Loess (wind-blown silt) Loess Hills (lower Mississippi basin) http://www.backyardnature.net/loess/geology.html Terracotta soldiers of Xian, China (buried in loess from Gobi Desert) http://www.moregruel.net/gallery/xtw?page=2 Slide 2 Alluvial fan (Death Valley, CA) http://www2.nature.nps.gov/geology/usgsnps/deva/rfan.html Very coarse, high K, high n, but water table often at great depth. (Water drains right through) Slide 3 Braided river gravel deposits make excellent aquifers! Chitina River, Alaska (from Press & Siever, 1998) River gravel Slide 4 Meandering river Near Anchorage, Alaska From Press and Siever (1998) sand bar silt and clay Slide 5 http://www.mbarron.net/Nile/sat-delta.jpg Delta: mainly fine sand, silt and clay low-med K units mostly Slide 6 Glacial deposits http://mantei.smsu.edu/glg110/glaciers.html (till) In front of the end moraine, glacial meltwater reworks the till and forms broad sheetlike deposits of sand & gravel (outwash plain). Excellent aquifer. Slide 7 Glacial till forms a blanket-like deposit beneath a glacier. Till usually consists of boulders in a finer matrix of silt and clay. It will usually have low K unless the deposit has been reworked by wind or water. http://mantei.smsu.edu/glg110/glaciers.html Slide 8 Lateral and medial moraines (Press et al.) http://www.zephryus.demon.co.uk/geography/resources/glaciers/moraine.html#top Moraines form at the edges and terminus of alpine or continental glaciers. They are rich in boulders and gravel, and if re-worked by rivers or glacial meltwater (or ocean currents) they can be very good aquifers. Slide 9 End moraines Long Island, N.Y. is a good example of highly permeable sands & gravels left behind as a recessional end moraine near the end of the Wisconsin ice age The Oak Ridges Moraine (ORM) near Toronto is another end moraine. This gravel deposit has a unique habitat of wetlands and fresh lakes, and is also an important gw supply for metropolitan Toronto. http://www.conncoll.edu/ccrec/greennet/arbo/publications/34/CHP1.HTM Slide 10 Press et al. Eskers are rivers of sand and gravel that formed when a meltwater channel beneath a continental glacier fills with sediment. They are excellent sources of gw, but are limited in size. Commonly mined for gravel. Slide 11 Glacial lake sediments (glacio-lacustrine) Glacial lake sediments typically contain a lot of clay, but may be interlayered on a cm scale with sand and silt. The layers are called varves, and reflect alternating seasons. In winter the lakes and surrounding rivers are frozen, and clay is deposited. In summer, swollen rivers dump silt & sand into the lakes. Slide 12 Open-system pingos form when groundwater flows downhill and is trapped underneath the permafrost. Eventually the water forces itself up through cracks into the permafrost and freezes, pushing the soil above it up into a dome Pingos http://www.taiga.net/yourYukon/col171.html Slide 13 Prince Edward Island Bedrock = redbed sandstone and conglomerate (Carboniferous age) PEI gets 100% of its drinking water from gw in the fractured sandstone. They have abundant supplies. Total use is < 2% of total annual recharge. Main problems related to pollution. Slide 14 Press et al., Understanding Earth Limestone karst features Slide 15 http://www.imperialtours.net/karst_scenery.htm http://www.siue.edu/GEOGRAPHY/ONLINE/MGfig5.jpg tower karst in China (near Guilen) tower karst in Thailand Slide 16 http://water.usgs.gov/ogw/karst/karstphotos.htm USGS hydrogeologist injecting rhodamine dye to see where water in a sinking stream turns up. Slide 17 Sinkholes (collapsed cave roof) In rural areas, sinkholes are popular places to throw trash. Is this a good idea? Slide 18 http://capp.water.usgs.gov/gwa/ch_g/G-Floridan.html Floridan Aquifer Shows thickness of limestone aquifer. Brown = confined Blue = unconfined Slide 19 Light blue is high purity water. Purple is saline. Red areas show areas where Floridan aquifer has been drawn down from withdrawels. Slide 20 Edwards Aquifer (south Texas) http://www.edwardsaquifer.net/geology.html Slide 21 Igneous and metamorphic- rock aquifers at or near the land surface. Limit of continental glaciation. North of this line, glacial sand and gravel aquifers overlie bedrock aquifers in many places. Includes Columbia River and Snake River flood basalts http://capp.water.usgs.gov/aquiferBasics/volcan.html Pacific NW basalt-rock aquifers Slide 22 During cooling, basalt flows develop characteristic fracture patterns that increase K and n of rock. K is also increased by interflow sediments (loess, sand) and lava tubes/tunnels. A lava tube Slide 23 Columnar joints in andesite lava flow (Patagonia) and in a sub-volcanic intrusion Devils Tower, Wyoming In general, lava flows and welded tuff have higher permeability than non-welded pyroclastic rock (tuff and ash). Much of the porosity is fracture or joint-controlled. Non-welded tuff doesnt fracture easily, and can have a very high clay content. Layers of ash that fall 100s of miles from the volcano can compact to form very low-K confining layers surrounded by otherwise hi-K sediments. Slide 24 Welded tuff (fractures easily good secondary permeability) Non-welded tuff (Very low K this tilted outcrop is being mined for bentonite, or swelling clay) Pyroclastic volcanic rock Slide 25 http://geoweb.tamu.edu/courses/geol101/heaney02/Chapter5/sld016.htm For plutonic and metamorphic rocks, gw storage and permeability is totally controlled by presence or absence of secondary fractures. Look for lineaments from air photos for location of major faults or fracture zones that have higher gw yield. Slide 26 http://geoweb.tamu.edu/courses/geol101/heaney02/Chapter5/sld016.htm Humbug Spires (Butte, MT) Slide 27 Permeability of regional metamorphic rocks can be strongly anisotropic, due to development of foliation (slaty cleavage, schistosity, gneissic banding).