Cov xwm txheej qub tshaj plaws tau tshwm sim hauv 1860 BC. Xyoo 1980 eruption yog qhov feem ntau kawm ntawm lub xyoo pua 2340th, tab sis volcanoes muaj keeb kwm ntev ntawm kev tawg.

Rau nws ib feem, Lub Ntiaj Teb Volcanism Program hais tias lub khob hliav qab yog tsim los ntawm kev tso tawm ntawm lava thiab pyroclastic cov ntaub ntawv ua ntej 2200 xyoo dhau los, thaum lub khob hliav qab niaj hnub yog ib qho txuas ntxiv ntawm andesite, dacite, thiab basalt fragments uas tshwm sim los ntawm ntws. Hauv 3000 xyoo dhau los, lub khob hliav qab tau txais cov qauv niaj hnub tshaj plaws. Helens tsim los ntawm volcanic eruptions, lava domes, thiab lwm yam pyroclastic ntws uas mus txog thaj av deb ntawm lub hauv paus ntawm lub roob hluav taws. Nyob rau hauv ib lub sij hawm yos mus rau 12.800 xyoo dhau los, lub khob hliav qab ntawm Mount St. USGS Volcanic Hazards Program qhia tias nws nyob ze ntawm thaj tsam subduction ntawm Juan de Fuca phaj nyob rau sab hnub poob ntug dej hiav txwv ntawm Tebchaws Meskas thiab yog qhov tshwm sim ntawm kev txav loj ntawm lub ntiaj teb crust. Txawm li cas los xij, thaum lub sijhawm Holocene nws yog qhov nquag tshaj plaws ntawm tag nrho cov roob hluav taws hauv Cordillera. Raws li United States Geological Survey (USGS), nws tsim Nws tshwm sim nyob rau hauv 4 theem ntawm eruption uas pib txog 275.000 xyoo dhau los, Txawm hais tias Smithsonian Institution Global Volcanic Activity Program qhia tias nws pib hauv 9 theem tsim 40.000-50.000 xyoo dhau los thaum lub sijhawm tawg. Piv rau lwm lub roob hluav taws hauv Cascade Range, Mount Saint Helens yog lub roob hluav taws me me. Lub roob hluav taws tau paub txog nws qhov tawg loj heev uas muaj cov hmoov tshauv loj heev thiab hu ua pyroclastic ntws. Saint Helena tshuav nws lub npe rau tus neeg sawv cev ntawm Erin Fitzherbert, txij li thaum nws yog thawj baron ntawm Saint Helena, ib tug phooj ywg zoo ntawm George Vancouver, ib tug zoo thiab xav paub explorer uas yog tus saib xyuas ntawm lub cheeb tsam ntawm lub kaum yim xyoo pua nyob rau hauv Santa Helena. Cov qauv hluav taws xob loj loj no yog ib feem ntawm Cascade Range, thiab lub xaib tau pib paub los ntawm lub npe Louwala-Clough, uas txhais tau hais tias 'lub roob hluav taws kub hnyiab,' hauv cov lus ntawm cov neeg muaj npe nrov hauv zos, ib pawg neeg hauv zos hu ua Klickitat. Nws nyob raws nraim 154 mais ntawm Seattle thiab txog 85 mais qaum teb sab hnub poob ntawm Portland, Oregon. Thaum txog 2.550 meters saum toj no hiav txwv theem, lo lus 'tam sim no' yog siv vim hais tias nws cov ntaub ntawv dav dav eruptions tau txo qhov siab ntawm no volcanic qauv. Mount Saint Helens yog lub npe hu ua volcanic volcanic tsim nyob rau hauv Scamania County, Washington State, nyob rau hauv lub Pacific Northwest Territory ntawm lub tebchaws United States of America.

Helena koj