The CMHRP studies the physical and geological processes that affect islands and their margins. The data that the CMHRP collects are used to document historical and contemporary baseline conditions on islands and to track the impact of short-term ocean events and longer-term sea level rise. This information feeds into forecasts of the islands' future vulnerabilities and provides support for management decisions about land use, ecosystems, water resources, and coastline protection. The different types of islands, their specific vulnerabilities, and the CMHRP's activities are described below.
BARRIER ISLANDS
Barrier islands (e.g., Outer Banks of North Carolina; Chandeleur Islands, Louisiana) are low-lying features located within a few kilometers of the mainland and are usually composed of erodable sediments. Barrier islands occur along open coasts on all U.S. margins that have adequate sediment sources. They are one of the most important categories of islands in the United States, both for the habitats they provide and the protection they afford for mainland coastlines and back-barrier lagoons. Many barrier islands have significant populations, especially in summertime, and they support sensitive ecosystems.
Barrier islands may migrate in response to sea level rise if there is sufficient sediment supply, or they may be drowned if local sea level rise is too rapid or extreme. The CMHRP studies the geologic history of barrier islands and tracks their response to recent sea level rise in order to forecast how changing sediment supply and expected rapid increases in sea level may affect their long-term viability. The CMHRP also measures changes to barrier islands and the surrounding seafloor in response to overwash, storm surge, and extreme events. Time series of photographs, lidar data, and shallow offshore seafloor mapping have permitted the CMHRP to quantify the impact of erosional events in settings as diverse as Fire Island (New York), the Chandeleur Islands (Louisiana), and Barter Island (U.S. Arctic).
ROCKY ISLANDS
Rocky islands (e.g., Channel Islands, California; Mount Desert Island, Maine; Whidbey Island, Washington) that are not directly associated with volcanoes typically are either slivers of rock that got caught up in tectonic plate boundary motions (e.g., Channel Islands) or masses of rock that became separated from the mainland by channel flooding as sea level rose at the end of the last major glaciation (e.g., Maine islands). While rocky islands as a whole are more resistant to erosion than sandy barrier islands, they remain vulnerable to coastal bluff retreat and beach erosion. In addition, towns on rocky islands typically concentrate near low-lying harbors where the effects of sea level rise and storm surge, as well as tsunamis, may be enhanced. Lack of freshwater can limit these islands' economic development and carrying capacity. Smaller rocky islands are often important seabird and seal habitats, keeping these animals out of the reach of predators while providing easy access to the surrounding ocean ecosystems. The CMHRP has conducted extensive benthic habitat and geologic studies of rocky islands in Puget Sound and offshore California.
VOLCANIC ISLANDS
Volcanic islands, not all of which still host active volcanoes, are found at mantle hotspots (e.g., Hawaiʻi , American Samoa) and near tectonic plate boundaries (e.g., Aleutian Islands, Marianas, Guam, Puerto Rico, Cuba, Iceland). On some volcanic islands, a thick layer of sediments has accumulated, altering the island's morphology, habitats and ecosystems, and freshwater resources, and making the island susceptible to erosion. The impact of sea level rise on volcanic islands and their communities is similar to that on rocky islands; however, volcanic islands are more susceptible to certain erosional and earthquake shaking hazards due to the properties of volcanic soils.
Many highly populated volcanic islands, such as those in the Caribbean Sea, lie near active plate boundaries that generate strong earthquakes. Both active-boundary islands and mid-plate volcanic islands such as Hawaiʻi , which are surrounded by thousands of kilometers of open ocean, are at risk from tsunamis. The CMHRP has collected a wide variety of geophysical and geological data offshore the volcanic islands of the Caribbean to study past, present, and future geohazard threats and has conducted similar studies in parts of the Aleutian Islands. The CMHRP has also tracked the recolonization of benthic habitats following Aleutian arc volcanic eruptions and carried out studies of coastal aquifers, contaminant transport, and fringing coral reefs in Hawaiʻi.
CORAL ISLANDS
Coral islands include both exposed, ancient coral reefs (e.g., Florida Keys) and atolls, which are submerged volcanic islands fringed or topped by thick coral reefs that form an emergent land mass. The Republic of the Marshall Islands and parts of Micronesia are examples of U.S.-affiliated Pacific islands where coral atolls occur. At their highest points, coral islands are elevated only a few meters above the surrounding ocean and are among the lands most threatened by rapid twenty-first century sea level rise as well as by routine high tides and storm events. Coral islands have limited freshwater resources and capacity for energy generation, and atolls located distant from major landmasses rely on the viability of ports and airport infrastructure to provide supplies and connections with the outside world.
In the Florida Keys, the CMHRP has mapped bedrock and benthic habitats in offshore coral reefs and studied reef morbidity related to climate change and other factors. In the Marshall Islands, the CMHRP is assessing the vulnerability of atolls to both short-term events, which are now causing annual flooding in its capital, Majuro, and longer-term change in sea level, which is currently increasing at up to 1 cm per year. The CMHRP also collects time series of ocean environmental parameters and conducts groundwater studies to track the quality and quantity of freshwater resources beneath a Marshall Islands atoll.
GLACIAL MORAINE ISLANDS
Glacial moraine islands are formed from sediments pushed ahead of ice sheets and that remained after the ice sheets retreated. Long Island, Block Island, Martha's Vineyard, and Nantucket together form the terminal moraine of an ice sheet that covered the northeastern United States about 21,000 years ago. Flaxman Island on the eastern U.S. Arctic coastline may be another moraine remnant. The relatively few glacial moraine islands have outsized importance due to their population and locations. Long Island is home to ~2% of the U.S. population and was severely damaged during Superstorm Sandy. The CMHRP has conducted exhaustive seafloor mapping and sediment transport studies around southern Long Island and in the waters surrounding Massachusetts. In addition, the CMHRP has formally assessed coastal vulnerabilities in this area and provided coastal zone managers and urban planners with the scientific information needed to make sound decisions about rebuilding infrastructure, restoring dunes and seawalls, and preventing catastrophic impacts from future storms.
ENGINEERED ISLANDS
Engineered islands are taking on increasing importance for land-starved coastal cities, various industries, ecosystem restoration, and international security. In the United States, Asia, the Middle East, Europe, and the western Pacific Ocean, coastal cities have built islands to support airports, living sites, recreation, industry, or energy/waste disposal infrastructure. At the edge of the Arctic Ocean off Prudhoe Bay, artificial islands such as Endicott and Northstar are used exclusively to extract oil from deep wells. An increasing concern for international security is engineered islands in disputed marine areas.
Engineered islands typically lie only a few meters above the high tide line and are vulnerable to the same catastrophic events and long-term sea level rise as barrier islands. Some of these islands are connected to the mainland and could be cut off by storm surges or tsunamis. In many cases, these islands host critical infrastructure, and a major ocean incursion could shut down a city's airport, electrical generating capacity, liquid natural gas storage facility, or sewage processing plant, and potentially lead to contamination of surrounding waters. The CMHRP has not previously conducted studies of the impact of engineered islands on sediment transport patterns, coastal habitats, and various geologic and physical processes, nor explicitly assessed the vulnerability of these islands to storms or sea level rise; however, the methodologies that the CMHRP has developed for barrier islands could be readily modified and applied to engineered islands.
FUTURE PLANS
The CMHRP anticipates expanded studies on the impact of locally variable sea level rise on natural islands, in particular, barrier, coral, and glacial moraine islands. The CMHRP will adopt a multifaceted approach that includes acquisition of baseline geologic and physical data across the land-ocean margin, characterization of subterranean freshwater resources, formal assessments of coastal vulnerability, and modeling to predict the impacts of short- and long-term climate change on islands. The CMHRP will also expand studies of geohazards related to islands, with an emphasis on tsunami hazards for the Caribbean, affiliated Pacific Island nations, Hawaiʻi, and the U.S. Pacific coast, and on the tsunami-generating potential of the Aleutian arc.
Explore the CMHRP Decadal Strategic Plan geonarrative
The CMHRP Decadal Science Strategy 2020-2030
This geonarrative constitutes the Decadal Science Strategy of the USGS's Coastal and Marine Hazards and Resources Program for 2020 to 2030.
Coastal System Change at Fire Island, New York
Barrier Island Evolution
The CMHRP studies the physical and geological processes that affect islands and their margins. The data that the CMHRP collects are used to document historical and contemporary baseline conditions on islands and to track the impact of short-term ocean events and longer-term sea level rise. This information feeds into forecasts of the islands' future vulnerabilities and provides support for management decisions about land use, ecosystems, water resources, and coastline protection. The different types of islands, their specific vulnerabilities, and the CMHRP's activities are described below.
BARRIER ISLANDS
Barrier islands (e.g., Outer Banks of North Carolina; Chandeleur Islands, Louisiana) are low-lying features located within a few kilometers of the mainland and are usually composed of erodable sediments. Barrier islands occur along open coasts on all U.S. margins that have adequate sediment sources. They are one of the most important categories of islands in the United States, both for the habitats they provide and the protection they afford for mainland coastlines and back-barrier lagoons. Many barrier islands have significant populations, especially in summertime, and they support sensitive ecosystems.
Barrier islands may migrate in response to sea level rise if there is sufficient sediment supply, or they may be drowned if local sea level rise is too rapid or extreme. The CMHRP studies the geologic history of barrier islands and tracks their response to recent sea level rise in order to forecast how changing sediment supply and expected rapid increases in sea level may affect their long-term viability. The CMHRP also measures changes to barrier islands and the surrounding seafloor in response to overwash, storm surge, and extreme events. Time series of photographs, lidar data, and shallow offshore seafloor mapping have permitted the CMHRP to quantify the impact of erosional events in settings as diverse as Fire Island (New York), the Chandeleur Islands (Louisiana), and Barter Island (U.S. Arctic).
ROCKY ISLANDS
Rocky islands (e.g., Channel Islands, California; Mount Desert Island, Maine; Whidbey Island, Washington) that are not directly associated with volcanoes typically are either slivers of rock that got caught up in tectonic plate boundary motions (e.g., Channel Islands) or masses of rock that became separated from the mainland by channel flooding as sea level rose at the end of the last major glaciation (e.g., Maine islands). While rocky islands as a whole are more resistant to erosion than sandy barrier islands, they remain vulnerable to coastal bluff retreat and beach erosion. In addition, towns on rocky islands typically concentrate near low-lying harbors where the effects of sea level rise and storm surge, as well as tsunamis, may be enhanced. Lack of freshwater can limit these islands' economic development and carrying capacity. Smaller rocky islands are often important seabird and seal habitats, keeping these animals out of the reach of predators while providing easy access to the surrounding ocean ecosystems. The CMHRP has conducted extensive benthic habitat and geologic studies of rocky islands in Puget Sound and offshore California.
VOLCANIC ISLANDS
Volcanic islands, not all of which still host active volcanoes, are found at mantle hotspots (e.g., Hawaiʻi , American Samoa) and near tectonic plate boundaries (e.g., Aleutian Islands, Marianas, Guam, Puerto Rico, Cuba, Iceland). On some volcanic islands, a thick layer of sediments has accumulated, altering the island's morphology, habitats and ecosystems, and freshwater resources, and making the island susceptible to erosion. The impact of sea level rise on volcanic islands and their communities is similar to that on rocky islands; however, volcanic islands are more susceptible to certain erosional and earthquake shaking hazards due to the properties of volcanic soils.
Many highly populated volcanic islands, such as those in the Caribbean Sea, lie near active plate boundaries that generate strong earthquakes. Both active-boundary islands and mid-plate volcanic islands such as Hawaiʻi , which are surrounded by thousands of kilometers of open ocean, are at risk from tsunamis. The CMHRP has collected a wide variety of geophysical and geological data offshore the volcanic islands of the Caribbean to study past, present, and future geohazard threats and has conducted similar studies in parts of the Aleutian Islands. The CMHRP has also tracked the recolonization of benthic habitats following Aleutian arc volcanic eruptions and carried out studies of coastal aquifers, contaminant transport, and fringing coral reefs in Hawaiʻi.
CORAL ISLANDS
Coral islands include both exposed, ancient coral reefs (e.g., Florida Keys) and atolls, which are submerged volcanic islands fringed or topped by thick coral reefs that form an emergent land mass. The Republic of the Marshall Islands and parts of Micronesia are examples of U.S.-affiliated Pacific islands where coral atolls occur. At their highest points, coral islands are elevated only a few meters above the surrounding ocean and are among the lands most threatened by rapid twenty-first century sea level rise as well as by routine high tides and storm events. Coral islands have limited freshwater resources and capacity for energy generation, and atolls located distant from major landmasses rely on the viability of ports and airport infrastructure to provide supplies and connections with the outside world.
In the Florida Keys, the CMHRP has mapped bedrock and benthic habitats in offshore coral reefs and studied reef morbidity related to climate change and other factors. In the Marshall Islands, the CMHRP is assessing the vulnerability of atolls to both short-term events, which are now causing annual flooding in its capital, Majuro, and longer-term change in sea level, which is currently increasing at up to 1 cm per year. The CMHRP also collects time series of ocean environmental parameters and conducts groundwater studies to track the quality and quantity of freshwater resources beneath a Marshall Islands atoll.
GLACIAL MORAINE ISLANDS
Glacial moraine islands are formed from sediments pushed ahead of ice sheets and that remained after the ice sheets retreated. Long Island, Block Island, Martha's Vineyard, and Nantucket together form the terminal moraine of an ice sheet that covered the northeastern United States about 21,000 years ago. Flaxman Island on the eastern U.S. Arctic coastline may be another moraine remnant. The relatively few glacial moraine islands have outsized importance due to their population and locations. Long Island is home to ~2% of the U.S. population and was severely damaged during Superstorm Sandy. The CMHRP has conducted exhaustive seafloor mapping and sediment transport studies around southern Long Island and in the waters surrounding Massachusetts. In addition, the CMHRP has formally assessed coastal vulnerabilities in this area and provided coastal zone managers and urban planners with the scientific information needed to make sound decisions about rebuilding infrastructure, restoring dunes and seawalls, and preventing catastrophic impacts from future storms.
ENGINEERED ISLANDS
Engineered islands are taking on increasing importance for land-starved coastal cities, various industries, ecosystem restoration, and international security. In the United States, Asia, the Middle East, Europe, and the western Pacific Ocean, coastal cities have built islands to support airports, living sites, recreation, industry, or energy/waste disposal infrastructure. At the edge of the Arctic Ocean off Prudhoe Bay, artificial islands such as Endicott and Northstar are used exclusively to extract oil from deep wells. An increasing concern for international security is engineered islands in disputed marine areas.
Engineered islands typically lie only a few meters above the high tide line and are vulnerable to the same catastrophic events and long-term sea level rise as barrier islands. Some of these islands are connected to the mainland and could be cut off by storm surges or tsunamis. In many cases, these islands host critical infrastructure, and a major ocean incursion could shut down a city's airport, electrical generating capacity, liquid natural gas storage facility, or sewage processing plant, and potentially lead to contamination of surrounding waters. The CMHRP has not previously conducted studies of the impact of engineered islands on sediment transport patterns, coastal habitats, and various geologic and physical processes, nor explicitly assessed the vulnerability of these islands to storms or sea level rise; however, the methodologies that the CMHRP has developed for barrier islands could be readily modified and applied to engineered islands.
FUTURE PLANS
The CMHRP anticipates expanded studies on the impact of locally variable sea level rise on natural islands, in particular, barrier, coral, and glacial moraine islands. The CMHRP will adopt a multifaceted approach that includes acquisition of baseline geologic and physical data across the land-ocean margin, characterization of subterranean freshwater resources, formal assessments of coastal vulnerability, and modeling to predict the impacts of short- and long-term climate change on islands. The CMHRP will also expand studies of geohazards related to islands, with an emphasis on tsunami hazards for the Caribbean, affiliated Pacific Island nations, Hawaiʻi, and the U.S. Pacific coast, and on the tsunami-generating potential of the Aleutian arc.
Explore the CMHRP Decadal Strategic Plan geonarrative
The CMHRP Decadal Science Strategy 2020-2030
This geonarrative constitutes the Decadal Science Strategy of the USGS's Coastal and Marine Hazards and Resources Program for 2020 to 2030.