VOLCANIC PROCESSES ESS 462
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Date Created: 09/09/15
False starts vs false alarms De nitions General public de nitions False alarm when a feared and forecast event doesn t occur no matter what the reason A distinction between false start and false alarm False start when magma is rising and then stalls without eruption False alarm when scientists misinterpret data and sound an unnecessary alarm Probabilities and false alarms in principle use of probabilities can alleviate the problem of false alarms about WHAT because we can have all possible outcomes covered Probabilities are less helpful re the WHEN of forecasts We can t in general estimate probabilities of eruption like 20 chance on Sunday 40 on Monday In practice the public and the press treat your highest probability events as a forecast of what will happen within a few daysweeks Case history 1 Campi Flegrei caldera near Naples Caldera with a history of moderate to very large scale explosive eruptions latest in 1538 AD Dense population throughout the caldera so any eruption would threaten many Densely populated Campi Flegrei caldera city of Naples is just over ridge at top of photo City of Pozzuoli visible w pier lower right Photo shows west half of caldera center is near Pozzuoli City of Pozzuoli The entire field of view is within the Campi Flegrei caldera Center of the caldera and of recent uplift is near Pozzuoli Macellum Serapeo Serapeo marketplace Pozzuoli Monte Nuovo 1538 Number 1500 1000 500 WAMHHEE 7 Tu 2392 1 J J l quotIll ll 3980 240 160 80 wo undn 196972 and 198285 unrest Intense unrest in 196972 198285 town of Pozzuoli evacuated for months on account of earthquake damage falling masonry Given political economic and logistical realities is there an practical limit of precautions that can be undertaken regardless of risk Given the dense population is there any threshold of risk below which no actions need be taken If using PvsN criterion of acceptability In Campi Flegrei population N is high so only low probabilities of eruption P can be acceptable Using P vs N and an upper limit of say P0001 of 50 deaths in Campi Flegrei will require early evacuation quite possibly before it s certain that an eruption will occur or from which ventsl And thus increase the chance of false alarms Case history 2 Long Valley CA Unrest began in 1978 really noticed May 25 1980 onward 4 M6 eqs just 8 of caldera 2530 cm upli from 19781980 continued through 90 s still a little today On basis of seismicity and uplift Notice of Potential Volcanic Hazard issued in 1982 Premature release of cials and people blindsided Time of high interest rates and thus decreasing condo values Anger directed at scientists US Guessing Society By late 80 s and 90 s anger turned to acceptance thanks in signi cant part to Dave Hill 50 Miles o 19 20 an no so 5 7o KinMerl 1 Tug UPLIFT f LENGTH CHANGE mm 700 800 61 O O 400 a O O 200 1200 IIIIIIIIIIIHIIIIIIIHIIIIIIIIIIHIIIIIIIIHIIIIIIIIIIIIIIIIIIIIIIIIIIII Cumul of Sierra Nevada quakes Mgt3 1 r g7 3 Iquot 1978 198 Max uplift since 1975 mm a Cumul of Caldera quakes Mgt3 1000 39 800 0 1871 I19le 98 ll196i 198 39193L ll1994L 199 I199l II199L 09 I TIME YEARS 2000 IIMHIATI E NUMBER Mgt5 EVENTS quot i 39 i g V 7 r a fig Ml la 3quot 5 q LINE I39I Er Emmi ai39iunr m i Lra39 Mml ur lg 39 HANGE mm UPLIFT f LENGTH 990 1200 E a i 700 E 739 71000 E 7 300 5 Sierra Nevada Mgt3 V airmar E 0 397 quotif E I 900 500 E r Coso Krokc oc Baseline 3 9 2 C0lorEDMc1rc1 I a 9 409 3 600 E f39 y f E Caldera Mgt3 39 300 j E Uprirr since 1975 400 200 E Levelrng Doro E In 0 E 85 g 7200 190 E 9 1 E 8 339 3 V 0 O O 2 19751983 19844989 19904995 c n 0 197 199 199 19 199 199 19 199 199 199 199 2000 W39LJ39L39LMHUL 392 TIME YEARS C IIMUIATI E NUMBER Mgt5 EVENTS I we 3 1 VU I I I I x Inrlu on source 37 45 N ONG VALLEY CALDE ma a lx Dike 5 ngsurgem Dome V z 740 km 40 Mamm39rh lt9 1 v 39 MTn e 1 x 39 t g 1m1 3539 Deep LP earthquakes Q 39 and C02 source 3574 z 1010 25 Km I QgC J I 39 If 6740 so I 11 7lt 4gt e 45 2539 4 RR 10 Miles 10 KM 39 39 l 39 39 39 539 119 5539 50 3539 30 Case history 3 Tungurahua Volcano and Ba os town Ecuador Anhazer Quito Tungurahua Chronology Latest eruption of Tungurahua 19161918 including pfs Quiet since then SeptOct 1999 eqs and strong tremor so town evacuated Eruption began as forecast but has been benign strombolian 1999present Some looting caught on TV Townspeople ran out of patience after few weeks in 1999 stormed barricades and were home before Christmas With continuing eruption and degassing trend of magma will probably be toward higher viscosity and VB Tungurahua Questions The conduit is open and its magma is convecting Mll there be warning of the rst pyroclastic ow Even if there is warning of imminent pyroclastic flows will the people of Ba os ever leave again The ultimate false alarm dilemma Vesuvius f 39 Veswius as seen from SW industrial area of Naples Herculaneum at right Pompeii behind volcano at right Jarg Alean Napoli Rompeii Ercolano and VGSUViO Part of Campi Flegrei caldera and Pozzuoli visible at far left It s i39 almost too late for land use plans fag being demolished and owners compensated Situation and emergency plan gt 1 million people living inside area swept by pyroclastic surge in 79 AD VEI 5 600000 in area swept by 1631 VEI 4 Close working relationship between Civil Defense and most volcanologists For emergency planning 1631 eruption is taken as model Per the present plan which may be revised 600000 will be evacuated and moved throughout Italy Evacuation will require 2 weeks BUT How long before an eruption might precursors begin think of MSH Pinatubo i How long before an eruption will an eruption be practically certain ie with events on an irreversible trend toward eruption think of Rabaul Pinatubo How certain will scientists be 2 weeks before eruption What to do at Vesuvius Consider staged andor voluntary evacua ons Consider pf barriers andor right in the communities IMHO a bad idea Engage populace in dialogue re this timing dilemma and re tradeoff between risk and false alarms piearrange safe passage asylum for scientists in case the volcano doesn t erupt Tips useful at all volcanoes Engage of cials and citizens in dialogue on tradeoff of warning lead time vs certainty 1 chance of false alarm Encourage discussion of acceptable risk and its relation to false alarms The more risk a society is willing to accept the fewer will be the false alarms Conversely if of cials demand zero risk then they d better expect false alarms