Solid Earth Research Articles

Spatial variability of marine-terminating ice sheet retreat in the Puget Lowland

Abstract. Understanding drivers of marine-terminating ice sheet behavior is important for constraining ice contributions to global sea level rise. In part, the stability of marine-terminating ice is influenced by solid Earth conditions at the grounded-ice margin. While the Cordilleran Ice Sheet (CIS) contributed significantly to global mean sea level during its final post-Last-Glacial-Maximum (LGM) collapse, the drivers and patterns of retreat are not well constrained. Coastal outcrops in the deglaciated Puget Lowland of Washington State – largely below sea level during glacial maxima, then uplifted above sea level via glacial isostatic adjustment (GIA) – record the late Pleistocene history of the CIS. The preservation of LGM glacial and post-LGM deglacial sediments provides a unique opportunity to assess the variability in marine ice sheet behavior of the southernmost CIS. Based on paired stratigraphic and geochronological work, with a newly developed marine reservoir correction for this region, we identify that the late-stage CIS experienced stepwise retreat into a marine environment between 15 000 and 14 000 years before present, consistent with timing of marine incursion into the region reported in earlier works. Standstill of marine-terminating ice for at least 500 years, paired with rapid vertical landscape evolution, was followed by continued retreat of ice in a subaerial environment. These results suggest rapid rates of solid Earth uplift and topographic support (e.g., grounding zone wedges) stabilized the ice margin, supporting final subaerial ice retreat. This work leads to a better understanding of shallow-marine and coastal-ice-sheet retreat and is relevant to sectors of the contemporary Antarctic and Greenland ice sheets and marine-terminating outlet glaciers.

2D FDM Simulation of Seismic Waves and Tsunamis Based on Improved Coupling Equations Under Gravity

AbstractTo understand the characteristics of seismic waves and tsunamis recorded simultaneously by the ocean-bottom observation networks, the coupling between the solid Earth and the ocean has to be modeled in the presence of gravity. However, previous coupled simulations adopted approximate equations that did not fully incorporate the effects of gravity. In this study, we derived correctly linearized governing equations under gravity and compared them with those of previous studies. Numerical experiments were performed for a two-dimensional P-SV wavefield, using the finite difference method (FDM). To validate the accuracy of the calculated tsunamis, we computed the theoretical tsunami dispersion relation using a propagator matrix and compared it with our results and those of previous studies. We found that our proposed method provided more accurate results than those of previous studies, particularly in the short-period band. We also investigated the applicability of the proposed method to distant tsunamis by examining the difference between calculated and theoretical tsunami phase velocities in the long-period band. The proposed formulation provides accurate results that properly incorporate gravity into the simultaneous simulation of seismic waves and tsunamis.

Statistical appraisal of geothermal heat flow observations in the Arctic

Abstract. Geothermal heat flow is an important boundary condition for ice sheets, affecting, for example, basal melt rates, but for ice-covered regions, we only have sparse heat flow observations with partly high uncertainty of up to 30 m W m−2. In this study, we first investigate the agreement between such pointwise heat flow observations and solid Earth models, applying a 1D steady-state approach to perform a statistical analysis for the entire Arctic region. We find that most of the continental heat flow observations have a high reliability and agreement to solid Earth models, except a few data points, such as, for example, the NGRIP (North Greenland Ice Core Project) point in central Greenland. For further testing, we perform a conditional simulation with focus on Greenland in which the local characteristics of heat flow structures can be considered. Simple kriging shows that including or excluding the less reliable NGRIP point has a large influence on the surrounding heat flow. The geostatistical analysis with the conditional simulation supports the assumption that NGRIP might not only be problematic for representing a regional feature but likely is an outlier. Basal melt estimates show that such a local spot of high heat flow results in local high basal melt rates but leads to less variation than existing geophysical models.

Glacial inception through rapid ice area increase driven by albedo and vegetation feedbacks

Abstract. We present transient simulations of the last glacial inception using the Earth system model CLIMBER-X with dynamic vegetation, interactive ice sheets, and visco-elastic solid Earth responses. The simulations are initialized at the middle of the Eemian interglacial (125 kiloyears before present, ka) and run until 100 ka, driven by prescribed changes in Earth's orbital parameters and greenhouse gas concentrations from ice core data. CLIMBER-X simulates a rapid increase in Northern Hemisphere ice sheet area through MIS5d, with ice sheets expanding over northern North America and Scandinavia, in broad agreement with proxy reconstructions. While most of the increase in ice sheet area occurs over a relatively short period between 119 and 117 ka, the larger part of the increase in ice volume occurs afterwards with an almost constant ice sheet extent. We show that the vegetation feedback plays a fundamental role in controlling the ice sheet expansion during the last glacial inception. In particular, with prescribed present-day vegetation the model simulates a global sea level drop of only ∼ 20 m, compared with the ∼ 35 m decrease in sea level with dynamic vegetation response. The ice sheet and carbon cycle feedbacks play only a minor role during the ice sheet expansion phase prior to ∼ 115 ka but are important in limiting the deglaciation during the following phase characterized by increasing summer insolation. The model results are sensitive to climate model biases and to the parameterization of snow albedo, while they show only a weak dependence on changes in the ice sheet model resolution and the acceleration factor used to speed up the climate component. Overall, our simulations confirm and refine previous results showing that climate–vegetation–cryosphere feedbacks play a fundamental role in the transition from interglacial to glacial states characterizing Quaternary glacial cycles.

National-scale Geochemical Survey: Distribution of chemical elements in stream sediment of South and Central Asia

This work was carried out as the Pakistani, Uzbekistani, Tajikistani, and Kyrgyzstani contribution to the National-scale Geochemical Survey of South and Central Asia (NGSSCA) project, the objective of which was to document and study the amounts and distribution of chemical elements in stream sediment of South and Central Asia where such national-scale geochemical mapping is launched for the first time. In the framework of the NGSSCA project deployed in Pakistan, Uzbekistan, Tajikistan, and Kyrgyzstan, 9237 stream sediment samples (<2 mm grain-size fraction in alpine desert and mountainous area) were collected at an average density of 1 sample site/100 km2, on the basis of a common stream sediment sampling protocol. The resultant compositional data sets and cartographic products will vastly benefit future mineral exploration activity, surficial (and even solid Earth) geochemical processes studies (e.g., chemical weathering), and environmental evaluation. Eight elements of economic interests (e.g., Ag, Sb, W, Mo, Li, Be, Cu, and Co) are selected to demonstrate their distribution pattern in stream sediment and the main controlling factors. It's concluded that the anomalies for the selected elements in the NGSSCA project can thus be directly linked to different geogenic sources, e.g., underlying bedrock, soil type, mineralization or ore deposits, and large-scale fault systems. Based on the results and the integrated anomaly maps, some new target areas for the corresponding metallic mineralization are predicted, which will provide a basis for further mineral exploration.

Long‐ and Short‐Term Effects of Seismic Waves and Coseismic Pressure Changes on Fractured Aquifers

AbstractTwo adjacent groundwater wells on the North China Platform are used to study how earthquakes impacted aquifers. We use the response of water level to solid Earth tides to document changes after earthquakes and how aquifer and fracture properties recovered to pre‐earthquake properties. We consider two models for the phase and amplitude of water level response to the lunar diurnal (O1) and semidiurnal (M2) tides: a leaky aquifer model, and a model in which fracture orientation determines the response. In the leaky aquifer model, changes arise from changes in permeability and storage; in the fracture model, changes are due to changes in apparent orientation of transmissive fractures. Responses in one well are best explained by the leaky aquifer model, and can explain the large amplitude coseismic water level and permeability changes and the non‐recoverable changes after the largest earthquake. Responses in the other well are consistent with the fracture model and show little coseismic change in water level but changes in apparent fracture orientation. Larger ground motions lead to larger coseismic water level changes and longer recovery times. We propose that the well in the more permeable and shallow aquifer has less variable pore‐pressures around the well. Larger coseismic strains from water level changes may enable longer‐lasting changes in aquifer properties. We conclude that relatively high permeability aquifers are less susceptible to impacts from seismic waves, and thus have small changes in water levels and hydrogeological properties.

Introducing the new Editor-in-Chief of &lt;em&gt;JGR: Solid Earth&lt;/em&gt;

Learn about the person taking the helm of JGR: Solid Earth and his vision for the coming years.

Reflecting on 4 Years at the helm of &lt;em&gt;JGR: Solid Earth&lt;/em&gt;

The outgoing Editor-in-Chief of JGR: Solid Earth reflects on their tenure and expresses appreciation to all those who contributed to the success of the journal over recent years.

Rock-mass heterogeneous rheological properties caused the formation of deep tension fractures

Tension failure is a unique phenomenon in solid Earth that occurs on scales ranging from large plate rift valleys to small laboratory rocks. On a slope scale, deep unloading tension fractures are distinct from conventional unloading fractures and are a unique geological phenomenon in valleys with high in-situ stress. To accurately reproduce the development and evolution of deep unloading tension fractures and to support major excavation projects, a series of works including geological investigation, laboratory tests, intrinsic model establishment, and numerical simulation were carried out in this study. The unloading rheological tests, accounting for time-dependent effects, uncover the heterogeneity in the rheological attributes of rock-mass strength parameters during valley downcutting. This heterogeneity manifests as a transition in rock-mass strength parameters that cohesion weakening-friction strengthening (CWFS). Drawing on the results of laboratory tests, a novel viscoelastic-plastic model, termed the WSR model, was proposed. This model takes into account both CWFS and rheological considerations. It has been applied to simulate deep unloading tension fractures in the Jinping I hydropower station (JP-I) and compared with conventional models. The results show that WSR model accurately reproduced the development and evolution of deep unloading tension fractures and the heterogeneity of rock-mass deformation during age evolution leads to the formation of deep unloading tension fractures. In this study, the rock-mass heterogeneous rheological properties were summarized as the heterogeneity of the rock-mass strength parameters during age deterioration and the heterogeneity of rock-mass deformation during age evolution; the WSR model was proposed to characterize the heterogeneous rheological property of rock-mass strength parameters and to reproduce the development and evolution of deep unloading tension fractures in the JP-I. This novel contribution to deep unloading tension fractures emphasizes that the rock-mass heterogeneous rheological properties lead to the formation of deep unloading tension fractures.

Holocene southwest Greenland ice sheet behavior constrained by sea-level modeling

The melting of the Greenland ice sheet (GrIS) is a major contributor to past and future global sea-level rise. Understanding the response of the GrIS to times in the past when temperatures were as warm or warmer than today offers insights into its current and future response to climate change. In the southwest sector, the GrIS retreated inland beyond its current margin during the (at least regionally) warmer-than-present mid-Holocene, before it readvanced to the historical maximum position during the Little Ice Age. This was then followed by a slight retreat to its current position. To investigate the timing and magnitude of southwest GrIS retreat and readvance in response to Holocene warmth, we model the response of the solid Earth and local relative sea level (RSL) to past ice sheet change. We test a suite of eleven ice sheet scenarios that are based on ICE-6G_C but are modified in the timing and magnitude of ice retreat and readvance and pair them with four different viscoelastic Earth structures. We compare model predictions to observations of paleo sea level, present-day sea-level change, and present-day vertical land motion (VLM) around Nuuk, Greenland. We find that the modeled timing and magnitude of the Holocene retreat and readvance have a significant impact on modern sea-level change and VLM in Nuuk. Models that assume a readvance approaching the southwest GrIS’ historical maximum between 2 and 1 ka are most consistent with observations. The RSL response, however, is less sensitive to the timing of the minimum GrIS extent. Nonetheless, better data-model fits are generally obtained when the minimum ice sheet extent is reached between 5 and 3 ka, within the tested range of 6-3 ka. Comparing this timing to local and regional records of temperature and ice-sheet change suggest that the evolution of the southwestern GrIS presented here was in-phase with the likely evolution of southwestern GrIS mass balance through the Holocene. Our results have implications for future ice sheet modeling studies targeting southwestern Greenland by providing additional constraints and strengthening existing ones. Moreover, this work provides a deeper understanding of the interactions between the climate and the cryosphere and thus of future ice sheet change.

How to build a habitable planet: an interview with Charles H. Langmuir

Abstract Earth is the only known habitable planet in the solar system. Understanding how Earth developed its unique habitability has been the frontier of Earth sciences and has become one of the main themes of current deep-space explorations. What are the decisive factors that led to a habitable planet? What is the role of solid Earth processes in the origin of life and in modulating the surface environment? Are Earth's habitability studies relevant to current challenges that human beings face? These questions have attracted the interest of both scientists and the public alike. NSR spoke to Prof. Charles H. Langmuir from Harvard University in the USA, who is a solid Earth geochemist who carries out research on diverse aspects of the plate tectonic geochemical cycle, including ocean ridges, convergent margins and intraplate volcanism. Prof. Langmuir is the author of the book How to Build a Habitable Planet (www.habitableplanet.org), one of the best Earth science books published in 2012.

Methane genesis within olivine-hosted fluid inclusions in dolomitic marble of the Hida Belt, Japan

Abiotic synthesis of hydrocarbon-bearing fluids during geological processes has a significant impact on the evolution of both the Earth's biosphere and the solid Earth. Aqueous alteration of ultramafic rocks, i.e., serpentinization, which forms serpentinite, is one of the geological processes generating abiotic methane (CH4). However, abiotic CH4 generation is not limited to the serpentinization of mafic and ultramafic lithologies. Metasedimentary dolomitic marble from the Hida Belt, Japan, is characterized by the presence of forsterite-rich olivine (Fo~89–93), and olivine crystals contain abundant fluid inclusions (<1 to 10 μm in size). Raman spectroscopic analyses of olivine-hosted fluid inclusions found that both primary and secondary fluid inclusions contain CH4, lizardite/chrysotile, and brucite. This indicates that micro-scale interactions between COH fluid and host olivine produced CH4 through the reduction of CO2 by H2 released during local serpentinization within inclusions. Our observation implies that the dolomitic marble has the potential to be a key lithology for the synthesis and storage of abiotic CH4 in a shallower crustal portion of orogenic belts.

Characterization and spatiotemporal variations of ambient seismic noise in eastern Bangladesh

This study analyses the ambient noise field recorded by the seismic network, TREMBLE, in Bangladesh, operational since late 2016. Horizontal-vertical spectral ratios confirm the placement of stations on sediment, many situated on thick sedimentary columns, consistent with local geology. Noise across the broadband spectrum is systematically examined. A high amplitude local microseism (0.4–0.8 Hz) is recorded, originating near the coast and modulated by local tides. The secondary microseism (0.15–0.35 Hz) correlates strongly with wave height in the Bay of Bengal and varies with seasons, with greater power and higher horizontal amplitude in the monsoon season when the wave height is highest. The microseism increases in amplitude and decreases in frequency as a tropical depression moves inland. The primary microseism (∼0.07–0.08 Hz) exhibits no seasonal changes in power but display strong horizontal energy which changes with seasons. Low frequency (0.02–0.04 Hz) noise on the horizontal components has a 24-h periodicity, due to instrument tilt caused by atmospheric pressure changes. A station located next to the major Karnaphuli River shows elevated energy at ∼5 Hz correlated to periods of high rainfall. Anthropogenic noise (∼4–14 Hz) is station-dependent, demonstrating changing patterns in human activity, such as during Ramadan, national holidays and the COVID pandemic. Our work holds implications for seismic deployments, earthquake, and imaging studies, while providing insights into the interaction between the atmosphere, ocean, and solid Earth.

GRACE and GRACE Follow‐On Gravity Observations of Intermediate‐Depth Earthquakes Contrasted With Those of Shallow Events

AbstractEarthquakes involve mass redistribution within the solid Earth and the ocean, and as a result, perturb the Earth's gravitational field. For most of the shallow (&lt;60 km) earthquakes with Mw &gt; 8.0, the GRACE satellite gravity measurements suggest considerable volumetric disturbance of rocks. At a spatial scale of hundreds of km, the effect of volumetric change exceeds gravity change by vertical deformation; for example, negative gravity anomalies associated with volumetric expansion are characteristic patterns after shallow thrust events. In this study, however, we report contrasting observations of gravity change from two intermediate‐depth (100–150 km) earthquakes of 2016 &amp; 2017 Mw 8.0 (two combined) Papua New Guinea thrust faulting events and 2019 Mw 8.0 Peru normal faulting and highlight the importance of compressibility in earthquake deformation. The combined 2016/17 thrust events resulted in a positive gravity anomaly of 5–6 microGal around the epicenter, while the 2019 normal faulting produced a negative gravity anomaly of 3–4 microGal. Our modeling found that these gravity changes are manifestation of vertical deformation with limited volumetric change, distinct from gravity changes after the shallow earthquakes. The stronger resistance of rocks to volume change at intermediate‐depth results in largely incompressible deformation and thus in a gravity change dominated by vertical deformation. In addition, malleable rocks under high pressure and temperature at depth facilitated substantial afterslip and/or fast viscoelastic relaxation causing additional vertical deformation and gravity change equivalent to the coseismic change. For the Papua New Guinea events, this means that postseismic relaxation enhanced coseismic uplift and relative sea level decrease.

On Dislocation Climb as an Important Deformation Mechanism for Planetary Interiors

▪ An understanding of the rheological behavior of the solid Earth is fundamental to provide a quantitative description of most geological and geophysical phenomena. The continuum mechanics approach to describing large-scale phenomena needs to be informed by a description of the mechanisms operating at the atomic scale. These involve crystal defects, mainly vacancies and dislocations. This often leads to a binary view of creep reduced to diffusion creep or dislocation creep. However, the interaction between these two types of defects leading to dislocation climb plays an important role, and may even be the main one, in the high-temperature, low strain rate creep mechanisms of interest to the Earth sciences. Here we review the fundamentals of dislocation climb, highlighting the specific problems of minerals. We discuss the importance of computer simulations, informed by experiments, for accurately modeling climb. We show how dislocation climb increasingly appears as a deformation mechanism in its own right. We review the contribution of this mechanism to mineral deformation, particularly in Earth's mantle. Finally, we discuss progress and challenges, and we outline future work directions. Dislocations can be sources or sinks of vacancies, resulting in a displacement out of the glide plane: climb. ▪ Dislocation climb can be a recovery mechanism during dislocation creep but also a strain-producing mechanism. ▪ The slow natural strain rates promote the contribution of climb, which is controlled by diffusion. ▪ In planetary interiors where dislocation glide can be inhibited by pressure, dislocation climb may be the only active mechanism. Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Halogen Cycling in the Solid Earth

Each of the halogens constrains a different aspect of volatile cycling in the solid Earth. F is moderately incompatible in the mantle and has a low mobility at Earth's surface, meaning that it is preferentially retained in the mantle and continental crust. In contrast, Cl, Br, and I are strongly incompatible and highly soluble. Chloride is the dominant anion in seawater and many geofluids and a major component of evaporite minerals. Br and I are essential for life and significantly incorporated into organic matter that accumulates in marine sediments. Surficial fluids circulated into continental and oceanic crust incorporate surface-derived halogens into alteration minerals. As a result, subducting slabs and arc lavas are weakly enriched in F and strongly enriched in Cl, Br, and I. Subduction has maintained mantle Cl and Br concentrations at relatively constant levels since Earth's early differentiation, but mantle I/Cl has decreased over time. ▪ Halogen abundances on the early Earth were affected by I partitioning into Earth's core and possible loss of hydrophilic Cl, Br, and I in an early formed ocean. ▪ Halogens are powerful tracers of subduction zone processes on the modern Earth, with Cl, Br, and I having a dominantly subducted origin in Earth's mantle. ▪ The deep subduction cycles of Cl, Br, and I are more similar to that of H2O than they are to F, but the geochemical cycle of each halogen differs in detail. ▪ Halogen abundance ratios and stable isotope ratios vary systematically in Earth's surface reservoirs, meaning that halogens are powerful tracers of geological fluids and melts. Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

On the role of volcanic plume heights in excitation of free oscillations of the solid Earth and atmosphere: Case study

Volcanic eruptions are potential sources for generating the Earth’s free oscillations at spheroidal modes of 0S29 and 0S37 through acoustic resonant coupling between the Earth and its atmosphere. Then, does every volcano produce Earth’s free oscillations? We answer this question by analyzing eight large volcanic eruption events, (i) 15 January 2022 Hunga Tonga-Hunga Ha apai (HTHH), (ii) 13–14 January 2022, HTHH, (iii) 13 August 2021 Fukutoku-Okanoba, (iv) 22 April 2015 Calbuco, (v) 13 February 2014 Kelud, (vi) 4 November 2010 Merapi, (vii) 15 June 1991 Mt Pinatubo, and (viii) 4 April 1982 El Chichon. Our analysis revealed that the 15 January HTHH, Mt. Pinatubo, and El Chichon eruptions excited the Earth’s free oscillations globally at spheroidal modes of 0S29 and/or 0S37 but no such modes were excited during other eruptions. However, harmonic oscillations in the ionosphere were seen during all recent eruption events. We demonstrate that stronger eruptions excite stronger atmospheric modes as the plume arrives at higher atmospheric heights which enable efficient ground-atmosphere acoustic resonant coupling for the excitation of spheroidal modes. Further, we hypothesize that relatively weaker eruptions/lower plume height perhaps caused weakly confined atmospheric modes thus failure of excitation of the spheroidal modes. A quantitative analysis of source efficiency versus source heights provides more insights into our hypothesis.

Atmospheric resonant oscillations by the 2022 January 15 eruption of the Hunga Tonga–Hunga Ha'apai volcano from GNSS-TEC observations

SUMMARY Continuous Plinian eruptions often excite atmospheric modes of ∼3.7 and ∼4.4 mHz, which are observed as harmonic oscillations of ionospheric total electron content (TEC) by global navigation satellite system (GNSS) receivers. Such TEC oscillations started shortly after the great eruption of the Hunga Tonga–Hunga Ha'apai (HTHH) submarine volcano at ∼4:14 UT, on 2022 January 15. Here I analyse GNSS data at stations within ∼4000 km from the volcano to study temporal and spatial distribution of such atmospheric modes. Strong ∼3.7 mHz TEC oscillations in near fields started shortly after the eruption onset and propagated outward with the sound speed from HTHH. Later such TEC oscillations became strong again with the amplitude peak at the distance ∼1400 km from HTHH. Such far field oscillations occurred also above New Zealand and the Solomon Islands, ∼3000 km from HTHH. Their amplitudes seem correlated with those of the 0S29 solid earth mode, suggesting that vertical surface vibrations underneath may play a role in maintaining the atmospheric mode. Onset of the far field TEC oscillations are synchronized with the local sunrise, possibly controlled by diurnal changes in the ionospheric electron density.

Centers for Innovation and Community Engagement in Solid Earth Geohazards (NSF)

Centers for Innovation and Community Engagement in Solid Earth Geohazards (NSF)

Sudden Commencements and Geomagnetically Induced Currents in New Zealand: Correlations and Dependance

AbstractChanges in the Earth's geomagnetic field induce geoelectric fields in the solid Earth. These electric fields drive Geomagnetically Induced Currents (GICs) in grounded, conducting infrastructure. These GICs can damage or degrade equipment if they are sufficiently intense—understanding and forecasting them is of critical importance. One of the key magnetospheric phenomena are Sudden Commencements (SCs). To examine the potential impact of SCs we evaluate the correlation between the measured maximum GICs and rate of change of the magnetic field (H′) in 75 power grid transformers across New Zealand between 2001 and 2020. The maximum observed H′ and GIC correlate well, with correlation coefficients (r2) around 0.7. We investigate the gradient of the relationship between H′ and GIC, finding a hot spot close to Dunedin: where a given H′ will drive the largest relative current (0.5 A nT−1 min). We observe strong intralocation variability, with the gradients varying by a factor of two or more at adjacent transformers. We find that GICs are (on average) greater if they are related to: (a) Storm Sudden Commencements (SSCs; 27% larger than Sudden Impulses, SIs); (b) SCs while New Zealand is on the dayside of the Earth (27% larger than the nightside); and (c) SCs with a predominantly East‐West magnetic field change (14% larger than North‐South equivalents). These results are attributed to the geology of New Zealand and the geometry of the power network. We extrapolate to find that transformers near Dunedin would see 2000 A or more during a theoretical extreme SC (H′ = 4000 nT min−1).