Hurricane Mitch – October 1998 Using Natural Disasters to Teach Science Hurricane Mitch – October 1998 Hurricane Mitch was a category 5 hurricane on the Saffir-Simpson Hurricane Scale. It was the deadliest storm to strike the western hemisphere in the past 200 years. Mitch had sustained winds of over 155 mph with gusts of up to 200 mph, and it stirred up waves on the Caribbean coast estimated to be as high as 44 ft. Mitch made landfall on the coast of Honduras on the 29th of October. The storm produced enormous amounts of rain as it interacted with the mountains of Central America. Rain fell at a rate of 1 to 2 feet per day, with total accumulations of 75 inches in some areas. This is a satellite image (colorized IR) of hurricane Mitch as it approached the coast of Honduras.

Using Natural Disasters to Teach Science Destruction Caused by Hurricane Mitch in Honduras Hurricane stalled over the mainland October 29 - 31 1998. 7,000 fatalities 33,000 homes destroyed 95 bridges destroyed 70% of road network damaged Overview of damage by Hurricane Mitch in Honduras only. Most of the damage was caused by rainfall associated with the hurricane, as opposed to high wind speed.

Flooding Caused by Hurricane Mitch Destroyed housing Flood-inundated area Destroyed agriculture Here is an aerial photograph of the city of Choluteca, southern Honduras, showing how high floodwaters rose in the city and resulting damage to homes and crops. We will be doing a similar exercise using a lidar-generated map of Tegucigalpa, Honduras. Tributary Rio Choluteca

Using Natural Disasters to Teach Science Landslides Caused by Hurricane Mitch The heavy rain resulting from Hurricane Mitch also caused many landslides. The photograph above shows a close-up view of an area buried by a debris flow. Truck for scale. The woman is standing next to a cross that marks where someone was killed by the debris flow. The yellow sign says “DANGER.” Notice the steep hill in the background that has been cleared of trees to provide agricultural land. Deforestation increases the instability of steep slopes and the likelihood of landslides.

Using Natural Disasters to Teach Science El Berrinche Landslide Scar (looking south) A close-up view of the part of Tegucigalpa devastated by the debris flow from El Berrinche landslide. Note the dense housing on either side of the landslide scar. Before the landslide, housing filled the area now that is bare. At the base of the landslide scar you can see terracing of dirt that was excavated from the landslide-derived debris dam formed in the riverbed. This dirt was excavated from the riverbed and terraced to stabilize the hillslope by the U. S. Army Corps of Engineers

Using Natural Disasters to Teach Science Cross Section and Lidar Map of El Berrinche Landslide in Honduras (map view to west) The three-dimensional lidar image of central Tegucigalpa shows the Rio Choluteca in the foreground and El Berrinche landslide scar on the hill slope. Colonias (colonies) have sprung up along the flanks of the hill. Colonia Soto once stood where the landslide occurred. The landslide is clearly evident where vegetation and housing have been smoothed away. Luckily the initial movement of the landslide was slow, allowing inhabitants of Colonia Soto to evacuate. Show location of U. S. Army Corps of Engineers stabilization “benches” to tie into previous slide. Note cross section (left) from top to bottom of hill (left to right) of slope along which landslide debris slid into the riverbed and blocked the flow of the river, flooding the surrounding city. We will use another lidar map to simulate flooding that resulted when the debris from El Berrinche landslide dammed the river.

Using Natural Disasters to Teach Science Lidar : Light Detection and Ranging Lidar is an acronym for light detection and ranging. Other similar acronyms are radar (radio detection and ranging) and sonar (sound detection and ranging). Lidar instruments can be mounted on satellites, the space shuttle, or small aircraft (as shown here), or they can be used on the ground (yellow instrument shown here).

Using Natural Disasters to Teach Science Review of Lidar Principles Scanning mirror sweeps laser beam across the ground Range to target is determined by measuring time interval between outgoing and return of reflected laser pulse Aircraft position is determined using GPS phase differencing techniques Pointing direction of laser determined with Inertial Measuring Unit (IMU) and recording of mirror position Data streams recorded and synchronized to process Explain how Lidar works…. Three data streams: (1) Laser ranges determined using knowledge of the speed of light and measuring how long it takes a single laser pulse to be transmitted and received (2-way traveltime). Remember velocity = distance per unit time and a laser travels at the speed of light (c). So, in this case, distance or range to the ground = c × (time/2). Very accurate timing devices and receivers allow lasers to fire 25,000 times per second (25 kHZ or kilohertz). GPS – global-positioning-system post processed differential solution for the plane allows researchers to know the position of the plane with respect to the ground within 5 to 15 cm in x, y, and z directions. IMU – inertial measuring unit allows researchers to determine the attitude of the airplane as it flies through the sky. This motion greatly affects pointing direction of the laser. The IMU is composed of sets of three accelerometers and three gyroscopes mounted orthogonally. Because IMU’s are also used to guide cruise missiles, they are regulated by the U. S. Department of Defense.

Using Natural Disasters to Teach Science Lidar Flight Lines over Tegucigalpa, Honduras Survey area Flight lines Flight lines, which are tracks of the airplane as it flew over Tegucigalpa, are shown by the yellow lines. You can see that much time is spent turning around for the next flight line. The base map is a conventional topographic map. The survey area (outlined in blue) measures 10 km × 10 km.

Using Natural Disasters to Teach Science Result of Lidar Mapping Two-dimensional map of Tegucigalpa, Honduras El Berrinche landslide scar shown by black dotted line Colors show elevation of land surface in meters Map is about 3000 m (3 km) wide by 3200 m (3.2 km) tall. Here is a two-dimensional map derived from lidar data collected in Tegucigalpa, Honduras. Note that because data are in digital format, we can change colors and perspective. We will use a similar map to simulate flooding that resulted when the Berrinche landslide (shown by black dotted line) dammed the river.