BEGIN:VCALENDAR VERSION:2.0 PRODID:-//wp-events-plugin.com//7.2.3.1//EN TZID:Europe/London X-WR-TIMEZONE:Europe/London BEGIN:VEVENT UID:74@cumberland-geol-soc.org.uk DTSTART;TZID=Europe/London:20230611T100000 DTEND;TZID=Europe/London:20230611T100000 DTSTAMP:20230607T123241Z URL:https://www.cumberland-geol-soc.org.uk/events/the-explosive-volcanics- of-round-how/ SUMMARY:"The explosive volcanics of Round How" DESCRIPTION:Start at 10.00am Meet at Honister National Trust Car Park NY 22 569 13531\n\nEvent Presentation\n\nExcursion Information and Registration\ n\nDave Haselden\n\nLogistics\n\nMeet at 10 am at the National Trust car p ark at Honister Pass (NY 2258 1352)\, unless the weather is poor then we s hall meet in the\nSlate Mine café. Parking is free to members\, but for n on-members it is cheaper to park in the Honister Slate Mine carpark (£5/d ay).\nThe day will entail around 6 km of walking with an ascent/descent of around 500m mainly on mountain paths and sheep tracks but\nwith sections of open fell (heathery and possibly boggy) and a stream crossing at Wharns cale Beck (stepping stones – poles will\nhelp). Depending on weather/ent husiasm etc the trip will last 4-6 hours. As of 31 May 2023 conditions wer e quite dry underfoot\nand the stream crossing straightforward.\n\nIntrodu ction\n\nThe BGS has now made the 1:10000 survey maps available online via the BGS Maps Portal. The 1:10000 sheet for Round How is\nNY21SW and is wo rth a look to see what was recorded by the survey.\nThe Round How Member [ RHM] of the Birker Fell Formation is typically described in terms of sedim entary nomenclature [e.g.\nsandstones etc]. Virtually\, if not all\, the c lasts are andesitic in composition though they vary from igneous textures to welded\nignimbrite.\nWe believe that the Round How Breccia Member is vi rtually all primary pyroclastic in nature. Hence terminology should be tuf f\,\nlapilli tuff\, etc. Our interpretation is based on the presence of ab undant impact sags\, abundant coated lapilli\, widespread ultra-fine\nrim type accretionary lapilli with rim fragments in some layers\, upper flow r egime cross-bedding\, eutaxitic textures\, and layers that\nthicken into t roughs in the manner of pyroclastic density current (PDC)/ignimbrite depos its. The troughs are rounded\, a\nmorphology compatible with erosion by py roclastic currents.\nThere is very little documentation available about th e Round How Member [RHM]. McConnell &\; Kneller [1993] provide the most \ninformation and this account appears to have been the basis for the subs equent publications mentioned here. Two localities are\nbriefly described by Tuffen [2008] and the area is covered by an excursion in ‘Lakeland Ro cky Rambles’ by Bryan Lynas [1999].\nOtherwise the member has been very briefly mentioned in the Explanation Booklet for the Keswick 1:50\,000 she et [Woodhall 2000]\nand the British Geological Survey’s British Regional Geology\, Northern England [Stone et al. 2010]. The latter two publicatio ns\nprovide little detailed comment and leave an overall interpretation of the member ambiguous. The BGS 1:10\,00 survey maps are\nnow available onl ine and provide interesting insight into the interpretation of the geology . McConnell &\; Kneller [1993] use\nsedimentary terms [sandstone\, etc. ] in describing the deposits in the member and interpret the RHM as coarse fragments formed by\nautobrecciation of an inflating\, and autobrecciatin g\, andesite lava pile\; the coarse detritus was then washed into a shallo w lake. Our\ninterpretation is that most if not all the RHM is primary pyr oclastic formed in a tuff-ring or maar like setting. The widespread\ncoate d lapilli and common accretionary lapilli suggest very moist\, low tempera ture [<\;100oC] pyroclastic currents. Virtually all of the\nlapilli are angular and have igneous textures meaning that the explosivity was created when magma encountered external water\nprobably groundwater in an aquifer . Typically this eruptive style involves decades to 100s of years between eruptions because the\nwater supply has to be replenished. Each eruption s tarted with fragments being ballistically ejected and an eruption column o f\nsufficient height to produce pyroclastic currents when the column colla psed. END:VEVENT BEGIN:VTIMEZONE TZID:Europe/London X-LIC-LOCATION:Europe/London BEGIN:DAYLIGHT DTSTART:20230326T020000 TZOFFSETFROM:+0000 TZOFFSETTO:+0100 TZNAME:BST END:DAYLIGHT END:VTIMEZONE END:VCALENDAR