Glaciers are formed by the accumulation of ice and snow over thousands of years. “At higher elevations, more snow typically falls than melts,” according to the National Snow and Ice Data Center (NSIDC). When enough of this snow remains in the same area year-round it transforms into ice. “Each year, new layers of snow bury and compress the previous layers. This compression forces the snow to recrystallize, initially forming grains similar to the size and shape of sugar grains. After about a year, the snow reaches an intermediate state between snow and glacier ice, “when it is about two-thirds as dense as water.”
As these grains grow larger over time, “the air pockets between the grains get smaller, causing the snow to slowly compact and increase in density.” After many years, the weight of these accumulating layers compresses the ice into larger crystals, such that “any air pockets between them are very tiny.” The NSIDC website explains that after hundreds of years, these ice “crystals can reach the size of an adult fist.” According to NASA’s EarthData website, the resulting “crystalline structure strongly scatters blue light” causing the glacier to appear almost turquoise “because the ice absorbs every color in the spectrum except blue.”
As glaciers grow, they move by internal deformation of ice (a process known as “creep”) and “basal sliding under their own weight,” according to the NSIDC. This flow activity is accompanied by a phenomenon known as “calving” when chunks of ice “break off at the terminus, or end, of a glacier … because the forward motion of a glacier makes the terminus unstable,” according to NASA EarthData. The chunks of ice released in this manner are called “icebergs.”
Icebergs “pose a significant threat to sea lanes worldwide,” according to the NSIDC, with the Titanic disaster as perhaps the foremost example. Some of the most troubling events in recent years include an enormous iceberg more than 50 miles long and 25 miles wide that broke away from the Larsen Ice Shelf in Antarctica in 1995. Meanwhile, the largest well-documented iceberg in human history, designated B-15, calved from the Ross Ice Shelf in Antarctica in 2000. It measured an incredible 183 miles in length and 23 miles in width. After drifting in the Southern Ocean for several years, it gradually split apart into smaller chunks that continued to be spotted well into 2011. Large icebergs are carefully tracked by satellite and aerial surveys to reduce the hazards they pose to international shipping.
The United States Geological Survey reports that during the Last Glacial Maximum (about 20,000 years ago), glaciers covered some 25% of the Earth’s land area and 33% of Alaska. During this period, according to the NSIDC, “Ice sheets … covered much of the Northern Hemisphere,” including the Laurentide Ice Sheet, whose “weight created basins that now hold the Great Lakes.” Today, glaciers cover about 11% of the Earth’s land area and 5% of Alaska, and there are only two ice sheets: the Antarctic and Greenland Ice Sheets.
The Antarctic Ice Sheet covers an area approximately the size of the lower 48 states and Mexico combined, while the Greenland Ice Sheet is about three times the size of Texas. Both ice sheets average about 1 mile in thickness and together contain more than 68% of all the fresh water and 99% of all freshwater ice on the planet. The water contained in the Antarctic Ice Sheet alone would be enough to raise sea levels almost 200 feet if it were to melt.
“If a glacier as a whole has a positive mass balance, the glacier terminus advances and the glacier expands in area,” according to the NSIDC. “If a glacier has a negative mass balance, the amount of ice transferred to the terminus is not enough to offset ice melt and the position of the glacier terminus retreats and the glacier shrinks in area … With a few exceptions, glaciers in all regions of the Earth have negative mass balances. Their termini are retreating, and they are shrinking in area.”
According to the State of Global Water Resources 2023 Report published last October by the World Meteorological Organization (WMO), “[G]laciers lost more than 600 gigatons (Gt) of water [in 2023], the largest mass loss registered in the last five decades … Following 2022, 2023 is the second consecutive year in which all glaciated regions in the world reported ice loss,” reflecting significant reductions “in glacier mass that would be the highest on record (1950–2023).”
Celeste Saulo, secretary general of the World Meteorological Organization summed up the impact of ice loss by stating: “Water is the canary in the coalmine of climate change … Melting ice and glaciers threaten long-term water security for many millions of people. And yet we are not taking the necessary urgent action.”
Visit https://wmo.int/publication-series/state-of-global-water-resources-2023 to read the full WMO report.
Trey Gerfers serves as general manager of the Presidio County Underground Water Conservation District. A San Antonio native, he has lived in Marfa since 2013 and can be reached at tgerfers@pcuwcd.org.