Launch Window at Corbin Point: Planning for Tsunamis

Mission Planning Briefing: Hazards at Corbin Point

1A space agency plans to launch a new weather satellite from Corbin Point, a launch site on a low, flat stretch of the Pacific coast of the United States. The rocket is put together in a tall assembly building and then rolled out to a launch pad about 400 m from the shore. Before the launch window opens, hazards officer Ms. Ingrid Okonkwo-Hale briefed the mission team, along with seventh graders Dmitri Vasquez and Laleh Ferreira from the agency's student mission program.

2Ms. Okonkwo-Hale explained that most large tsunamis start with a large earthquake under the seafloor. When a block of the seafloor suddenly moves up or down, it lifts or drops the water above it, and waves spread out across the ocean in all directions. In the deep ocean, a tsunami travels about as fast as a jet plane but is often less than 1 m high, so ships may not notice it. As the waves reach shallow water near shore, they slow down and grow taller. A tsunami is a series of waves that can keep arriving for several hours, and the first wave is often not the largest one.

3Table 1 lists every tsunami recorded at Corbin Point in the last 100 years. The travel time is the time from the earthquake to the first wave at Corbin Point.

4To forecast tsunamis, the agency uses several tools. Seismometers around the Pacific find an earthquake's location and size within about 5 minutes. Pressure sensors on the deep seafloor measure tiny changes in sea level as a tsunami passes above them, and a buoy relays their readings to a satellite. A tide gauge at Corbin Point measures the water level at the shore. The launch site has a sea wall that holds back waves up to 1.5 m high. Workers on foot need about 25 minutes to reach high ground on the hill road, but a concrete tsunami tower 300 m from the pad can be reached in about 4 minutes.

5The briefing ended with one more risk. A fault on the seafloor about 150 km offshore can also cause earthquakes, and Tsunami F came from it. The shaking from an earthquake on that fault would be felt strongly at Corbin Point.