How tall are you really? Establishing Mount Shasta's summit elevation in the 20th century
There are a couple of ways to make a volcano shorter: it could have an eruption or a debris avalanche, or it could simply erode over time. Or, it could get lose height on paper! While both of the former have occurred at Mount Shasta in its geologic history, the latter was to blame for an elevation change in the early 20th century.
Following a 1904 topographic survey of California, the U.S. Geological Survey revised the mountain's height from 14,444 feet (4,403 m) to 14,380 feet (4,383 m). This was a bit of a surprise, and prompted a short article in the Chico Weekly Enterprise newspaper in February 1906 which attempted to explain the loss:
"The altitude of Mount Shasta is commonly given at 14,444 feet - a number easily remembered - but the United States Geological Survey has recently established the altitude at 14,380 feet, or 64 feet less than formerly. This loss is accounted for, however, by the numerous eruptions that have taken place within a year in the vicinity of Sisson [Mt. Shasta]. So much has oozed out at the mud springs in Sisson and so much of the old mountain has been ripped off by snowslides that the peak has settled on its base and shrunk... (Chico Weekly Enterprise, No. 8, February 16 1906)"
(Ironically, the 1906 stereograph here reduces Shasta's height to 14,442 feet - though this is probably a typo. Image courtesy of the Library of Congress, https://www.loc.gov/item/94505701/)
To a layperson at the time, this might have seemed like a reasonable explanation. But while the "mud springs" were a real occurrence in 1905 (see https://www.usgs.gov/observatories/calvo/news/curious-case-mount-shasta…), there would have been no connection between either them or snow avalanches and Shasta's height. There were also no landslides large enough to have affected the summit elevation - the mud was probably coming from drainages that are well-known for their debris flows. In reality, advancements in survey techniques, rather than any physical change to the mountain, caused the decrease. Today, even more sophisticated satellite elevation mapping has established Shasta's height at 14,163 feet (4,137 m) above sea level. And unless significant landslides were to remove a portion of the summit - something that is very unlikely to happen - Shasta will remain at its current height.
Read the original 1906 Chico Weekly Enterprise article at https://cdnc.ucr.edu/?a=d&d=CWE19060216.2.10, and about the history of the USGS Topographic Division mapping efforts at https://pubs.usgs.gov/circ/1341/pdf/circ_1341.pdf
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