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Research about Republic of the Marshall Islands

Source-linked reports with geographic coverage including Republic of the Marshall Islands.

15 recordsLinked to original sources
USGS2023

Developing satellite-estimated precipitation monthly reports for selected locations in the Republic of the Marshall Islands

The Republic of the Marshall Islands (also known as the Marshall Islands) is a nation of more than 30 low-lying atolls and islands, most of which are inhabited, dispersed across an Exclusive Economic Zone over 770,000 square miles in the tropical central north Pacific Ocean. Monitoring environmental conditions for potential drought risk is challenging in such a dispersed island nation, and current drought hazard products provide generalities regarding conditions on a broad geographic scale. U.S. Geological Survey scientists and managers of natural resources and natural hazards in the Marshall Islands used Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (called “IMERG”) satellite estimates of precipitation to develop content and a template for timely monthly reporting of precipitation for 23 inhabited atolls and islands. The IMERG data are available in a U.S. Geological Survey data release at https://doi.org/10.5066/P95ANG3N . The monthly reports itself are available in a U.S. Geological Survey data release at https://doi.org/10.5066/P90J1426 . This Data Report describes the collaboration process and results of developing the report content and layout.

Data Report↗
USGS2020

Inundation exposure assessment for Majuro Atoll, Republic of the Marshall Islands using a high-accuracy digital elevation model

Majuro Atoll in the central Pacific has high coastal vulnerability due to low-lying islands, rising sea level, high wave events, eroding shorelines, a dense population center, and limited freshwater resources. Land elevation is the primary geophysical variable that determines exposure to inundation in coastal settings. Accordingly, coastal elevation data (with accuracy information) are critical for assessments of inundation exposure. Previous research has demonstrated the importance of using high-accuracy elevation data and rigorously accounting for uncertainty in inundation assessments. A quantitative analysis of inundation exposure was conducted for Majuro Atoll, including accounting for the cumulative vertical uncertainty from the input digital elevation model (DEM) and datum transformation. The project employed a recently produced and validated DEM derived from structure-from-motion processing of very-high-resolution aerial imagery. Areas subject to marine inundation (direct hydrologic connection to the ocean) and low-lying lands (disconnected hydrologically from the ocean) were mapped and characterized for three inundation levels using deterministic and probabilistic methods. At the highest water level modeled (3.75 ft, or 1.143 m), more than 34% of the atoll study area is likely to be exposed to inundation (68% chance or greater), while more than 20% of the atoll is extremely likely to be exposed (95% chance or greater). The study demonstrates the substantial value of a high-accuracy DEM for assessing inundation exposure of low-relief islands and the enhanced information from accounting for vertical uncertainty.

Majuro Atoll↗
USGS2020

The importance of explicitly modelling sea-swell waves for runup on reef-lined coasts

The importance of explicitly modelling sea-swell waves for runup was examined using a 2D XBeach short wave-averaged (surfbeat, “XB-SB”) and a wave-resolving (non-hydrostatic, “XB-NH”) model of Roi-Namur Island on Kwajalein Atoll in the Republic of Marshall Islands. Field observations on water levels, wave heights, and wave runup were used to drive and evaluate both models, which were subsequently used to determine the effect of sea-level rise and extreme wave conditions on wave runup and its components. Results show that specifically modelling the sea-swell component (using XB-NH) provides a better approximation of the observed runup than XB-SB (which only models the time-variation of the sea-swell wave height), despite good model performance of both models on reef flat water levels and wave heights. XB-SB has a bias of −0.108 – 0.057 m and scatter index of 0.083–0.639, whereas XB-NH has bias of −0.132 – 0.055 m and 0.122–0.490, respectively. However, both models under-predict runup peaks. The difference between XB-SB and XB-NH increases for more extreme wave events and higher sea levels, as XB-NH resolves individual waves and therefore captures SS-wave motions in runup. However, for even larger forcing conditions with offshore wave heights of 6 m, the island is flooded in both XB-SB and XB-NH computations, regardless the sea-swell wave energy contribution. In such cases XB-SB would be adequate to model flooding depths and extents on the island while requiring 4–5 times less computational effort.

Roi-Namur Island↗
USGS2020

The impacts of a changing climate to DOD coastal facilities in the tropical Pacific Ocean

The USGS, the National Oceanic and Atmospheric Administration (NOAA), Deltares, and the University of Hawaii (UH) recently completed a study investigating the impact of a changing climate and sea-level rise on Roi-Namur Island on Kwajalein Atoll in the Republic of the Marshall Islands, which is part of the Ronald Reagan Ballistic Missile Defense Test Site (RTS). The isolated location of RTS makes it uniquely suited to support realistic testing of missiles and intercept scenarios with minimal safety and environmental concerns. In addition, this unique location supports research and development for space and missile programs and space reconnaissance and surveillance operations. RTS has been a critical component of the Pacific Range, with the world’s most advanced telemetry, optics, and radar instrumentation used to collect metric and signature data on missiles.

Kwajalein Atoll↗
USGS2018

Evaluating the potential for near-shore bathymetry on the Majuro Atoll, Republic of the Marshall Islands, using Landsat 8 and WorldView-3 imagery

Satellite-derived near-shore bathymetry (SDB) is becoming an increasingly important method for assessing vulnerability to climate change and natural hazards in low-lying atolls of the northern tropical Pacific Ocean. Satellite imagery has become a cost-effective means for mapping near-shore bathymetry because ships cannot collect soundings safely while operating close to the shore. Also, green laser light detection and ranging (lidar) acquisitions are expensive in remote locations. Previous research has demonstrated that spectral band ratio-based techniques, commonly called the natural logarithm approach, may lead to more precise measurements and modeling of bathymetry because of the phenomenon that different substrates at the same depth have approximately equal ratio values. The goal of this research was to apply the band ratio technique to Landsat 8 at-sensor radiance imagery and WorldView-3 atmospherically corrected imagery in the coastal waters surrounding the Majuro Atoll, Republic of the Marshall Islands, to derive near-shore bathymetry that could be incorporated into a seamless topobathymetric digital elevation model of Majuro. Attenuation of light within the water column was characterized by measuring at-sensor radiance and reflectance at different depths and calculating an attenuation coefficient. Bathymetric lidar data, collected by the U.S. Naval Oceanographic Office in 2006, were used to calibrate the SDB results. The bathymetric lidar yielded a strong linear relation with water depths. The Landsat 8-derived SDB estimates derived from the blue/green band ratio exhibited a water attenuation extinction depth of 6 meters with a coefficient of determination R 2 =0.9324. Estimates derived from the coastal/red band ratio had an R 2 =0.9597. At the same extinction depth, SDB estimates derived from WorldView-3 imagery exhibited an R 2 =0.9574. Because highly dynamic coastal shorelines can be affected by erosion, wetland loss, hurricanes, sea-level rise, urban development, and population growth, consistent bathymetric data are needed to better understand sensitive coastal land/water interfaces in areas subject to coastal disasters.

Majuro Atoll↗
USGS2018

One-meter topobathymetric digital elevation model for Majuro Atoll, Republic of the Marshall Islands, 1944 to 2016

Atoll and island coastal communities are highly exposed to sea-level rise, tsunamis, storm surges, rogue waves, king tides, and the occasional combination of multiple factors, such as high regional sea levels, extreme high local tides, and unusually strong wave set-up. The elevation of most of these atolls averages just under 3 meters (m), with many areas roughly at sea level. The lack of high-resolution topographic data has been identified as a critical data gap for hazard vulnerability and adaptation efforts and for high-resolution inundation modeling for atoll nations. Modern topographic survey equipment and airborne lidar surveys can be very difficult and costly to deploy. Therefore, unmanned aircraft systems (UAS) were investigated for collecting overlapping imagery to generate topographic digital elevation models (DEMs). Medium- and high-resolution satellite imagery (Landsat 8 and WorldView-3) was investigated to derive nearshore bathymetry. The Republic of the Marshall Islands is associated with the United States through a Compact of Free Association, and Majuro Atoll is home to the capital city of Majuro and the largest population of the Republic of the Marshall Islands. The only elevation datasets currently available for the entire Majuro Atoll are the Shuttle Radar Topography Mission and the Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model Version 2 elevation data, which have a 30-m grid-cell spacing and a 8-m vertical root mean square error (RMSE). Both these datasets have inadequate spatial resolution and vertical accuracy for inundation modeling. The final topobathymetric DEM (TBDEM) developed for Majuro Atoll is derived from various data sources including charts, soundings, acoustic sonar, and UAS and satellite imagery spanning over 70 years of data collection (1944 to 2016) on different sections of the atoll. The RMSE of the TBDEM over the land area is 0.197 m using over 70,000 Global Navigation Satellite System real-time kinematic survey points for validation, and 1.066 m for Landsat 8 and 1.112 m for WorldView-3 derived bathymetry using over 16,000 and 9,000 lidar bathymetry points, respectively.

Majuro Atoll↗
USGS2017

Land-use change and managed aquifer recharge effects on the hydrogeochemistry of two contrasting atoll island aquifers, Roi-Namur Island, Republic of the Marshall Islands

Freshwater resources on low-lying atoll islands are highly vulnerable to climate change and sea-level rise. In addition to rainwater catchment, groundwater in the freshwater lens is a critically important water resource on many atoll islands, especially during drought. Although many atolls have high annual rainfall rates, dense natural vegetation and high evapotranspiration rates can limit recharge to the freshwater lens. Here we evaluate the effects of land-use/land-cover change and managed aquifer recharge on the hydrogeochemistry and supply of groundwater on Roi-Namur Island, Republic of the Marshall Islands. Roi-Namur is an artificially conjoined island that has similar hydrogeology on the Roi and Namur lobes, but has contrasting land-use/land-cover and managed aquifer recharge only on Roi. Vegetation removal and managed aquifer recharge operations have resulted in an estimated 8.6 x 105 m3 of potable groundwater in the freshwater lens on Roi, compared to only 1.6 x 104 m3 on Namur. We use groundwater samples from a suite of 33 vertically nested monitoring wells, statistical testing, and geochemical modeling using PHREEQC to show that the differences in land-use/land-cover and managed aquifer recharge on Roi and Namur have a statistically significant effect on several groundwater-quality parameters and the controlling geochemical processes. Results also indicate a seven-fold reduction in the dissolution of carbonate rock in the freshwater lens and overlying vadose zone of Roi compared to Namur. Mixing of seawater and the freshwater lens is a more dominant hydrogeochemical process on Roi because of the greater recharge and flushing of the aquifer with freshwater as compared to Namur. In contrast, equilibrium processes and dissolution-precipitation non-equilibrium reactions are more dominant on Namur because of the longer residence times relative to the rate of geochemical reactions. Findings from Roi-Namur Island support selective land-use/land-cover change and managed aquifer recharge as a promising management approach for communities on other low-lying atoll islands to increase the resilience of their groundwater supplies and help them adapt to future climate change related stresses.

Roi-Namur↗
USGS2016

Identification and classification of very low frequency waves on a coral reef flat

Very low frequency (VLF, 0.001–0.005 Hz) waves are important drivers of flooding of low-lying coral reef-islands. In particular, VLF wave resonance is known to drive large wave runup and subsequent overwash. Using a 5 month data set of water levels and waves collected along a cross-reef transect on Roi-Namur Island in the Republic of the Marshall Islands, the observed VLF motions were categorized into four different classes: (1) resonant, (2) (nonresonant) standing, (3) progressive-growing, and (4) progressive-dissipative waves. Each VLF class is set by the reef flat water depth and, in the case of resonance, the incident-band offshore wave period. Using an improved method to identify VLF wave resonance, we find that VLF wave resonance caused prolonged (∼0.5–6.0 h), large-amplitude water surface oscillations at the inner reef flat ranging in wave height from 0.14 to 0.83 m. It was induced by relatively long-period, grouped, incident-band waves, and occurred under both storm and nonstorm conditions. Moreover, observed resonant VLF waves had nonlinear, bore-like wave shapes, which likely have a larger impact on the shoreline than regular, sinusoidal waveforms. As an alternative technique to the commonly used Fast Fourier Transformation, we propose the Hilbert-Huang Transformation that is more computationally expensive but can capture the wave shape more accurately. This research demonstrates that understanding VLF waves on reef flats is important for evaluating coastal flooding hazards.

Roi-Namur Island↗
USGS2015

The influence of coral reefs and climate change on wave-driven flooding of tropical coastlines

A numerical model, XBeach, calibrated and validated on field data collected at Roi-Namur Island on Kwajalein Atoll in the Republic of Marshall Islands, was used to examine the effects of different coral reef characteristics on potential coastal hazards caused by wave-driven flooding and how these effects may be altered by projected climate change. The results presented herein suggest that coasts fronted by relatively narrow reefs with steep fore reef slopes (~1:10 and steeper) and deeper, smoother reef flats are expected to experience the highest wave runup. Wave runup increases for higher water levels (sea level rise), higher waves, and lower bed roughness (coral degradation), which are all expected effects of climate change. Rising sea levels and climate change will therefore have a significant negative impact on the ability of coral reefs to mitigate the effects of coastal hazards in the future.

Geophysical Research Letters↗
USGS2008

Ground water on tropical Pacific Islands— Understanding a vital resource

To a casual observer, tropical Pacific islands seem idyllic. Closer scrutiny reveals that their generally small size makes them particularly vulnerable to economic and environmental stresses imposed by rapidly growing populations, increasing economic development, and global climate change. On these islands, freshwater is one of the most precious resources. Ground water is the main source of drinking water on many islands, and for quite a few islands, it is the only reliable source of water throughout the year. Faced with a growing demand for this valuable resource, and the potential negative effects on its availability and quality from changes in global climate, increasingly sophisticated management approaches will be needed to ensure a dependable supply of freshwater for the residents of these islands. Much scientific information has been collected by the U.S. Geological Survey (USGS) and other organizations about the ground-water resources of tropical Pacific islands. The aim of this Circular is to give members of the public, policymakers, and other stakeholders knowledge that will help ensure that this information can be used to make informed decisions about the management of these life-giving resources. As the demand for freshwater grows, new monitoring and research efforts will be needed to (1) characterize the extent and sustainability of ground-water resources on different tropical Pacific islands, (2) better understand linkages between ground-water discharge and freshwater and nearshore ecosystems, and (3) prepare for the effects of climate change, which will likely include the loss of habitable land and reduced areas for the accumulation of ground water as a result of rising sea levels.

Laura area of Majuro Atoll↗
USGS1997

Ground-water geochemistry of Kwajalein Island, Republic of the Marshall Islands, 1991

Ground water on Kwajalein Island is an important source of drinking water, particularly during periods of low rainfall. Fresh ground water is found as a thin lens underlain by saltwater. The concentration of dissolved ions increases with depth below the water table and proximity to the shoreline as high-salinity seawater mixes with fresh ground water. The maximum depth of the freshwater lens is 37 ft. Chloride is assumed to be non-reactive under the range of geochemical conditions on the atoll. The concentration of chloride thus is used as a conservative constituent to evaluate freshwater-saltwater mixing within the aquifer. Concentrations of sodium and for the most part, potassium and sulfate, also appear to be determined by conservative mixing between saltwater and rain. Concentrations of calcium, magnesium, and strontium are higher than expected from conservative mixing; these higher concentrations are a result of the dissolution of carbonate minerals. An excess in dissolved inorganic carbon results from carbonate-mineral dissolution and from the oxidation of organic matter in the aquifer; the stoichiometric difference between excess dissolved inorganic carbon and excess bivalent cations is used as a measure of the amount of organic-matter oxidation. Organic-matter oxidation also is indicated by the low concentration of dissolved oxygen, high concentrations of nutrients, and the presence of hydrogen sulfide in many of the water samples. Low levels of dissolved oxygen indicate oxic respiration, and sulfate reduction is indicated by hydrogen sulfide. The amount of dissolved inorganic carbon released during organic-matter oxidation is nearly equivalent to the amount of carbonate-mineral dissolution. Organic-matter oxidation and carbonate-mineral dissolution seem to be most active either in the unsaturated zone or near the top of the water table. The most plausible explanation is that high amounts of oxic respiration in the unsaturated zone generate carbon dioxide, which causes carbonate minerals to dissolve. Ground water contaminated by petroleum hydrocarbons had the highest levels of mineral dissolution and organic respiration (including sulfate reduction), indicating that bacteria are oxidizing the contaminants.

Kwajalein Island↗
USGS1987

Ground-water resources of the Laura area, Majuro Atoll, Marshall Islands

The water system that supplies the heavily populated Dalap-Uliga-Darrit (DUD) area of Majuro atoll, Marshall Island, relies almost entirely upon airstrip catchment of rain water. Droughts cause severe water supply problems and water rationing is required, even during periods of normal rainfall. The Laura area contains a substantial lens of fresh groundwater that could be developed for export to the DUD area 30 mi to the east. Study of the groundwater resource at Laura involved a survey of existing wells, installation of monitoring wells and test holes, compilation of continuous records of rainfall and water level fluctuations, and collection of water quality data. Test hole data permitted the definition of three geohydrologic units which correlate well with similar units in Bikini and Enewetak atolls. The units consist of two layers of unconsolidated reef and lagoon sediments resting on a dense, highly permeable limestone. The potable water zone, or freshwater nucleus, of the lens is contained mostly within the unconsolidated layers, which are much less permeable than the basal limestone. Recharge to the Laura freshwater lens is estimated to be 1.8 mil gal/day, based on an average annual rainfall of 140 in. Sustainable yield is estimated to be about 400,000 gal/day. Shallow skimming wells or infiltration galleries similar to those used on Kwajalein atoll would be appropriate to develop the freshwater lens. The impact of development on the lens can be determined by monitoring the salinity in developed water and in a network of monitor wells.

Laura area, Majuro Atoll↗
USGS1986

Pacific Enewetak Atoll Crater Exploration (PEACE) program, Enewetak Atoll, Republic of the Marshall Islands. Part 1: Drilling operations and descriptions of boreholes in vicinity of KOA and OAK craters

From mid-1984 through mid-1985, the United States Geological Survey (USGS) engaged in an investigation of two craters formed from high-yield, near-surface nuclear bursts in the Marshall Islands at Enewetak Atoll (figures 1 and 2). Supported by the Defense Nuclear Agency (DNA), this cooperative venture is referred to by the acronym PEACE, derived from its official name, Pacific Enewetak Atoll Crater Exploration Program. The craters studied, KOA and OAK, resulted from 1.4- and 8.9-megaton, near-surface bursts detonated near the northern perimeter of the Enewetak lagoon on May 12 and June 28, 1958, respectively. At that time, Enewetak was administered by the United States Government under the auspices of the Trust Territories of the Pacific Islands (TTPI) and formed a part of the Pacific Proving Grounds (PPG). OAK and KOA are among the only high-yield nuclear craters available for studies of cratering processes and crater-related effects.

Enewetak Atoll↗
USGS1966

Oxygen and carbon isotopic composition of limestones and dolomites, Bikini and Eniwetok atolls

Aragonitic, unconsolidated sediments from the borings on the Eniwetok and Bikini atolls are isotopically identical with unaltered skeletal fragments, whereas the recrystallized limestones exhibit isotopic variations resulting from alteration in meteoric waters during periods of emergence. Dolomites and associated calcites are enriched in O 18 , perhaps because of interaction with hypersaline brines.

Bikini Atoll, Eniwetok Atoll↗