ABSTRACT

Overseas, relict deep-seated coastal landslides have attracted significant analysis because of potential hazards caused by sea level rise and climate change. Despite the rapid growth in the Auckland region, regional coastal landslide hazards are poorly understood. We investigated the geomorphology and material properties of Ohuka coastal landslide on the southwestern coastline of the Auckland region, to better understand the failure mechanism. The site is formed on weak Neogene sediments of varying lithological properties, with very low angles of dip, exposed on both the seaward (west) and landward (east) flanks of Ohuka Hill. Displacement appears to have been rotational, along a low-angled basal shear surface, the Koheroa Clay Seam. The surface geomorphology consists of discontinuous uphill-facing scarplets indictive of rotational slump blocks, along the basal shear surface. However, the preservation of slump block surface topography is hindered due to the lack of a thick, strong caprock, and high annual rainfall (1400 mm), and erosion. The proposed failure mechanism and general geometry is consistent with correlations between graben width and depth to failure plane reported from bedding-controlled coastal landslides formed on low dip angles in southern England. This provides important context, given the paucity of New Zealand bedding-controlled coastal landslide case studies.

摘要

在海外，由于海平面上升和气候变化造成的潜在危害，残留的深海海岸滑坡引起了重要的分析。尽管奥克兰地区发展迅速，但人们对区域沿海滑坡灾害知之甚少。我们调查了奥克兰地区西南海岸线 Ohuka 海岸滑坡的地貌和材料特性，以更好地了解破坏机制。该遗址形成于具有不同岩性特性的较弱的新近纪沉积物上，倾角非常低，暴露在 Ohuka 山的向海（西部）和向陆（东部）两侧。位移似乎是旋转的，沿着低角度的基底剪切面，即 Koheroa 粘土层。地表地貌由不连续的上坡深红色组成，表明旋转坍落块，沿基面剪切面。然而，由于缺乏厚而坚固的盖层和高年降雨量（1400 毫米）和侵蚀，坍塌块表面地形的保存受到阻碍。所提出的破坏机制和一般几何形状与地堑宽度和深度之间的相关性与英格兰南部低倾角形成的层理控制沿海滑坡报告的破坏平面的相关性一致。这提供了重要的背景，因为新西兰缺乏受控的海岸滑坡案例研究。所提出的破坏机制和一般几何形状与地堑宽度和深度之间的相关性与英格兰南部低倾角形成的层理控制沿海滑坡报告的破坏平面的相关性一致。这提供了重要的背景，因为新西兰缺乏受控的海岸滑坡案例研究。所提出的破坏机制和一般几何形状与地堑宽度和深度之间的相关性与英格兰南部低倾角形成的层理控制沿海滑坡报告的破坏平面的相关性一致。这提供了重要的背景，因为新西兰缺乏受控的海岸滑坡案例研究。