Finish Volcanoes. Ash/pyroclastic flow and mudflow (lahar) layers along Toutle River going back several thousand years, showing. areas now settled.

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1 Finish Volcanoes Mudflows caused by melting snow and glacier ice created extensive damage on tributaries coming off of Ste Helens, several miles downstream. Here trees and equip jumbled in mud flow on Toutle River. lahars are a common hazard with volcanoes with seasonal snow cover or glaciers. Pre-eruption hazard map laid out mostly concentric risk areas, plus linear mud flow and flood zones down the rivers leading from the mountain. In 1980 eruption blast extended much further than red zone to north, and mud flows did indeed work well down the rivers, especially the Toutle (previous slide). The US Army Corps of Engineers building a sediment retention structure on the Toutle River to catch ash/mud/sediment coming off of the mt and out of the extensive blast area---greater sediment will come down thru the systems for decades. The Toutle dumps into the Columbia, thus posing a problem for navigation. This sediment trap will fill and new ones may need to be built depending on the amount of material that comes down the drainage. New surface deposits map of Ste Helens indicates future risks, and shows most pyroclastic deposition (0range) spread out to the north by the lateral blast. Ash/pyroclastic flow and mudflow (lahar) layers along Toutle River going back several thousand years, showing frequent prehistoric activity in areas now settled. Volcano Risk Assessment: The standard frequency/magnitude approach to assessing volcanic risk is problematic: events are rare and clumped. Still, data are getting better: In this example of the Cascades eruptions (frequency or probability) in the U.S., what volcanoes would you worry about the most? Ste. Helens would have looked like a good bet for trouble had this record been available before 1980, and though Rainer shows less activity than some others, it is not dormant, and offers higher risk (probability times consequence) due to large population nearby. 1

2 Hazard assessment around Mt. Rainer. Few people live in potential pyroclastic/lava/blast zone (gray), but 150,000 people live on previous Rainier lahars downstream! Lahars and floods can go way down local drainages, so: Now-Casting warning system in place on Puyallup and Carbon rivers: senses mudflows coming down the river and sends out an alarm, this is then sent via reverse-911 to downstream homes/businesses. Volcanologists have developed a ranked warning system for volcanic eruptions, which is applied case-by-case, around the world when and if they can get sufficient monitoring on a vol that becomes more active. About 20 volcanoes around world with very highest risk have extensive monitoring to allow some alert to nearby residents, at least now casting Careful monitoring of: Sesimicity Ground deformation Thermal changes Geochemical changes May give some clues to coming eruptions, but forecasting is difficult, and many false positives when increase seismic activity does not lead to an eruption. Volcano Hazard Reduction Challenges Monitoring, Forecast and Warning: still uncertain, caseby-case, slowly developing technology and skill. Freq/magnitude and risk analysis: difficult because eruptions are rare; geological data getting better (see slide of Cascade eruption history) Hazard zone determination/mapping: getting easier with geological mapping of past deposits from pyroclastic flows and lahars, but remember Ste Helens blasting sideways. Land use planning: same as other hazards---difficult to get people to change land use for unlikely event. Most volcano hazard zones gaining population, but still most volcanoes (with famous exceptions) in less populated areas. Chap. 9: Severe Storms: Tropical Cyclones (Hurricanes) We start severe storms (and focus on) tropical cyclones (aka hurricanes in Atlantic basin; typhoons in the Pacific; and cyclones around Australia) Main hazards: Wind, storm surge, rain (flooding), and embedded tornadoes. Exposure: About 15% of global population is threatened, on cycloneprone coasts. Perhaps 6,000/year fatalities, but most in single, extreme storm surges and floods (maybe 300,000 in 1970 Bangladesh storm surge, and 14,000 in 1998 Hurricane Mitch floods in central America) $10b annual damages (1995 dollars) with individual storms (like Katrina) approaching or surpassing $100B in today s dollars. Growing exposure and (maybe growing vulnerability) in U.S., Caribbean, S and SE Asia, Australia. Recall: Exposure vs. vulnerability: exposure is simply all property and population at risk; vulnerability is proportion likely to be damaged per event. Rapidly increasing exposure (see slide of Pompano Beach) could yield increasing losses even with decreasing vulnerability. Themes Measuring, monitoring, warning, evacuation systems Hurricane risk assessment Physical protection, & ways to decide how to deploy protection (exercise 2 covers one approach to risk and protection decisions) Building and land use mitigation 2

3 I ve highlighted main hazard zones on this map from your text places where probability, conditions, and exposure of growing populations make risk high. Physical Cause Tropical lows form over 26 C (82F) ocean surfaces, often in the so-called Inter-tropical Convergence Zone (ITCZ) where the trade winds of N and S hemisphere converge. If conditions are right, the rising warm air over low-latitude, solar-warmed waters sets off a positive-feedback: Ascent causes convergence Condensation, release of latent heat causes increased buoyancy, thus increased ascent, and increased convergence Area of convergence enlarges, more water vapor to draw on Spin imparted by Corriolis Force, increases convergence, ascent, and buoyancy, so winds speed up Centrifugal and centripetal forces come into balance (also creating the infamous eye wall); Input and output balance: low level inflow to low pressure, upper level outflow (from high pressure) and storm can reach a steady-state Decay: Loss of energy (water vapor); loss of upper air divergence; friction of land. How Intensity is Measured The mature storm is drawing in warm, moist air from a large area, into the tightening counter-clockwise spiral (in N hemisphere), then up in the wall cloud and out with upper level divergent clockwise outflow. The eye is distinct as the one area of concentrated sinking air in the system (sinking warms and dries the air, thus the eye is often clear). Like a spinning skater, the fastest spin (winds) are right near the center where the angular distance they must travel to circulate around the low are shortest. Note the circular eyewall of Andrew making landfall on SE Florida-the eyewall was barely 35 miles in diameter and most of the damage was where it passed. Wind speed: 33 m/s (74 mph) arbitrary threshold for hurricane measured by surface equipment, aircraft, or estimated from radar and satellite loops. Central pressure: commonly inches or less (30 is normal sea level pressure) Storm surge: height (1-8 m; ft above the normal tide; Also: Wave heights; total rainfall and rainfall rates; inland flood heights Saffir- Simpson Category Maximum sustained wind speed mi/h m/s kt Minimum surface pressure mb greater than 980 (28.94 inches) less than 920 (27.17 inches) Storm surge ft m How Monitored, Tracked, and Forecast The Saffir-Simpson scale puts all the magnitude measures together into five categories, a practice common in many hazards now (from earthquakes to snowstorms) but one that does give up some detail and specificity of magnitude. Wind an pressure is often mentioned in news: Cat 5 Wilma was most intense ever measured: central pressure of 882 mb or inches! (with estimated 175 mph sustained winds). Visible satellite image: spiral bands of convection, wall cloud around somewhat cloudy eye, plus outflow cirrus clouds. 3

4 How Monitored, Tracked, and Forecast How Monitored, Tracked, and Forecast Infrared satellite image shows cloud top temperatures: higher are colder, colored red; higher clouds is sign of stronger storm. Outflow cirrus especially vis to north. Radar bounces off of precipitation, which is most intense in eyewall and feeder spiral bands. dbz is measure of radar beam reflectance. See this in motion: How Monitored, Tracked, and Forecast: aircraft reconnaissance Reccon planes prohibited from flying low levels for safety, but need data from near surface so they drop a remote weather sensor that telemetries pressure, humidity, wind, etc. as it falls. In future NOAA hopes to deploy pilotless drones to fly around inside hurricanes, esp. near the ocean surface to measure the flux of energy from ocean into the storm. Katrina s eye wall from recon aircraft inside the eye. Risk Assessment: Exposure Hazardous geographies: low-lying, densely population coastal areas: Bangladesh: low gradient deltaic area with little refuge, subject to cyclones in Bay of Bengal (only about 5/year) 1970: 300K deaths, $75 million, due mostly to storm surge (3-9 m) 1991: another strike, this time 139K deaths in 6 m surge Cyclone Sidr Nov., 2007: Approx: 10,000 fatalities: but similar to earlier storms that caused many more deaths, partly due to better warnings and short evacuations from villages to designated, raised, storm shelters. 4

5 More Hazardous geographies: Impacts: Main damage cause is: Storm Surge Islands: Philippines; Taiwan; smaller Pacific and Hawaiian islands; Caribbean Islands: Urbanized coasts of large land masses: Atlantic and Gulf of USA; China, Japan, Australia. Katrina surge near Gulfport, MS. Not many photos of storm surge as difficult for storm chasers to stay in front of it, but google storm surge videos to see what they ve filmed. Great Galveston Hurricane, 1900: storm surge was the main killer here, and still the most lethal part of hurricanes. The 1900 storm put most of Galveston Island under water, killing perhaps 10K. But many older buildings at risk, even those that have stood for a hundred years: Hurricane Camille, 1969, Gulfport, MS One way of reducing storm surge damage is to sacrifice the first floor (maybe just for parking) and build valuable space above that. An one-air floor or break-away walls allows water to flow underneath without damaging the rooms in this hotel. 5

6 Apartment building before and after Hurricane Camille, 1969, Gulfport, MS Long stretches of developed coastline are at risk from storm surge, though modern buildings may be constructed with some mitigation (e.g., parking on ground level allows surge to pass under building). Still, difficult to assess how well this will handle a major storm surge. This is near Pompano Beach, FL Surge risk assessment needed for: Long-term hazard assessment / preparation: Evacuation zones Land use planning Short-term forecast and warning The approach: collect data on past hurricanes Develop probabilities of future events Project storm surge using some appropriate model, in this case: SLOSH (Sea, Lake and Overland Surges from Hurricanes) Model: which can be run for planning and real time forecast, see an example model run for a simulated hurricane here: Storm Surge physical factors: Pressure: low pressure is higher surge Wind speed: high speed, higher surge Wind direction: blowing right angle onto land from water Wind fetch: distance wind has blown in relatively straight line across open water allows it to drag more water up against the shore Wind duration: longer time wind blows onto shore more water can pile up, more chance of surge and high tide occurring simultaneously. Shoaling: shallow bottom stretching far off-shore cause more surge than quick deepening as you go off-shore (Atlantic coast has steeper shoaling than Gulf, where surges are higher) Shape of coastline: embayments and other concave shapes focus or concentrate the water for high surges; headlands and convex shapes shed the water for lower height of surge. Speed, direction and fetch all mean surge is highest on right quadrant of a land-falling hurricane. The coastline illustrated here is also concave in shape. Forecast of surge for an actual storm is segmented into different areas with different heights a range of heights is offered to account for uncertainties in physical factors sometimes that range is quite large (e.g., 10 to 19 feet!). 6

7 Surge risk maps show area inundated by different Safir- Simpson scale hurricanes. Maps assume that each spot is just right of eye at landfall. Of course, not all areas can have that surge in a single storm, but forecasting uncertainty means larger areas are warned than actually affected. These zones can then be used to plan, decide-on and organized evacuations. 7