{"id":42690,"date":"2023-01-24T07:39:06","date_gmt":"2023-01-24T07:39:06","guid":{"rendered":"https:\/\/blogs.agu.org\/landslideblog\/?p=42690"},"modified":"2023-01-24T07:39:06","modified_gmt":"2023-01-24T07:39:06","slug":"blacks-beach-1","status":"publish","type":"post","link":"https:\/\/blogs.agu.org\/landslideblog\/2023\/01\/24\/blacks-beach-1\/","title":{"rendered":"A coastal cliff collapse at Blacks Beach, San Diego, California"},"content":{"rendered":"<h4>A coastal cliff collapse at Blacks Beach, San Diego, California<\/h4>\n<p>On 20 January 2023 a large section of coastal cliff failed at Blacks Beach in San Diego, <a href=\"https:\/\/blogs.agu.org\/landslideblog\/?s=california&amp;submit.x=41&amp;submit.y=15&amp;mswhere=blog\">California<\/a>.\u00a0 <a href=\"https:\/\/www.youtube.com\/watch?v=5RV9b6ZQBSw\">The landslide was captured on a video that has been posted to Youtube by Kent Ameyaro<\/a>.\u00a0 It is well worth viewing:-<\/p>\n<iframe loading=\"lazy\" title=\"Blacks Beach San Diego Bluffs Collapse (1:29pm Jan 20 2023)\" width=\"800\" height=\"450\" src=\"https:\/\/www.youtube.com\/embed\/5RV9b6ZQBSw?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" allowfullscreen><\/iframe>\n<p>.<\/p>\n<p><a href=\"https:\/\/www.youtube.com\/watch?v=M-X2-FN9pb0\">There is another video of a part of the landslide on the KTVB Youtube channel<\/a>:-<\/p>\n<iframe loading=\"lazy\" title=\"Cliff collapses above San Diego County beach\" width=\"800\" height=\"450\" src=\"https:\/\/www.youtube.com\/embed\/M-X2-FN9pb0?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" allowfullscreen><\/iframe>\n<p>.<\/p>\n<p><a href=\"https:\/\/www.youtube.com\/watch?v=tblSl11fdaA\">And there is a nice view of the aftermath of the failure on the CBS 8 San Diego Youtube channel<\/a>:-<\/p>\n<iframe loading=\"lazy\" title=\"Bluff Collapses at Black&#039;s Beach in La Jolla\" width=\"800\" height=\"450\" src=\"https:\/\/www.youtube.com\/embed\/tblSl11fdaA?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" allowfullscreen><\/iframe>\n<p>.<\/p>\n<p>The landslide at Blacks Beach is located at 32.885, -117.253.\u00a0 I&#8217;ve found a <a href=\"https:\/\/gotbooks.miracosta.edu\/fieldtrips\/torrey_pines\/index.html\">nice description of the geology of this area<\/a>,<a href=\"https:\/\/gotbooks.miracosta.edu\/fieldtrips\/torrey_pines\/images\/egc5_geology.jpg\"> including this image of the sedimentary sequence at Black Beach<\/a>.\u00a0 \u00a0 The Ardath Shale is described as:<\/p>\n<p><em>&#8220;&#8230;a mix of shale, silty shale, with some beds of sandstone and conglomerate that are similar in physical appearance to some beds in the other Eocene-age rock formations. However, the Ardath Shale is dominated by steep-slope-forming shale (not the nearly vertical cliffs of the sandstone and conglomerate beds). The soft shale beds erode easier forming alcoves beneath waterfalls and is susceptible of forming slumps.&#8221;<\/em><\/p>\n<p>The landslide itself is complex.\u00a0 The principal mechanism of failure is a deep-seated rotational failure, which goes through its main (most rapid) movement phase from about 3:00 for about 45 seconds.\u00a0 During this time the uplift of a shale bed at the toe develops beautifully, and the slumping at the crown of the landslide is also clear (and is evidenced by the exposure of less weathered material at the base of the cliff at the top of the slump block in the image below):-<\/p>\n<div id=\"attachment_42693\" style=\"width: 809px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-42693\" class=\" wp-image-42693\" src=\"https:\/\/blogs.agu.org\/landslideblog\/files\/2023\/01\/22_01-Blacks-Beach-1.jpg\" alt=\"The 20 January 2022 landslide at Blacks Beach in California. \" width=\"799\" height=\"383\" srcset=\"https:\/\/blogs.agu.org\/landslideblog\/files\/2023\/01\/22_01-Blacks-Beach-1.jpg 1271w, https:\/\/blogs.agu.org\/landslideblog\/files\/2023\/01\/22_01-Blacks-Beach-1-300x144.jpg 300w, https:\/\/blogs.agu.org\/landslideblog\/files\/2023\/01\/22_01-Blacks-Beach-1-1024x491.jpg 1024w, https:\/\/blogs.agu.org\/landslideblog\/files\/2023\/01\/22_01-Blacks-Beach-1-768x368.jpg 768w\" sizes=\"auto, (max-width: 799px) 100vw, 799px\" \/><p id=\"caption-attachment-42693\" class=\"wp-caption-text\"><em>The 20 January 2022 landslide at Blacks Beach in California. <a href=\"https:\/\/www.youtube.com\/watch?v=5RV9b6ZQBSw\">Still from a video posted to Youtube<\/a>.<\/em><\/p><\/div>\n<p>.<\/p>\n<p>In the three minutes leading up to this point multiple smaller failures and collapses can be seen.\u00a0 This is probably an indication that movement was occurring on the rotational shear surface, causing extensive internal deformation to the slump block, driving these smaller failures.<\/p>\n<p>After the main phase of movement the landslide became more stable, but smaller collapses continued to occur.\u00a0 This is common in such circumstances.<\/p>\n<p>Whilst the landslide occurred on a sunny day, <a href=\"https:\/\/blogs.agu.org\/landslideblog\/2023\/01\/16\/california-1\/\">California has endured a succession of atmospheric river events<\/a> that have been associated with heavy rainfall and large waves.\u00a0 Thus, the landslide might be the result of higher than normal pore water pressures and\/or toe erosion.<\/p>\n<p>.<\/p>\n<h4>Acknowledgement<\/h4>\n<p>Many thanks to loyal reader Jonas Van Rutte for highlighting this landslide to me.<\/p>\n<!-- AddThis Advanced Settings generic via filter on the_content --><!-- AddThis Share Buttons generic via filter on the_content -->","protected":false},"excerpt":{"rendered":"<p>On 20 January 2023 a large coastal cliff collapse at Blacks Beach, San Diego, California was captured on a truly amazing video.<!-- AddThis Advanced Settings generic via filter on wp_trim_excerpt --><!-- AddThis Share Buttons generic via filter on wp_trim_excerpt --><\/p>\n","protected":false},"author":22,"featured_media":42693,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":"","_members_access_role":[],"_members_access_error":""},"categories":[29],"tags":[137,732,469,963,725,151,48],"class_list":["post-42690","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-landslide-video","tag-california","tag-coastal-cliff","tag-featured","tag-landslide-video","tag-north-america","tag-rotational-landslide","tag-usa"],"_links":{"self":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/42690","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/users\/22"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/comments?post=42690"}],"version-history":[{"count":0,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/42690\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/media\/42693"}],"wp:attachment":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/media?parent=42690"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/categories?post=42690"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/tags?post=42690"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}