Cyclic eruptions and sector collapses at Monowai submarine volcano, Kermadec arc: 1998-2007
Cyclic eruptions and sector collapses at Monowai submarine volcano, Kermadec arc: 1998-2007
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DOI：
10.1029/2008gc002113
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发表时间：
2008-10-24
影响因子：
3.5
通讯作者：
de Ronde, C. E. J.
中科院分区：
文献类型：
--
作者：
Chadwick, W. W., Jr.;Wright, I. C.;de Ronde, C. E. J.
1998年、2004年和2007年，在Monowai Cone（一座浅海底玄武岩火山，也是Kermadec弧北方Monowai火山中心的一部分）进行了多次多波束测深勘测。这些调查记录了火山深度的巨大变化，包括两个部门坍塌造成的-176米的负变化和山顶附近火山重建造成的+138米的正变化以及滑痕下坡处的雪崩碎屑沉积物。1998年至2004年期间，一个扇区崩塌发生在东南斜坡上，体积类似于0.09 km（3），另一个扇区崩塌发生在2004年至2007年期间，西南斜坡上，体积类似于0.04 km（3）。由于火山爆发而增加的火山物质所引起的正深度变化量也是相同的数量级：1998年至2004年期间为0.05 km（3），2004年至2007年期间为0.06 km（3）。在这段时间内，波利尼西亚地震网的监测在Monowai发现频繁的T波群，表明每隔几个月就有爆炸性喷发活动。2002年5月24日的一个不寻常的T波群以前被解释为1998年和2004年调查之间的崩塌事件，但在2004年和2007年之间没有检测到类似的异常T波，可能是因为波利尼西亚地震台网的台站在第二次滑动事件中被声学遮蔽了。我们的解释是，Monowai上的扇区坍塌是由火山山顶和陡峭的上斜坡（> 20度）上的碎片喷发物质的不稳定负荷造成的。此外，似乎有一个周期性的模式，其中经常性的喷发过度陡峭的锥，并定期导致崩溃事件，运输火山喷发物质下坡到火山的较低的裙板。体积速率计算表明，这两个过程可能或多或少处于平衡状态。在Monowai的重复崩溃是相对温和的体积（仅涉及0.1-0.5%的建筑物体积），发生的频率比估计的更大的碎片雪崩在陆上火山，并可能是如何持续活跃的浅海底弧火山增长的特点。
Repeated multibeam bathymetric surveys at Monowai Cone, a shallow submarine basaltic volcano and part of the Monowai Volcanic Center in the northern Kermadec arc, were conducted in 1998, 2004, and 2007. These surveys document dramatic depth changes at the volcano including negative changes up to - 176 m from two sector collapses and positive changes up to + 138 m from volcanic reconstruction near the summit and debris avalanche deposits downslope of the slide scars. One sector collapse occurred on the SE slope between 1998 and 2004 with a volume of similar to 0.09 km(3), and another occurred on the SW slope between 2004 and 2007 with a volume of similar to 0.04 km(3). The volume of positive depth change due to addition of volcanic material by eruption is of the same order: similar to 0.05 km(3) between 1998 and 2004 and similar to 0.06 km(3) between 2004 and 2007. During these time intervals, monitoring by the Polynesian Seismic Network detected frequent T wave swarms at Monowai, indicative of explosive eruptive activity every few months. An unusual T wave swarm on 24 May 2002 was previously interpreted as the collapse event between the 1998 and 2004 surveys, but no similarly anomalous T waves were detected between 2004 and 2007, probably because the Polynesian Seismic Network stations were acoustically shadowed from the second slide event. We interpret that the sector collapses on Monowai are caused by the unstable loading of fragmental erupted material on the summit and steep upper slopes of the volcano (> 20 degrees). Moreover, there appears to be a cyclic pattern in which recurrent eruptions oversteepen the cone and periodically lead to collapse events that transport volcaniclastic material downslope to the lower apron of the volcano. Volumetric rate calculations suggest that these two processes may be more or less in equilibrium. The repeated collapses at Monowai are relatively modest in volume (involving only 0.1-0.5% of the edifice volume), have occurred much more frequently than is estimated for larger debris avalanches at subaerial volcanoes, and may be characteristic of how persistently active shallow submarine arc volcanoes grow.