tag:blogger.com,1999:blog-4706799725776420299.post5872064439372938021..comments2023-10-11T08:53:44.814-05:00Comments on Geology in Motion: The mysterious grooves on Barcena volcanoSusan W. Kiefferhttp://www.blogger.com/profile/13703399168416944593noreply@blogger.comBlogger3125tag:blogger.com,1999:blog-4706799725776420299.post-32542896971661925562019-01-21T16:52:20.054-06:002019-01-21T16:52:20.054-06:00Marc, I just returned from Hawaii where I saw good...Marc, I just returned from Hawaii where I saw good examples of parasol ribbing. It seemed quite different to me from the Barcena gullies, especially in their irregular cross-sections. It would be a good project to compare cross-sections along the stream wise direction for Barcena and the rain-eroded gullies, but sadly there just isn't enough photodocumentation of the fresh Barcena gullies to permit this.Susan W. Kiefferhttps://www.blogger.com/profile/13703399168416944593noreply@blogger.comtag:blogger.com,1999:blog-4706799725776420299.post-42149367104623177772018-04-14T19:50:42.616-05:002018-04-14T19:50:42.616-05:00Thank you very much for this information, Marc! I ...Thank you very much for this information, Marc! I will look up whether parasol ribbing can explain the regular spacing.Susan W. Kiefferhttps://www.blogger.com/profile/13703399168416944593noreply@blogger.comtag:blogger.com,1999:blog-4706799725776420299.post-9182284054461500112018-04-14T19:32:20.704-05:002018-04-14T19:32:20.704-05:00The Volcano Letter was published by HVO from 1925 ...The Volcano Letter was published by HVO from 1925 to 1955. There are a total of 530 issues. <br /><br />The issues dealing with Barcena/Boqueron Volcano (San Benedicto Island) are:<br />517 (page 7, Jul-Sep 1952) by Howel Williams<br />519 (page 7, Jan-Mar 1953) by Adrian Richards<br />520 (page 7, Apr-Jun 1953) by anon.<br />These are just 2-4 paragraphs each in the Volcano Notes and News section<br /><br />The only information relevant to your blog post is in issue 517: "...explosions that lifted the ejecta only a short distance above the crater rim so that they then swept down the outer flanks of the cone as glowing avalanches."<br /><br />These grooves look to me like rain eroded parasol ribbing. The absence of dendritic geomorphology is not surprising as the surface area expands downhill rather than reducing as in a dendritic stream network. The regular distribution of the grooves (at least in the part of the cone visible in the photograph) argues against an origin by PDC. Why would they be so evenly spaced?<br /><br />Cheers,<br />Marc Bernstein<br /> Anonymoushttps://www.blogger.com/profile/15404365997813305527noreply@blogger.com