short time breaks during which the deposits were eroded by rainfall runoff. Within each pyroclastic unit, there are many local slump scars and unconformities, suggesting that minor instability of the inner wall was a near-constant feature. From bedding sags and surge bed forms, it is apparent that the vent shifted at least twice during tuff ring growth. Ballistic blocks in the youngest unit indicate that the eruption overlapped in time with a separate eruption to the north, most likely to be that of the Kahauloa tuff ring 880 m away.