Geology topics

Research about Hawaii

Source-linked reports with geographic coverage including Hawaii.

At least 253 records · Page 14Linked to original sources

USGS2022

Hawaiian forest bird conservation strategies for minimizing the risk of extinction: biological and biocultural considerations

The iconic forest birds of Hawai‘i are facing a conservation crisis. Across the Hawaiian Islands, native forest birds have been experiencing population declines that have accelerated in the last one to two decades. While habitat loss, invasive species, and non-native predators have negatively affected forest bird species for hundreds of years, and continue to do so, introduced diseases, particularly avian malaria, are the greatest threat to forest birds today. Further, climate change has increased temperatures in the high-elevation forests, facilitating the spread of disease into areas that were once largely disease-free. Rapid population declines have now (2022) pushed four Hawaiian honeycreeper species to the brink of extinction: the endangered ‘akikiki ( Oreomystis bairdi ) and ‘akeke‘e ( Loxops caeruleirostris ) on Kaua‘i Island, and kiwikiu ( Pseudonestor xanthophrys ) and ‘ākohekohe ( Palmeria dolei ) on Maui Island. The biologists that study these birds strongly agree that without a rapid conservation response to the threat of increasing disease mortality there is a high probability these species will go extinct in the coming decade. To help evaluate alternative conservation strategies for minimizing the risk of extinction, we convened diverse groups of experts with broad experience in Hawai‘i forest birds and ecosystems, as well as the management approaches being considered, to assess the probability of success of alternative management actions. In addition to assessing this crisis from a biological perspective, we convened a group of Native Hawaiian participants that have a strong connection to the forest birds, forests, and the integration of their culture in natural and biocultural resource management. They give voice to the significance of forest birds to Native Hawaiians and provide their perspectives on alternative management actions. Broadly, the three alternative management actions being considered to prevent the extinction of forest birds from the increasing threat of disease are (1) landscape-level mosquito control through the Wolbachia incompatible insect technique, (2) captive care, and (3) conservation translocations. The two key components of the problem of preventing extinction in these four bird species is time and risk. For each species, very few individuals remain, and they are all in danger of imminent extinction. Each management action takes time to implement, which might exceed the actual time to extinction. Additionally, each of these conservation actions has potential benefits and inherent risks, as well as substantial uncertainty in terms of being successful. Native Hawaiian perspectives and considerations also vary across the conservation actions. The expert evaluations summarized in this report provide a broad assessment of conservation strategies that could be undertaken to prevent the extinction of ‘akikiki, ‘akeke‘e, kiwikiu, and ‘ākohekohe. While this report does not recommend specific actions, the information is intended to support decision-makers as they assess which, if any, conservation strategies to pursue.

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USGS2022

Forest bird populations at the Big Island National Wildlife Refuge Complex, Hawai‘i

Endemic Hawaiian forest birds have experienced dramatic population declines. The Big Island National Wildlife Refuge Complex (BINWRC) was created for conservation of endangered Hawaiian forest birds and their habitats. Surveys have been conducted at two units of BINWRC to monitor forest bird populations and their response to management actions. We analyzed survey data from 1987 to 2019 at the Hakalau Forest Unit (HFU) and from 1995 to 2019 at the Kona Forest Unit (KFU). We analyzed three strata at HFU: open-forest, closed-forest, and pasture, and two strata at the KFU: upper (>1524 m elevation) and lower (<1524 m). In all years, ‘i‘iwi (Drepanis coccinea), ‘apapane (Himatione sanguinea), and Hawai‘i ‘amakihi (Chlorodrepanis virens virens) were the most abundant species at HFU. The three endangered forest bird species, Hawai‘i ‘ākepa (Loxops coccineus), ‘alawī (Loxops mana, also known as Hawai‘i creeper) and ‘akiapōlā‘au (Hemignathus wilsoni), had much lower densities. The most abundant species at KFU was ‘apapane, followed by Hawai‘i ‘amakihi and warbling white-eye (Zosterops japonicus) at much lower densities. At HFU we found a continuation of several trends observed in previous analyses from 1987–2012, with most species’ trends upward in pasture stratum, stable in the open-forest stratum, and downward in the closed-forest stratum. However, when we looked at the most recent decade at HFU, more species were showing downward trends in all three strata. At KFU results were mixed, with more species’ trends downward in the upper stratum and more species’ trends upward in the lower stratum. Populations of endangered forest species were either locally extirpated at KFU or in numbers too low to reliably estimate population densities. Both units in the BINWRC are important for conservation of forest birds on Hawai‘i Island, and our results show that HFU supports the majority of the three endangered forest bird species found on Hawai‘i Island. Our analysis also shows the importance of continuous monitoring and timely analysis to track forest bird populations. With the additional data provided by continued surveys, we determined conclusive population trends for species whose trends were previously inconclusive. Knowing current population densities, abundances, and trends allows managers to evaluate and adapt management actions to support forest bird conservation at the BINWRC.

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USGS2022

Host plant associations of Lepidoptera and implications for forest bird management at Hakalau Forest National Wildlife Refuge

Forests dominated or co-dominated by ‘ōhi‘a ( Metrosideros polymorpha ) are critical to most Hawaiian forest birds, but fungal diseases causing Rapid ‘Ōhi‘a Death (ROD) threaten ‘ōhi‘a-based food webs that support native bird communities on Hawai‘i Island. Caterpillars are the most frequently consumed arthropod prey of native birds and their young and are especially frequent in the diets of one threatened (T) and three endangered (E) species (“listed” species) at Hakalau Forest National Wildlife Refuge (Hakalau): ‘akiapōlā‘au ( Hemignathus wilsoni , E), ‘alawī (Hawai‘i creeper; Loxops mana , E), Hawai‘i ‘ākepa ( L. coccineus , E), and ‘i‘iwi ( Drepanis coccinea , T). Hakalau harbors the largest and most stable populations of listed forest birds in Hawai‘i, presumably due to the availability of food resources and the extent of suitable, managed habitat above the range of mosquito-borne avian malaria. Because a previous study indicated that only a few caterpillar species were important in the diets of listed birds at Hakalau, we investigated the distribution of caterpillars on common host plants available to foraging birds. Eleven native plant species hosted two or more taxa identified to genus or species, with at least seven from ‘ōhi‘a, six from koa ( Acacia koa ), and five from ‘ākala ( Rubus hawaiensis ). We identified 16 taxa to genus or species from 9 families, assigning 11 to species. Leaves, which were the focus of our sampling effort, were the substrate used by 20 caterpillar taxa, and dead wood or bark was used by 7 taxa. In a previous study, we classified 19 morphotypes of caterpillar mandibles in the diets of native and alien birds at Hakalau, and in the present study we dissected mandibles from caterpillars that likely matched 10 of those morphotypes. These 10 morphotypes potentially represented >95% of caterpillar prey found in the earlier diet study and were collected from 11 host plant species, with ‘ōhi‘a hosting 8 morphotypes, 4 of which were exclusive to ‘ōhi‘a. The most widely hosted morphotype was found on all 11 plant species that we sampled, including ‘ōhi‘a, but the other 9 morphotypes were found on 1–7 hosts. As shown by the previous diet study, each of the listed bird species consumed caterpillar prey consisting mostly of combinations of two morphotypes drawn from a pool of only five, indicating a high degree of specialization. In the present study, we collected three of the five key morphotypes only on ‘ōhi‘a, highlighting the importance of this tree to listed bird species. Because ‘ōhi‘a forests in Hakalau remain vulnerable to ROD, measures to mitigate the impacts of reduced ‘ōhi‘a cover are important to consider from the perspective of forest bird food webs and diet. Ongoing reforestation of former pasturelands with koa and common understory species should provide alternative caterpillar prey for forest birds. Our results and information from the literature indicate that koa supports, to varying degrees, nearly all forest birds at Hakalau, while ‘ākala, ‘ōhelo ( Vaccinium calycinum ), kōlea ( Myrsine lessertiana ), ‘ōlapa ( Cheirodendron trigynum ), pūkiawe ( Leptecophylla tameiameiae ), and māmaki ( Pipturus albidus ) could benefit bird populations by increasing prey availability and structural complexity in koa-dominated stands. Foraging studies and additional research to identify species and host plant associations of important forest bird prey, including caterpillars and other arthropods, can help managers evaluate the complex interactions between native forest birds and their food webs and habitats.

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USGS2022

Estimating soil moisture, actual evapotranspiration, climatic water deficit, and groundwater recharge during periods of drought for current and future climate conditions in Hawaiʻi

Mid- and end-of-century climate projections for the Hawaiian Islands indicate that rainfall is projected to decrease across large areas. In areas affected by drought or where the future climate becomes drier, reduced groundwater recharge can affect freshwater availability. Reduced rainfall can also reduce soil moisture, which can increase the risk of wildfire. Cloud-water interception, or fog drip, is the process by which cloud-water droplets are captured on the leaves and branches of plants with some of the captured cloud water subsequently dripping to the ground. Studies in Hawaiʻi indicate that fog drip can contribute substantially to total precipitation and may have the potential to lessen the negative effects of drought or a drying climate on freshwater availability and wildfire risk. Wildfire danger assessments in the continental United States have used estimates of soil moisture, evapotranspiration, and climatic water deficit (that is, the evaporative demand that exceeds available water) to improve the identification of areas at risk for wildfires. In this study, water-budget models developed for the islands of Kauaʻi, Oʻahu, Molokaʻi, Maui, and Hawaiʻi were used to quantify the effects of severe drought, future climate conditions, and reducing or eliminating fog drip on groundwater recharge, soil moisture, evapotranspiration, and climatic water deficit. Island-wide summaries of groundwater recharge, soil moisture, evapotranspiration, and climatic water deficit were developed to (1) illustrate changes between recent, drought, and future climate conditions, (2) illustrate the effects of reducing or eliminating fog drip for recent, drought, and future climate conditions, and (3) highlight areas of increased potential risk for wildfire during drought and future climate conditions. The results of these analyses can be used by natural resource managers in Hawaiʻi.

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USGS2021

Mapping biological soil crusts in a Hawaiian dryland

Historical and ongoing land use patterns in the Hawaiian Islands have degraded the Islands’ drylands, causing erosion and detrimentally affecting adjacent coastal marine ecosystems. Biological soil crust (biocrust) communities have been shown to increase soil stability in drylands worldwide, but their efficacy in mitigating soil erosion in Hawaiian drylands is largely unknown. Using a combination of field data and imagery collected by small unmanned aerial systems (sUAS), we mapped biocrusts and examined their influence on soil stability in the Kawaihae watershed, an erosion-prone dryland on leeward Hawai`i Island. We created classified maps of biocrust cover from imagery collected at three spatial resolutions (1.2, 2.1 and 2.8 cm/pixel) using the pixel-based Support Vector Machine (SVM) classifier and investigated the impacts of spatial resolution and biocrust level of development on classification accuracy. Our medium (2.1 cm) resolution image produced the highest overall classification accuracy when biocrust was treated as a single class (82.1%). We explored the spatial impacts of biocrusts on soil loss via sUAS-derived measurements of elevation change over a four-year time span. We found differences in soil loss among land cover types, but robustly quantifying these was a challenge, as much of the change fell below statistically significant limits of detection. We investigated the relationship between biocrust development and soil stability by conducting soil aggregate stability testing at the three biocrust levels of development (LODs) present at the study site. We found a significant increase in soil stability from soils without surface biocrusts (LOD score of 0) to those with biocrusts at any development level (LOD 1–3). Our research adds to the body of biocrust knowledge by presenting new information about biocrust distribution and soil stabilization capabilities in Hawaiian drylands. We also provide insights into the trade-offs between spatial resolution and classification accuracy for biocrust classification and land cover analysis.

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USGS2021

Crater growth and lava-lake dynamics revealed through multitemporal terrestrial lidar scanning at Kīlauea Volcano, Hawaiʻi

Lava lake surfaces display the tops of active magma columns and respond to eruption variables such as magmatic pressure, convection, degassing, and cooling, as well as interactions with the craters that contain them. However, they are challenging to study owing to the numerous hazards that accompany these eruptions, and they are typically difficult to observe because the emitted gas plumes obscure the lava lake surfaces. The 2008–2018 Overlook crater and lava lake at Kīlauea Volcano, Hawaiʻi, provided a remarkable opportunity to study several high-resolution data streams of eruption variables that impacted the lava lake. To investigate how the crater and associated lava lake responded to changes in these eruption variables, we acquired terrestrial light detection and ranging (lidar) surveys of the Overlook crater and lava lake surface from February 2012 through December 2013, supplemented with several earlier terrestrial and airborne lidar datasets, to quantitatively track changes in the shape of the lava lake surface and the crater walls. Lidar captures high-resolution data even when the lake is completely obscured by thick gas plumes. We used a novel “unrolling technique” to map volumetric changes in crater shape, because standard elevation differencing fails to capture all topographic changes on the nearly vertical, and sometimes overhanging, crater walls. We measured crater perimeter growth rates of approximately 52 meters per year from 2009 to 2013, with the greatest growth occurring along a line linking areas of persistent upwelling and downwelling. We suggest that the development of an oblong crater with a perimeter that grows linearly is best explained by a model where degradation is favored at the sites of persistent upwelling and downwelling and where growth is controlled by a lithology that varies little with respect to rock strength. We also found that most of the Overlook crater growth occurred during a relatively small number of significant rockfall events (~16) over this period. Additional lidar datasets revealed that the lava lake surface has a measurable slope from the areas of persistent upwelling to downwelling, although rockfalls from the crater walls temporarily changed the direction of crustal plate movement along with the magnitude and direction of the lava lake surface slope. Our study demonstrates that lidar is an effective tool for tracking the topography of an active volcanic crater when heavy outgassing renders other tools, such as structure from motion, ineffective.

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USGS2021

New insights on faulting and intrusion processes during the June 2007, East Rift Zone eruption of Kilauea volcano, Hawai'i

The East Rift Zone (ERZ) of Kīlauea Volcano, Hawai'i, represents one of the most volcanically active regions in the world. The 2007 Father's Day (FD) dike intrusion, eruption, and accompanying slow-slip event (SSE) has been previously modeled using geodetic data to constrain the geometry of the intrusion and the timing and magnitude of the SSE. Here, we perform inversions of three interferometric synthetic aperture radar (InSAR) datasets and a new intensity offset tracking dataset to assess the effect of integrating intensity cross-correlation offsets into inversion problems and explore additional potential models for the intrusion geometry of the FD event based on this additional data. The overall lowest misfit single Okada model for all datasets opens 2.3 m, strikes 73 degrees while dipping sub-vertically at 83 degrees, and extends approximately 2.9 km to the ENE and 2.4 km downdip. The differences are minor between complex en-echelon distributed Okada and decollement model of (Montgomery-Brown et al., 2010) or 3D-MBEM breaching models including multiple surface breaches and free-slipping decollement movement. Finally, we examine the static Coulomb stress changes for the proposed decollement fault created by our preferred model and a representative model of deep rift opening and find that deep rift zones dilation, not shallow ERZ intrusions, are likely modulating slip on the decollement.

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USGS2021

Proportions, timing, and re-equilibration progress during the 1959 Summit Eruption of Kīlauea: An example of magma mixing processes operating during OIB petrogenesis

Petrographic and chemical analysis of scoria samples collected during the 1959 Kīlauea summit eruption illustrates the progress of thermal and chemical homogenization of the melts, and the gradual growth and/or re-equilibration of olivine phenocrysts, over the course of the eruption. Glass compositions show that thermal equilibration was largely complete within the span of the eruption, whereas chemical homogenization was a work in progress. The olivine phenocryst population, known to contain conspicuous antecrystic components, is also hybrid within the euhedral population. The bulk of the olivine reached the level of the erupting magma on November 18–19, 1959. Zoning patterns in olivine phenocrysts show that initially unzoned grains developed normal zoning by the end of the eruption. Reverse zoning in relatively Fe-rich olivine phenocrysts (interpreted as cognate to the stored magma) was progressively eliminated from November 21 to December 19, 1959, by diffusive re-equilibration between crystals and melt. Toward the end of the eruption, the only olivine composition in direct contact with the melt was Fo 84–86 , with the original rim compositional heterogeneity gone in 4–5 weeks’ time. Activity in December 1959 differed from that in November, as high fountaining events were more closely spaced and almost all samples were picritic, with bulk MgO ≥16·5 wt%. Three different levels were in play during the 1959 eruption: a deep source for high-MgO melts and forsteritic (Fo 87–89 ) olivines, an intermediate source for the bulk of the stored magma, and a shallower source for the most differentiated magma. This model is consistent with geophysical, petrological and chemical observations. Comparison of the 1959 eruption with results from older explosive deposits suggests that stored and recharge melts and olivine from the deeper parts of Kīlauea’s plumbing are similar in composition to those observed or inferred in the 1959 eruption, so they behave similarly during extrusive and explosive periods alike.

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USGS2021

Geologic map of the State of Hawaii

This geologic map and its digital databases present the geology of the eight major islands of the State of Hawaiʻi. The map should serve as a useful guide to anyone studying the geologic setting and history of Hawai‘i, including ground- and surface-water resources, economic deposits, and landslide or volcanic hazards. Its presentation in digital format allows the rapid application of geologic knowledge when conducting field work; analyzing land-use or engineering problems; studying onshore or nearshore biologic communities; or simply understanding the relation between the geology, scenery, and cultural history of the Hawaiian paradise. The map includes a Description of Map Units, which describes the lithologic characteristics and distribution of the geologic deposits. A Correlation of Map Units shows how the different geologic formations are related to each other stratigraphically. A fairly complete geospatial database of the radiometric ages and geochemical analyses has been compiled from findings published over the past 100 years by numerous Earth scientists working across the island chain.

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USGS2021

A decade of geodetic change at Kīlauea’s summit—Observations, interpretations, and unanswered questions from studies of the 2008–2018 Halemaʻumaʻu eruption

On March 19, 2008, a small explosion heralded the onset of an extraordinary eruption at the summit of Kīlauea Volcano. The following 10 years provided unprecedented access to an actively circulating lava lake located within a region monitored by numerous geodetic tools, including Global Navigation Satellite System (GNSS), interferometric synthetic aperture radar (InSAR), tilt, and gravity. These datasets revealed a range of processes occurring on widely different timescales. Over years, pressure change within the summit magmatic system, determined from ground deformation and lava-lake surface height, seems to have been governed by broad variations in the rate of magma supply from the mantle to the volcano’s shallow magmatic system, as well as changes in the efficiency of East Rift Zone (ERZ) magma transport and eruption. Over weeks to months, intrusions at the summit and along the ERZ, where new eruptive vents commonly formed and intrusions were primed by extension from south-flank motion, were a result of short-term increases in magma supply or waning lava effusion from the ERZ. Waning lava effusion caused magma to back up behind the ERZ eruptive vent all the way to the summit. ERZ intrusions and eruptions caused rapid depressurization of the summit magmatic system, whereas summit intrusions resulted in complex deformation patterns as magma moved to and from two main sub-caldera storage areas. Over hours to days, pressure changes were caused by episodic deflation-inflation (DI) events and possibly small summit intrusions, and deformation of the rim of the summit eruptive vent revealed instabilities that indicated an increased potential for collapse and minor explosive activity. Finally, over timescales of minutes to hours, gas pistoning, summit explosions, very-long-period seismic events, and even the airborne eruptive plume had clear manifestations in geodetic datasets, providing insights into the causes and consequences of those processes. The diversity and quantity of geodetic observations shed important light on this exceptional and well-documented decade-long summit eruption and its accompanying phenomena, yet numerous questions remain about the causal mechanisms, physical processes, and magmatic conditions associated with eruptive and intrusive activity.

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USGS2021

High-speed lava flow infrasound from Kīlauea’s fissure 8 and its utility in monitoring effusion rate

The 2018 eruption of Kīlauea Volcano produced large and destructive lava flows from the fissure 8 (Ahu ‘aila ‘au) vent with flow velocities up to 17 m s −1 , highly variable effusion rates over both short (minutes) and long (hours) time scales, and a proximal channel or spillway that displayed flow features similar to open channel flow in river systems. Monitoring such dynamic vent and lava flow systems is a challenge. Our results demonstrate that infrasound, combined with ground-based observations and imagery from unoccupied aircraft systems (UAS), can be used to distinguish vent degassing activity from high-speed lava flow activity. We use spectral characteristics and the infrasound frequency index (FI) to distinguish spillway infrasound from vent infrasound. Comparing FI with flow speeds derived from UAS videos reveals that spillway infrasound only occurs when flow speeds were sufficiently high to cause a supercritical flow state and breaking waves (Froude values > 1.7), and we propose that the spillway signals are produced primarily through the interaction of the turbulent lava-free surface with the atmosphere. We show that FI can also provide a means to track bulk effusion rate. Our results indicate that infrasound offers a new way to characterize lava flow channel hydraulics and is a powerful tool for monitoring effusive eruptions when high-speed flows are possible.

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USGS2021

Evaluating lava flow propagation models with a case study from the 2018 eruption of Kīlauea Volcano, Hawai'i

The 2018 lower East Rift Zone (LERZ) eruption of Kīlauea, Hawai’i, provides an excellent natural laboratory with which to test models of lava flow propagation. During early stages of eruption crises, the most useful lava flow propagation equations utilize readily determined parameters and require fewer a priori assumptions about future behavior of the flow. Here, we leverage the numerous observations of lava flows collected over the duration of the eruption crisis at Kīlauea in 2018 to test simple lava flow propagation models. These models track the one-dimensional propagation of the flows according to three main rheological restraining forces: bulk viscosity, yield strength, and growth of a surface crust. We calculate the predicted changes in length through time of three flows that vary in bulk composition, crystal content, and total flow length. Cooler flows that are more crystal-rich tend to be more dominated by crust growth, though early stages of propagation can be controlled by bulk viscosity. We find that variations in effusion rate significantly impact flows that are short-lived; flows that are produced during steady-state effusion are readily approximated by average values for the entire flow. Thus, accurate knowledge of variations in effusion rate are critical to accurate lava flow propagation forecasting.

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USGS2021

Density structure of the island of Hawai’i and the implications for gravity-driven motion of the south flank of Kilauea volcano

The discovery that large landslides dissected the Hawaiian islands, scattering debris over thousands of square kilometers of seafloor, changed our ideas of island growth and evolution. The evidence is consistent with catastrophic flank collapse during volcano growth, and draws our focus to the currently active island of Hawai’i, the volcanoes Mauna Loa and Kīlauea, and particularly to the actively-mobile south flank of Kīlauea volcano. Both the weight distribution and pressure within an extensive magma system are perceived to affect stability, but the role of gravitational body forces and island density distribution has not been quantitatively assessed. We use seismic velocities derived from tomography to model the density distribution of the island of Hawai’i and find that olivine-rich melts and rocks in Hawaiian volcanoes result in a close association of seismic velocity and density. The resultant density model reproduces more than 95% of the observed gravity disturbance signal wherever tomographic control exists and provides a basis for evaluating the body forces from gravity. We also find that if the decollement is weak, then gravitational body forces can produce slip that explains most seismo-tectonic and volcano-tectonic structural features of Kīlauea volcano. Where the decollement is in a state of incipient slip from this weight distribution, fluctuations in magma pressure can trigger accelerated slip on the decollement. Yet this is only true of the south flank of Kīlauea volcano. Though weight and magma distributions produce significant forces driving the west flank of Mauna Loa seaward, this flank is stable. Stability over the last decade indicates a strong foundation beneath the west flank of Mauna Loa, perhaps as a result of large debris avalanches that occurred there that scraped clay-rich sediments off of the decollement.

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USGS2021

Ecosystem carbon balance in the Hawaiian Islands under different scenarios of future climate and land use change

The State of Hawai'i passed legislation to be carbon neutral by 2045, a goal that will partly depend on carbon sequestration by terrestrial ecosystems. However, there is considerable uncertainty surrounding the future direction and magnitude of the land carbon sink in the Hawaiian Islands. We used the Land Use and Carbon Scenario Simulator (LUCAS), a spatially explicit stochastic simulation model that integrates landscape change and carbon gain-loss, to assess how projected future changes in climate and land use will influence ecosystem carbon balance in the Hawaiian Islands under all combinations of two radiative forcing scenarios (RCPs 4.5 and 8.5) and two land use scenarios (low and high) over a 90 year timespan from 2010 to 2100. Collectively, terrestrial ecosystems of the Hawaiian Islands acted as a net carbon sink under low radiative forcing (RCP 4.5) for the entire 90 year simulation period, with low land use change further enhancing carbon sink strength. In contrast, Hawaiian terrestrial ecosystems transitioned from a net sink to a net source of CO 2 to the atmosphere under high radiative forcing (RCP 8.5), with high land use accelerating this transition and exacerbating net carbon loss. A sensitivity test of the CO 2 fertilization effect on plant productivity revealed it to be a major source of uncertainty in projections of ecosystem carbon balance, highlighting the need for greater mechanistic understanding of plant productivity responses to rising atmospheric CO 2 . Long-term model projections such as ours that incorporate the interactive effects of land use and climate change on regional ecosystem carbon balance will be critical to evaluating the potential of ecosystem-based climate mitigation strategies.

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USGS2021

Post audit of simulated groundwater flow to a short-lived (2019-2020) crater lake at Kīlauea Volcano

About 14.5 months after the 2018 eruption and summit collapse of Kīlauea Volcano, Hawaiʻi, liquid water started accumulating in the deepened summit crater, forming a lake that attained 51 m depth before rapidly boiling off on December 20, 2020, when an eruption from the crater wall poured lava into the lake. Modeling the growth of the crater lake at Kīlauea summit is important for assessing the potential for explosive volcanism. Our current understanding of the past 2500 years of eruptive activity at Kīlauea suggests a slight dominance of explosive behavior over effusive. The deepened summit crater and presence of the crater lake in 2019 raised renewed concerns about explosive activity. Groundwater models using hydraulic-property data from a nearby drillhole successfully forecast the timing and rate of lake filling. Here we compare the groundwater-model predictions with observational data through the demise of the crater lake, examine the implications for local water-table configuration, consider the potential role of evaporation and recharge (neglected in previous models), and briefly discuss the energetics of the rapid boil-off. This post audit of groundwater-flow models of Kīlauea summit shows that simple models can sometimes be used effectively to simulate complex settings such as volcanoes.

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USGS2021

Understanding grass invasion, fire severity, and Acacia koa regeneration for forest restoration in Hawaiʻi Volcanoes National Park

With invasive grasses increasing wildfire occurrence worldwide, a better understanding of the relationships between native plants, fire, and invasive grass is needed to help restoration plans facilitate ecosystem resilience. Invasive grasses are particularly problematic for altering fire regimes in the tropics, yet in Hawaiʻi, restoration sites are often planted with monocultures of the native tree Acacia koa, which can promote grass growth via nitrogen fixation. This, combined with the difficulty of estimating pre-fire grass cover under thick canopies, complicates attempts to restore Hawaiian ecosystems. We studied the 2018 Keauhou Ranch Fire in Hawaiʻi to investigate three questions: (1) at what level of precision can pre-fire grass cover be accurately estimated from oblique aerial photos? (2) how are post-fire A. koa regeneration densities affected by fire severity? and (3) how are post-fire A. koa regeneration densities affected by pre-fire grass cover and its interaction with fire severity? We collected burn severity and post-fire regeneration data from 30 transects stratified across mid-elevation woodland, montane woodland, and montane shrubland communities. We evaluated visual estimates of pre-fire grass cover from oblique aerial imagery with quantitative in situ data from 60 unburned transects of the same cover types. Pre-fire estimates of grass cover categories were 67% accurate in montane woodland ( n = 9) and 100% accurate in montane shrubland ( n = 11), but only 20% accurate in mid-elevation woodland ( n = 10). In montane woodlands with low pre-fire tree densities, A. koa regeneration densities were higher with increased fire severity, but this trend reversed when pre-fire tree densities were high. We detected no effect of pre-fire grass cover, nor its interaction with fire severity, on A. koa regeneration density. This indicates that restoration through the planting of A. koa may be successful in promoting fire-resilient A. koa forest, although there are potential issues to consider regarding the effects that A. koa ’s grass promotion may have on other species within the ecosystem.

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USGS2021

Repeating caldera collapse events constrain fault friction at the kilometer scale

Fault friction is central to understanding earthquakes, yet laboratory rock mechanics experiments are restricted to, at most, meter scale. Questions thus remain as to the applicability of measured frictional properties to faulting in situ. In particular, the slip-weakening distance d c "> d c dc strongly influences precursory slip during earthquake nucleation, but scales with fault roughness and is challenging to extrapolate to nature. The 2018 eruption of K̄ılauea volcano, Hawaii, caused 62 repeatable collapse events in which the summit caldera dropped several meters, accompanied by M W "> M W MW 4.7 to 5.4 very long period (VLP) earthquakes. Collapses were exceptionally well recorded by global positioning system (GPS) and tilt instruments and represent unique natural kilometer-scale friction experiments. We model a piston collapsing into a magma reservoir. Pressure at the piston base and shear stress on its margin, governed by rate and state friction, balance its weight. Downward motion of the piston compresses the underlying magma, driving flow to the eruption. Monte Carlo estimation of unknowns validates laboratory friction parameters at the kilometer scale, including the magnitude of steady-state velocity weakening. The absence of accelerating precollapse deformation constrains d c "> d c dc to be ≤ 10 "> ≤ 10 ≤10 mm, potentially much less. These results support the use of laboratory friction laws and parameters for modeling earthquakes. We identify initial conditions and material and magma-system parameters that lead to episodic caldera collapse, revealing that small differences in eruptive vent elevation can lead to major differences in eruption volume and duration. Most historical basaltic caldera collapses were, at least partly, episodic, implying that the conditions for stick–slip derived here are commonly met in nature.

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USGS2021

Individual and seasonal variation in the movement behavior of two tropical nectarivorous birds

Background Movement of animals directly affects individual fitness, yet fine spatial and temporal resolution movement behavior has been studied in relatively few small species, particularly in the tropics. Nectarivorous Hawaiian honeycreepers are believed to be highly mobile throughout the year, but their fine-scale movement patterns remain unknown. The movement behavior of these crucial pollinators has important implications for forest ecology, and for mortality from avian malaria ( Plasmodium relictum ), an introduced disease that does not occur in high-elevation forests where Hawaiian honeycreepers primarily breed. Methods We used an automated radio telemetry network to track the movement of two Hawaiian honeycreeper species, the ʻapapane ( Himatione sanguinea ) and ʻiʻiwi ( Drepanis coccinea ). We collected high temporal and spatial resolution data across the annual cycle. We identified movement strategies using a multivariate analysis of movement metrics and assessed seasonal changes in movement behavior. Results Both species exhibited multiple movement strategies including sedentary, central place foraging, commuting, and nomadism , and these movement strategies occurred simultaneously across the population. We observed a high degree of intraspecific variability at the individual and population level. The timing of the movement strategies corresponded well with regional bloom patterns of ‘ōhi‘a ( Metrosideros polymorpha ) the primary nectar source for the focal species. Birds made long-distance flights, including multi-day forays outside the tracking array, but exhibited a high degree of fidelity to a core use area, even in the non-breeding period. Both species visited elevations where avian malaria can occur but exhibited little seasonal change in elevation (< 150 m) and regularly returned to high-elevation roosts at night. Conclusions This study demonstrates the power of automated telemetry to study complex and fine-scale movement behaviors in rugged tropical environments. Our work reveals a system in which birds can track shifting resources using a diverse set of movement behaviors and can facultatively respond to environmental change. Importantly, fidelity to high-elevation roosting sites minimizes nocturnal exposure to avian malaria for far-ranging individuals and is thus a beneficial behavior that may be under high selection pressure.

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