Today’s plan: – Finish “Why study glaciers” – Glacier mass balance (accumulation, ablation, equilibrium line) – Ice flow – Glaciers and recent climate change Announcements: - Xhour tomorrow (5/16) – NOVA video – “Extreme ice” and exercise - Friday – Last quiz Why study glaciers? • Respond/indicate climate change: • Respond to climate and record climate • Some glaciers (ice sheets) influence climate – How? • Shaper/creator of landscapes: • Important for understanding deposits, underlying bedrock, groundwater • Storage of water: • Influence global sea level Glaciers shape the landscape through glacial erosion and deposition The Laurentide Ice Sheet ~21,000 yrs ago in North America Dyke et al., 2002 Hanover, NH https://www.treehugger.com/climate-change/xkcd-webcomic-shows-how-thick-ice-was-over- north-american-cities-21000-years-ago.html Shaper/creator of landscapes: Manhattan – glaciated bedrock Shaper/creator of landscapes: Long Island Long Island was the terminus of Laurentide Ice Sheet Made of SEDIMENT! Storage of water: Present day ice volume – potential sea level rise Geographic region Volume % Sea level (km3) equivalent (m) Ice caps, valley glaciers, 180,000 0.55 0.45 ect. Greenland Ice Sheet 2,600,000 7.9 6.50 Antarctica: 30,109,800 91.49 73.44 East Antarctica 26,039,200 64.80 West Antarctica 3,262,000 8.06 Ross Ice Shelf 229,600 0.01 Total 32,909,800 100.00 80.44 For interactive sea-level rise map see: https://coast.noaa.gov/slr/# What is Causing Sea Level to Rise Today? 5 1993-2010 Average Rates 4 Total SL Rise Rate Today: ~12 in/century 3 2 1 (Inches per 100 yrs) Sea Level Rise Rate 0 Thermal Small Water Greenland Expansion Glaciers Use Antarctica Data from IPCC, 2013, Figure from E. Osterberg Compare Sea Level Rise Today to 2100 8 1993-2010 Average Rates 7 2081-2100 Average Rates 6 Total SL Rise Rates Today: ~12 in/century 5 2100: ~21 in/century 4 3 2 (Inches per 100 yrs) Sea Level Rise Rate 1 0 Thermal Small Water Greenland Expansion Glaciers Use Antarctica Data from IPCC, 2013, Figure from E. Osterberg Range, including uncertainty, by 2100 is: ~0.3-1.0 meters ~1-3.3 feet IPCC, AR5, WG1, SPM, 2013 Glacier mass balance (bank account): Difference between ice gain (Accumulation) and loss (Ablation) • Climate – summer temperature and winter precipitation • Local topography – shading by mountains, debris from rock falls Glacier mass balance Accumulation • Precipitation: snow, freezing rain • Rime ice: freezing of super-cooled water vapor or drops • Wind drift: blown snow • Avalanches Rime ice on Mt. Washington, NH (MOUNTWASHINGTON.COM ) Ablation • Melting: at glacier surface, within pore spaces, in other voids below surface • Sublimation • Iceberg calving (80% of ablation in Antarctica occurs by calving!) Why/how do glaciers flow? • Glaciers flow in the direction in which their top surface slopes – The driving stress of a glacier is a result of its thickness and its surface slope – Ice sheets spread outward from the thickest point – Don’t care what is at the bed (Will flow “up hill”!) Why/how do glaciers flow? • Glaciers flow by two processes: – Internal (plastic) deformation – Basal sliding (if water/saturated sediment at base) Time-lapse glacier flow – Aletsch Glacier, Swiss Alps http://www.swisseduc.ch/glaciers/aletsch- livecam/index-en.html?id=0 Crevasses form where ice breaks (brittle deformation) Below at depth of ~50 m, ice deforms plastically Crevasses in Greenland glacier.