Editing Mount St. Helens (section)

===Crater Glacier and other new rock glaciers===
{{Main|Crater Glacier}}

During the winter of 1980–1981, a new [[glacier]] appeared. Now officially named [[Crater Glacier]], it was formerly known as the Tulutson Glacier. Shadowed by the crater walls and fed by heavy snowfall and repeated snow avalanches, it grew rapidly ({{convert|14|ft|m}} per year in thickness). By 2004, it covered about {{convert|0.36|sqmi|km2|2}}, and was divided by the dome into a western and eastern lobe. Typically, by late summer, the glacier looks dark from rockfall from the crater walls and ash from eruptions. As of 2006, the ice had an average thickness of {{convert|300|ft|m|-2}} and a maximum of {{convert|650|ft|m|-2}}, nearly as deep as the much older and larger [[Carbon Glacier]] of Mount Rainier. The ice is all post-1980, making the glacier very young geologically. However, the volume of the new glacier is about the same as all the pre-1980 glaciers combined.<ref name="Brugman81">{{cite report |last1=Brugman |first1=Melinda M. |first2=Austin |last2=Post |author2-link=Austin Post (photographer) |id=USGS Circular 850-D |title=Effects of volcanism on the glaciers of Mount St. Helens |website=United States Geological Survey |url=https://pubs.er.usgs.gov/publication/cir850D |year=1981 |page=22 |access-date=2007-03-07}}</ref><ref name="Wiggins02">{{cite journal |last1=Wiggins |first1=Tracy B. |last2=Hansen |first2=Jon D. |last3=Clark |first3=Douglas H. |title=Growth and flow of a new glacier in Mount St.&nbsp;Helens Crater |journal=Abstracts with Programs |publisher=Geological Society of America |volume=34 |issue=5 |page=91 |year=2002}}</ref><ref name="Schilling04">{{cite journal |author1=Schilling, Steve P. |author2=Carrara, Paul E. |author3=Thompson, Ren A. |author4=Iwatsubo, Eugene Y. |title=Posteruption glacier development within the crater of Mount St.&nbsp;Helens, Washington, USA |journal=Quaternary Research |volume=61 |issue=3 |pages=325–329 |publisher=Elsevier Science (USA) |year=2004 |doi=10.1016/j.yqres.2003.11.002 |bibcode=2004QuRes..61..325S|s2cid=128528280 }}</ref><ref>{{cite journal |last1=McCandless |first1=Melanie |last2=Plummer |first2=Mitchell |last3=Clark |first3=Douglas |title=Predictions of the growth and steady-state form of the Mount St.&nbsp;Helens Crater Glacier using a 2-D glacier model |journal=Abstracts with Programs |publisher=Geological Society of America |volume=37 |issue=7 |page=354 |year=2005}}</ref><ref>{{cite web |author1=Schilling, Steve P. |author2=Ramsey, David W. |author3=Messerich, James A. |author4=Thompson, Ren A. |id=USGS Scientific Investigations Map 2928 |title=Rebuilding Mount St.&nbsp;Helens |url=http://pubs.usgs.gov/sim/2006/2928/ |date=2006-08-08 |access-date=2007-03-07 }}</ref>

From 2004, volcanic activity pushed aside the glacier lobes and upward by the growth of new volcanic domes. The surface of the glacier, once mostly without crevasses, turned into a chaotic jumble of [[icefall]]s heavily criss-crossed with [[crevasse]]s and [[serac]]s caused by movement of the crater floor.<ref name="VR">{{cite report |url=http://www.fs.fed.us/gpnf/mshnvm/volcano-review/documents/Volcano_Review_2008_Final_lowrez-201.pdf |title=Volcano Review |archive-url=https://web.archive.org/web/20080626134702/http://www.fs.fed.us/gpnf/mshnvm/volcano-review/documents/Volcano_Review_2008_Final_lowrez-201.pdf |archive-date=2008-06-26 |publisher=[[US Forest Service]]}}</ref> The new domes have almost separated the Crater Glacier into an eastern and western lobe. Despite the volcanic activity, the termini of the glacier have still advanced, with a slight advance on the western lobe and a more considerable advance on the more shaded eastern lobe. Due to the advance, two lobes of the glacier joined in late May&nbsp;2008 and thus the glacier completely surrounds the lava domes.<ref name="VR"/><ref name="SE">{{cite AV media |medium=photo |title=MSH08 aerial: New dome from north 30&nbsp;May 2008 |url=http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/MSH08/MSH08_aerial_new_dome_from_north_05-30-08_med.jpg |archive-url=https://web.archive.org/web/20080626134704/http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/MSH08/MSH08_aerial_new_dome_from_north_05-30-08_med.jpg |archive-date=2008-06-26 |publisher=[[United States Geological Survey]] |first=Steve |last=Schilling |date=2008-05-30 |access-date=2008-06-07}} – Glacier is still connected south of the lava dome.</ref><ref name="NT">{{cite AV media |medium=photo |title=MSH08 aerial: St.&nbsp;Helens crater from north 30&nbsp;May 2008 |url=http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/MSH08/MSH08_crater_glacier_arms_touching_05-30-08_med.jpg |archive-url=https://web.archive.org/web/20080626134705/http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/MSH08/MSH08_crater_glacier_arms_touching_05-30-08_med.jpg |archive-date=2008-06-26 |publisher=[[United States Geological Survey]] |first=Steve |last=Schilling |date=2008-05-30 |access-date=2008-06-07}} – Glacier arms touch on North end of glacier.</ref> In addition, since 2004, new glaciers have formed on the crater wall above Crater Glacier feeding rock and ice onto its surface below; there are two rock glaciers to the north of the eastern lobe of Crater Glacier.<ref>{{cite conference |author1=Haugerud, R. A. |author2=Harding, D. J. |author3=Mark, L. E. |author4=Zeigler, J. |author5=Queija, V. |author6=Johnson, S. Y. |title=Lidar measurement of topographic change during the 2004 eruption of Mount St.&nbsp;Helens, WA |date=December 2004 |bibcode=2004AGUFM.V53D..01H |volume=53 |page=1 |conference=American Geophysical Union, Fall Meeting}}</ref>