Editing Mount St. Helens (section)

===Smith Creek and Pine Creek eruptive periods===
A dormancy of about 4,000&nbsp;years was broken around 2500&nbsp;BC with the start of the Smith Creek eruptive period, when eruptions of large amounts of ash and yellowish-brown pumice covered thousands of square miles.<ref name=Harris1988/>{{rp|page=215}} An eruption in 1900&nbsp;BC was the largest known eruption from St.&nbsp;Helens during the [[Holocene]] epoch, depositing the [[Yn tephra]].<ref name=Harris1988/>{{rp|page=215}}<ref>{{cite journal |last1=Pallister |first1=John S. |last2=Clynne |first2=Michael A. |last3=Wright|first3=Heather M. |last4=Van Eaton |first4=Alexa R. |last5=Vallance |first5=James W. |last6=Sherrod |first6=David R. |last7=Kokelaar |first7=B. Peter |title=Field-Trip Guide to Mount St.&nbsp;Helens, Washington: An overview of the eruptive history and petrology, tephra deposits, 1980 proclastic density current deposits, and the crater / Eruptive history |journal=Scientific Investigations Report |page=11 |publisher=[[United States Department of the Interior]] |year=2017 |issn=2328-0328}}</ref> This eruptive period lasted until about 1600&nbsp;BC and left {{convert|18|in|cm}} deep deposits of material {{convert|50|mi|km|-1}} distant in what is now [[Mount Rainier National Park]]. Trace deposits have been found as far northeast as [[Banff National Park]] in [[Alberta]], and as far southeast as eastern [[Oregon]].<ref name=Harris1988/>{{rp|page=215}} All told there may have been up to {{convert|2.5|mi3|km3}} of material ejected in this cycle.<ref name=Harris1988/>{{rp|page=215}} Some 400 years of dormancy followed.

St.&nbsp;Helens came alive again around 1200&nbsp;BC—the Pine Creek eruptive period.<ref name=Harris1988/>{{rp|page=215}} This lasted until about 800&nbsp;BC and was characterized by smaller-volume eruptions. Numerous dense, nearly red hot pyroclastic flows sped down St.&nbsp;Helens's flanks and came to rest in nearby valleys. A large mudflow partly filled {{convert|40|mi|km}} of the Lewis River valley sometime between 1000&nbsp;BC and 500&nbsp;BC.