Inundation of Pago by tsunami waves. National Park of American Samoa.
Natural processes such as tsunamis, coastal landslides, and storms are driving forces of change along the coast. When combined with increasing sea levels, these events may have tremendous impacts on our coastal environments and beaches.
These processes and other coastal hazards are threatening parks’ cultural and natural resources, infrastructure, and public recreational opportunities. To effectively cope with these issues, the NPS is working to identify and meet the needs for scientific information, decision support tools, and coastal adaptation. See the articles below for an introduction to some of the coastal hazards present in parks:
Natural processes are integral in maintaining the geodiversity of coastal landscapes. They greatly contribute to the creation and transformation of our coastal landforms. Many natural hazards occur in cascading sequences which adds to their effects (e.g., earthquakes and tsunamis, coastal storms and storm surge), and many coastal hazards are becoming heightened with rises in sea level. Coastal hazards are factors that make each of our parks unique. However, these processes may become dangerous at the human-nature interface.
In certain locations, humans attempt to alter and control the coastal zone for increased public safety and property preservation, for more information see Engineering in the Coastal Environment. However, these modifications may increase storm impacts in some locations. It is important to fully understand the impacts of engineering before initiating a project.
Our park resources and structures are vulnerable to such rapid change events. In response, the National Park Service, in cooperation with various partners, is undertaking a series of investigations to assess the vulnerability of natural and cultural resources to hazards in coastal parks. These projects, found on the Coastal Adaptation site, will allow managers to better understand that vulnerability and improve the park's pre-hazard preparedness and post-hazard response.
Currents are necessary to move water, sediment, and nutrients near the coast but are potentially dangerous to swimmers. Dangerous currents occur along the Atlantic, Pacific, Arctic, and Gulf of Mexico coasts of the United States, as well as along the shores of the Great Lakes. Some dangerous currents present in parks include rip currents, structural currents, outlet currents, longshore currents, and channel currents.
Ranging from small scale block fall to immense landslides, these processes shape coastal landscapes. Waves, currents, and storm surges coupled with sea level rise act to modify sediment supply along our parks’ coasts. Over time, these processes may steepen adjacent and unconsolidated shores leading to bluff retreat and landslides.
Nuisance flooding is recurrent shallow flooding that occurs during unusually high, high tide events. It is particularly likely in areas with flat topography where local elevation is near that of the high tide line. Nuisance flooding causes public inconvenience and is expected to increase with sea level rise.
Seiches are a stationary, oscillating, wave in lake or semi-enclosed basin. Like water sloshing back and forth in a bathtub, seiches contribute to shoreline erosion and have the potential to flood adjacent coast. This phenomena is usually caused by strong winds and rapid changes in atmospheric pressure which pile up water on one end of a basin.
Coastal Storms are the primary drivers of coastal change. During the passage of major storms, strong winds, heavy rains, large waves, and storm surges frequently impact coastal parks. Although necessary, storms alter coastal landforms such as barrier islands and place many park structures at risk.
Sites:Geologic Resources Division, Fort Matanzas National Monument, Golden Gate National Recreation Area, Gulf Islands National Seashore
Storm surge may severely impact coastal geomorphology and inundate park resources. Brought by coastal storms, storm surge can be dangerous and have lasting effects. Coastal areas that remain at low elevation are prone to the effects of storm surge. The magnitude of a storm surge is increased when coupled with sea level rise.
Generated by any large displacement of the sea surface, tsunami waves can travel at speeds in excess of 500 mph (805 km/h) and can rush upward hundreds of feet in elevation upon landfall. These large waves can severely alter the coastal landscape through rapid erosion and deposition of sediment. Powerful wave action may transport coastal vegetation and marine debris as well as flood and damage park structures.
