Glaciation on Shastina and the main peak of Mount Shasta occurred during the Holocene as these two cones did not exist until 9,500 and 8,000 years ago respectively. The present-day glaciers on Mount Shasta are felt to have formed during the last 4,000 years (Harris, 1988), with most of the ice build-up occurring during the Little Ice Age.

Rhodes (1975, 1987) has summarized the recent glacial history of Mount Shasta as follows. Between 1870 to 1900 the glaciers were fairly stable. A period of growth occurred between 1900 and 1916, which Rhodes refers to as the Mathes age. A drought resulted in a drastic loss of ice, perhaps as much as half, between 1917 to 1936. Wintun became stagnant during this time. Since 1936 many of the glaciers have increased in size, especially between 1944 to 1972. Wintun became an active glacier again during this period. From 1972 to 1987 the glaciers have been fairly stable but there was an increase in size in some of the glaciers due to the 1981-82 and 1982-83 winters.

Newspaper records provide a lot of information about the yearly snowfall and snowpack. A Mount Shasta Herald paper from 1933 stated that the February snowpack was 84 inches in 1930, 52 inches in 1931, 60 inches in 1932, and "more than 100" in 1933 (Simcox, 1933). Snowpack data for 1975-1997 can be viewed here. In the Redding Record Searchlight (1987) it was argued whether that year or 1977 was drier, while in 1977 the newspaper accounts compared 1977 with the 1924 season (Frank, 1977). Or Apperson, a Siskiyou County resident for 72 years, was quoted as saying, "The only thing you can say for sure is it looks like there is damn little snow this year [1987] and there was damn little in 1977" (Willis, 1987). The 1988 yearly snowpack was "far below normal" (Mount Shasta Herald, April 1988) but the local ski parks were delighted with the "phenomenal" season in 1989 (Mackie, 1989). In 1993 the "drought-ending storms left the deepest snowpack on the mountain in 10 years" (Garrison, 1993) while in 1994 the snowpack was below average (Bolling, 1994). In 1995 a twenty-year record in snowpack was recorded (Weed Press, February 1995). This year (1997) the snowpack is "unusually deep" at the higher elevations with a higher-than-normal water content and "thick layers of ice" (Jennings, 1997) but the lower elevations have little snow due to the remarkable amounts of rain, as shown in this 1996 article from the Siskiyou Daily News:

Mount Shasta City shatters 109-year rainfall record

MOUNT SHASTA CITY, December 31

       Mount Shasta City's 109-year-old record for December rainfall was shattered Monday after almost an entire day of rain.
       According to Frank Christina, a weather monitor for the city, 3.10 inches of rain had fallen in Mount Shasta in the last 24 hours as of 5 p.m. Monday, "and it's still pouring."
       The constant rain, Christina said, brought December's rainfall total to 19.69 inches, with one day still to go.
       The old record, set in Dec. 1888, was 17.48 inches, Christina said. According to the weather watcher, December's rainfall for the town has been "phenomenal," breaking five daily records.
       "The rain is still coming down in sheets," Christina said late last night. Depending on today's rainfall in Mount Shasta, he said, the city's annual precipitation total may approach another significant record.
       If December's rainfall total exceeds 21.73 inches, Christina said, it would make this month the second wettest in all recorded history. Jan. 1995, still holds the record with 27.5 inches.
       Medford, Ore., also saw record-breaking rainfall, making 1996 the wettest year on record.
       According to the Medford Mail Tribune, the city had a total of 30.54 inches of rain for 1996, breaking 1983's record of 30.15 inches.
       The National Weather Service forecasts rain and showers will continue through the weekend for much of the state.

During the last 500 years there has been numerous jökulhlaups, or glacial outburst floods (Finch and Anderson, 1928; Hill, 1984; Osterkamp, Hupp, and Blodgett, 1986; Biles, 1989; Miesse, 1993). These are due to the melting of glaciers during the late summer often combined with temporary blockage of the channel. When the temporary dam breaks apart, the meltwater is released and rapidly flows downslope. Because Mount Shasta has thick layers of ash which readily erode, the meltwater quickly becomes thick, like wet cement, and can carry huge boulders. Jökulhlaups will be discussed after the recognized glaciers of Mount Shasta are summarized.