HAZARD DESCRIPTION VULNERABILITY a Lahar Is a Debris ﬂ Ow That Originates from the Slopes of a Volcano Because Mt

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VOLCANIC LAHAR HAZARD DESCRIPTION VULNERABILITY A lahar is a debris ﬂ ow that originates from the slopes of a volcano Because Mt. Rainier has been quiet for the past 1,000 years with no indica on of change, this hazard has a low and can surge tens or even hundreds of miles downstream. A probability of occurrence. Nearly 900 proper es could be damaged or destroyed by a Case 1 Lahar. The combina on of Lahar is one of Mount Rainier’s most destruc ve hazards. Historic these impacts suggests that the region is highly vulnerable. Because a Case 1 Lahar has a low probability of occurence, evidence reveals Rainier Lahars buried large swaths of lowlands as the overall Case 1 lahar is assigned a moderate risk. far as the Puget Sound. Lahars can occur without a large volcanic erup on. Probability of Occurrence Vulnerability Risk Low High Moderate Lahars are commonly ini ated by: • Large landslides of water-saturated debris DelineaƟ on of Lahar Hazard Area • Heavy rainfall eroding volcanic deposits A Case 1 lahar origina ng from Mount Rainier is considered by scien sts to be the most appropriate scenario for • Sudden mel ng of snow and ice near a volcanic vent by hazard mi ga on planning. Case 1 lahars could be high in

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S T AR CA D IA Q McNEIL IS U LAND

STE AMB OAT HO P E A HARTSTENE ISLA ND X B ISLA ND ALCH I N PA I SS S A ISLAND TAYL O R GE L BAY A JOHNSO N N POINT E consequence and pose a major hazard to human life and D HU N TER G radiant heat or on the ﬂ anks of a volcano by pyroclas c ﬂ ows POIN T A S ITAS MI S UN SA L POIN T A P T T BAIRD E COV E N BR IS CO E L DE VILS N POIN T O I L HE AD DE ER T ANDERSON N BIG Y HA RB O R E N FIS HTRA P I A TT AMS TERDA M ED GEWATE R R Thurston County O LI T T L E BAY D D T BEA C H FIS HTR A P N WI L DC AT N CO V E A

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CO V E S TR EB LE ISLAND N SANDERSON O T R POINT E DO V ER ZANGLE R L HA RB O R CO V E T N POIN T E I E M K U K O BOST ON D O K HA RB O R property in the Nisqually River valley should the Alder and N S DO FF L EMY ER EAST E L POIN T T E ORA T LI BAY H CH AP MA N SILVE R • Breakout of water from glaciers, crater lakes, or from lakes dammed by volcanic erup ons BAY ORA BAY SPI T

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Y A BUTTERBALL I A L S Case 1 Lahar Inundation Zone BU RN S P OIN T B

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CO V E A I DEWO LF LLY CO U N TR YS ID E GULL BIGH T BU RN S BEA C H CO V E HA RB O R MA L LA R D COVE FLAPJA CK LaGrande dams fail. The Case 1 Lahar inunda on area for POIN T HOG UM

Y RD BAY YOU NG TYK LE GREEN NISQ UALLY FLATS CO V E CO V E CO V E NISQ UALL Y HEAD LD B E H LUH R BEACH C A E B D T E S D N U 101 IB ¤£ S U SQU AW B FA LLS POIN T L

IS E BEA CH NR SU Historical Occurrences and Impacts K K E SH ELL E E BU TLER C OV E N R N C E POIN T

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OLYMPIA O SH OAL W S CH NE IDE R PR IE ST Thurston County is shown on the map to the right. POIN T M ELLIS

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SE T CH F I EL D K E BU DD E LA KE R C B IN LET Case 1 Lahar Hazard Area* SUM MI T A R Y E T S LAKE I L L BI G E LO W A LA KE LO C U I SE M LA KE

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Based on the Case 1 lahar scenario, proper es along the R LA KE R HI C KS C E T LA KE R O P H C K IT EE D

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R N L S LO NG A WARD R O W C E S F M LA K E B LA KE M R A H I W C V RT H M NO E R BA R N E S LA K E E L SM I T H K SO U T H W I C K U S L H A LA K E LAKE LA K E A L E N R E ST. R D S CL AIRE E T TR O S P E R HEWITT PATTI SON common occurrence; they vary in size and magnitude and are fairly B C E RE S A E LAKE LA K E LA KE T K T Y D

S T C O CREEK HA 1 in = 4.37 miles M PATTI SON K N BE E E R LA K E S T. C LAIRE Y S E Y R D R LA KE C E CREEK LA K E S C SU S A N C R H E I W E U K K E T W E MUN N CR E

N S O K S LA K E Nisqually River Valley are the most suscep ble to lahar RI S Y K H C E I L E R A V M H PORT L ER P B TRAI LS EN D E D A C T 510 LA K E R L O

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C unpredictable. Past Cascade lahars surged nearly 45 to 50 miles per hour O H R H LA K E LU C I N D A

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W A D D D E L L H C O M IT BL O D CLEARWO OD N Y A LA K E M TE M P O R 5 S E C REEK at steep slopes and were 100 feet or more thick. Scien sts have iden ﬁ ed H LAKE S

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D D E RI S C S H VER UT E ILVER R S C S R E E PopulaƟ on and Employment in the Hazard Area E K M IM A W C

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E E R I more than 60 lahars that have originated from Mount Rainier in the past D

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R D K R D GEH RKE O Y LA K E A R V R M A A M W W LA K E FIFTE EN H T L S E I I K A I I L I D M S L L L H L S TO A IN R C D 507 MIM R I V E R C V R 10,000 years. C K LA B UV E R D E S C D T H U U Presently, nearly 2,000 residents (0.7%) and 600 employees GA CK T ES O T LA W R EN C E R S IV E O R R F LA KE E NISQ E D E S U C A H U LL T E S Y L K F E RE R C I 12 CREEK 5 V E T R E R T T UV T SC A ¨¦§ RD I W S S E PO R L W IV N EL E O L R

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9 B LAKE O 183RD AVE S 9 T W C BASS R LA K E E REICH EL E K Y LA K E W CLEAR

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(0.4%) live and work in the Case 1 Lahar hazard area. C C JA S H ME BALD HILL E D N H O LA K E E A D L S IS N N L H A R H U O B L

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CK M I O U G P Under the worst-case scenario, a lahar from Mount Rainier could pose a R K CREE I IE A E V E H RIVE R R PRA I R C D L

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U T N H U R C R C M U K R JO O E H LAK N O S K D SKOOK UM C IE O R S HUCK M N RA T A ALDER PR R H L K AT E D O L L E H M A

E R F S P S C W O N CREEK S DE F A S L C C N L R H O E U R E local threat by inunda ng the Nisqually Valley. The poten al destruc on of T L K T H ITA E D HO SP S R O E F A C C N R R HA E E E E K K

ResidenƟ al Dwellings in the Hazard Area K

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C R I T Alder and LaGrande dams would add signifi cantly to the destruc ve impact M of the debris fl ows. A more likely poten al is the displacement of water in Approximately 900 or 0.8% of the county’s residen al Document Path: P:\ThurstonCounty\Hazard_Mgt\2014-2015\Maps_Images\ChapterMaps\Lahar\lahar_County_8x11.mxd the Alder reservoir, with poten al fl ooding eff ects in the Nisqually Valley. dwelling units are located in the lahar hazard area. By 2040, There is evidence (dated to have occurred approximately 300 years ago), the number of dwelling units in the hazard area could increase to 1,000. that lahars have buried forests near what are now the City of Yelm and the Inventory of Assets and Dollar Value in the Hazard Area Nisqually Indian Reserva on. Nearly $59 million in residen al, $5 million in commercial/industrial, and $6 million in government/ins tu onal Lahars are confi ned to valley bo oms, so people can avoid them by seeking es mated property valua on is within areas at moderate to high risk. high ground given suffi cient warning. The following major bridges/routes are located within the Case 1 inunda on zone and could be adversely impacted or destroyed: State Route 507 Bridge between Yelm and McKenna, Old Pacifi c Highway, and Interstate 5 in the Nisqually Valley. There are also three railroad bridge crossings at risk.

For further informaƟ on or to view the current “Hazards MiƟ gaƟ on Plan for the Thurston Region,” visit www.trpc.org/hazards. Thurston Regional Planning Council, 2016