INSIGHTi
Tsunamis: Background and Introduction to
Detection, Forecasts, and Warnings
February 4, 2022
Background
Tsunamis are a series of extremely long waves caused by a large and sudden displacement of water in a
large waterbody, such as the ocean or an inland sea. That displacement can be caused by underwater
earthquakes, landslides, or volcanic eruptions, certain types of weather, and impacts from celestial objects
such as asteroids. Most tsunamis are the direct result of earthquakes or of landslides caused by
earthquakes. Tsunamis radiate from the point of initial displacement and move across the waterbody.
When tsunamis reach a coastline, they grow in wave height due to the shallowing waters, sometimes
causing coastal and inland flooding, destruction of infrastructure, injuries, and fatalities. Certain coastal
locations are especially vulnerable to tsunamis due to their proximity to tsunami sources, the depth and
characteristics of the waterbody bottom, and the topography and elevation of land near the coast. Large
displacements may cause tsunami impacts around the world; for example, the January 15, 2022,
underwater volcanic eruption in Tonga, a Pacific Island country, triggered a risk of tsunami impacts along
parts of coastlines in U.S. Pacific territories, Hawaii, and the West Coast, among locations in other
countries.
Detection, Forecasting, and Warnings
Congress has directed the National Oceanic and Atmospheric Administration (NOAA) to establish and
operate a Tsunami Program focused on detection, forecasting, warnings, research, notification, outreach,
and mitigation, as well as data collection and archiving, in consultation with federal and nonfederal
partners (33 U.S.C. §§3201-3208). Among other responsibilities, Congress instructed NOAA’s National
Weather Service, in conjunction with other NOAA line offices, to administer the program and provide
tsunami detection, forecasting, and warnings for the Pacific, Arctic, and Atlantic Ocean regions, including
the Caribbean Sea and the Gulf of Mexico. To do so, the Tsunami Program maintains marine
instrumentation, such as Deep-Ocean Assessment and Reporting of Tsunami (DART) buoys, two warning
centers, and a tsunami warning system. It also supports other tsunami-related activities at NOAA and its
partners.
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Instrumentation
NOAA depends on earth observing networks on land and in the ocean to collect information about water
levels and seismic activity. NOAA owns, operates, and maintains 40 DART systems located in the Pacific,
Atlantic, and Caribbean basins (Figure 1) that measure and transmit water level changes via seafloor
pressure recorders and moored surface buoys (Figure 2). International partners maintain additional DART
systems and share the collected information with NOAA. DART systems, along with tsunami capable tide
stations, provide direct measurements to support coastal threat evaluation and forecasting. NOAA uses
these data after an event to improve tsunami forecast modeling and coastal hazard assessments. NOAA
uses seismic and other data collected by the U.S. Geological Survey (USGS) and other countries to track
tsunami sources, such as earthquakes, volcanic eruptions, and landslides, to determine if they might
generate a damaging tsunami.
Figure 1. NOAA DART Station Locations
As of February 2, 2022
Source: NOAA, National Data Buoy Center, “Interactive Maps-DART.”
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Figure 2. DART Station Schematic
Source: NOAA, National Weather Service, “Deep-ocean Assessment and Reporting of Tsunami.”
Warning Centers
NWS operates two tsunami warning centers (TWCs): the National Tsunami Warning Center (NTWC) in
Alaska, which serves the continental United States (including Alaska) and Canada, and the Pacific
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Tsunami Warning Center (PTWC) in Hawaii, which serves Hawaii, the U.S. Pacific and Caribbean
territories, and the British Virgin Islands. PTWC acts as the primary forecast center for several
international and national warning systems. If instrumentation detects a tsunami, NOAA uses the
collected data to estimate potential impacts and amends forecasts with historical and event-specific data,
as available. The forecasts are then shared with emergency managers, the public, and other partners to
warn about the potential for a tsunami.
Tsunami Warnings
TWCs may issue several types of tsunami alerts, including information statements, watches, advisories,
and warnings. Alerts may be updated as information becomes available. The public may become aware of
an incoming tsunami in two main ways. The first is via official tsunami alerts broadcast through local
radio and television stations, wireless emergency alerts, NOAA weather radio, NOAA websites, or
outdoor sirens. Each type of alert provides information, including an estimate of the tsunami’s arrival
time, if applicable, potential impacts, and recommended actions to take, such as staying out of the water
or moving to higher ground. The second is by experiencing ground shaking from the tsunami source
itself, such as an earthquake, or noting changes in local coastal conditions. Some coastal populations near
the tsunami source may not have enough time to receive tsunami alerts prior to the arrival of a tsunami.
Other NOAA Tsunami Program Activities
NOAA supports other activities under its Tsunami Program, in addition to detection, forecasting, and
warning. Congress directed NOAA, in consultation with federal and nonfederal partners, to maintain a
tsunami research program (33 U.S.C §3205). The program focuses on improving tsunami measurement
technology and monitoring networks; models for increased speed and accuracy of forecasts and warnings;
and methods for predicting tsunami impacts on coastal communities and infrastructure. Congress also
authorized a national tsunami hazard mitigation program led by NOAA in coordination with the Federal
Emergency Management Agency, the USGS, and 28 states and territories (33 U.S.C. §3204). The
mitigation program aims to reduce tsunami impacts through collaboration, coordination, and financial and
technical support to partner states, such as through the support of nonfederal preparedness measures (e.g.,
the TsunamiReady program). Other parts of NOAA’s Tsunami Program focus on historical tsunami data
collection and archiving. Congress also has directed NOAA to provide technical assistance, operational
support, and training to support a global tsunami warning and mitigation network (33 U.S.C. §3206), in
addition to its responsibilities for U.S. states and territories.
Author Information
Eva Lipiec
Analyst in Natural Resources Policy
Disclaimer
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