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Grabens, or valleys formed during extensional tectonic events, are common but rarely observed during formation. In November 2023, inelastic surface deformation formed abruptly along Iceland's plate boundary in Grindavík. We documented graben formation in real‐time through satellite mapping (InSAR), seismicity, GNSS data, repeated lidar surveys, and field mapping. Five normal faults and ∼12 fissures ruptured the surface delineating two grabens separated by a horst, a context not present in other contemporary case studies. The graben normal faults slipped rapidly (over hours) and maximum surface motions coincided with the occurrence of turbulent seismic swarms in both space and time. Although 3 eruptions took place ∼15 km northeast of Grindavík from 2021 to 2023, attributed to magma intrusions (i.e., dikes), none of these also formed grabens. Thus, the Grindavík grabens shows evidence for tectonic origins. Real‐time monitoring of these phenomena provide insight into graben formation on Earth and potentially on other planets. Valleys known as grabens, typically caused by extensional tectonic events, are a common geological feature, yet their formation is rarely observed. In November 2023, such two grabens suddenly emerged along the boundary between tectonic plates in the town of Grindavík, Iceland. The grabens were shaped by tectonic activity expressed by a swarm of earthquakes and associated ground deformation and resulted in normal faults rupturing the surface and cutting through houses, linear infrastructure including water pipelines and roads within Grindavík. We document the grabens and horst in real time using satellite mapping (InSAR), geodetic GPS data, repeated drone surveys, field mapping, and seismic recordings from a local seismic network. The combination of these data provide unprecedented level of precision in characterizing surface and sub‐surface deformations, especially when maximum surface motions correlate with a turbulent seismic activity in both space and time. Critically, following the formation of the grabens, a series of intensive through short‐lived eruptions happened in December 2023, January 2024, February 2024, March, and May 2024 within the northernmost portion of the grabens. Our observations provide valuable insights into the natural laboratory of Iceland and contribute to the understanding of plate tectonics both on Earth and other planets. The 2023 seismic swarm and extension lead to a graben forming that coincides in time and space along Iceland's plate boundaryDuring 2021 to December 2023 only one tectonic graben formed, although 4 eruptions have taken placeThe graben in Grindavík, Iceland is wider at the surface than most recently documented grabens (∼4,500 m vs. <1,000 m) The 2023 seismic swarm and extension lead to a graben forming that coincides in time and space along Iceland's plate boundary During 2021 to December 2023 only one tectonic graben formed, although 4 eruptions have taken place The graben in Grindavík, Iceland is wider at the surface than most recently documented grabens (∼4,500 m vs. <1,000 m)

[Volcanic eruptions generate continuous or episodic tremor, which can provide unrivaled information about activity changes during eruption. However, the wealth of information in episodic tremor patterns is often not harvested and transitions between patterns remain obscure. The 2021 Geldingadalir eruption, Iceland, is an exceptional case, where the lava effusion caused continuous tremor, and 8698 tremor episodes spanning two orders of magnitude in duration and repose. Based on seismometer and video camera data, we associate several‐minute‐long, symmetrical episodes with an open vent system, where lava remains in the crater bowl during repose, connected to a shallow magma compartment. Ramp‐shaped episodes, lasting several hours, are associated with a temporary closure of the vent system, where no lava remains in the crater bowl during repose and more time is required to resume effusion. The transition from continuous to episodic effusion is related to the cumulative time spent in effusion and repose, and to external factors like crater wall collapses. The range of observed eruption styles and shifts between them, took place at unchanged magma supply rate. This underpins the importance of processes, geometry and evolution of the shallow conduit with time.] Volcanic eruptions can provide unrivaled information about the subsurface structure and processes driving it. Often effusion happens continuous over a time span. However, sometimes the effusion starts and stops and is hence episodic. During the 2021 Geldingadalir eruption, Iceland the lava flowed continuously from the vent but later stopped 8698 times. Some of these episodes where a few minutes long, while others lasted several hours. We interpret several‐minute‐long episodes as an open system, where lava remains in the crater during repose. This system can restart fast and easy. During several hour‐long episodes, no lava remains in the crater during repose. The system needs more time to reopen the vent. The system also reacts depending on the time it is in repose or effusion. And finally, external factors like crater wall collapses modify the episodic pattern. The most interesting feature is the range of eruption styles and transitions between them, that occurred at constant magma inflow rate and are hence caused by the shallow conduit. The 2021 Geldingadalir eruption, Iceland, featured 8698 tremor episodes of minute to week durationAn open vent system with lava residing in the crater during repose featured minute‐long lava effusion with bell‐ or rectangle‐shaped tremorA semi‐closed vent system with no lava residing in the crater featured hour‐long lava effusion with ramp‐shaped tremor The 2021 Geldingadalir eruption, Iceland, featured 8698 tremor episodes of minute to week duration An open vent system with lava residing in the crater during repose featured minute‐long lava effusion with bell‐ or rectangle‐shaped tremor A semi‐closed vent system with no lava residing in the crater featured hour‐long lava effusion with ramp‐shaped tremor

The slow spreading Reykjanes Ridge overlies the Iceland hotspot and has undergone well ordered changes in crustal segmentation. Previous studies have attributed these changes to varying mantle plume thermal effects, rendering the lithosphere ductile or brittle. Here we use seafloor spreading magnetic anomalies to show that crustal accretion has been focused throughout its spreading history and to determine the detailed evolution of Reykjanes Ridge segments. By ∼53 Ma, organized spreading had developed on an orthogonally spreading linear axis following continental breakup. After a plate motion change at ∼38 Ma, orthogonally spreading offset ridge segments formed by ridge propagation forming varying length fracture zones. From then to the present, the offset segments diachronously migrated back to the original linear geometry from north to south replacing orthogonal with oblique spreading as the axis became linear again. Fracture zones were not terminated, however, simply by reducing segment offsets even to zero. Their termination involved the axial propagation of buoyant upwelling instabilities across the discontinuities, correspondingly extending V‐shaped crustal ridges southward. This evolution was guided by a persistent linear deep damp mantle melting interval maintained by the episodic propagation of buoyant upwelling instabilities. Our study indicates that at slow spreading ridges, where buoyant upwelling instabilities govern crustal segmentation, spatial gradients in mantle melting properties may direct the behavior of the instabilities. Where ridges overlie regional hotspot gradients in mantle melting, buoyant instabilities may propagate systematically, and plate boundary evolution may follow an organized pattern. As the Reykjanes Ridge overlies the Iceland hotspot, much of its evolution has been proposed to reflect varying mantle plume thermal effects. Here we use seafloor spreading magnetic lineations to study this evolution and better understand controlling mechanisms. We find that typical plate tectonic processes can account for the evolution without resorting to changing mantle plume thermal effects. However, a persistent regional gradient in mantle melting associated with the Iceland hotspot strongly directs the evolution. The ridge originated as a linear axis. It became fragmented by rift propagation following a plate motion change. The offset segments then progressively reassembled their original linear geometry by asymmetric spreading. Axial propagation of buoyant upwelling instabilities terminated fracture zones when segment offsets became small. This evolution was guided by a deep zone of mantle melting that remained linear, maintained by axially propagating buoyant instabilities that also form V‐shaped crustal ridge on the ridge flanks. Our study indicates that at slow spreading ridges where buoyant mantle upwellings govern crustal segmentation, factors that influence mantle melting can direct the motion of the instabilities. Where hotspots form pronounced along‐axis melting gradients, buoyant upwelling centers and crustal segmentation can follow an organized evolution. Overlying the Iceland hotspot, the Reykjanes Ridge underwent a remarkably organized plate boundary evolutionThe linear ridge became fragmented following a plate motion change then systematically reassembled its original linear configurationThe Iceland hotspot melting gradient causes buoyant mantle upwelling cells to propagate, reestablishing the original linear axis Overlying the Iceland hotspot, the Reykjanes Ridge underwent a remarkably organized plate boundary evolution The linear ridge became fragmented following a plate motion change then systematically reassembled its original linear configuration The Iceland hotspot melting gradient causes buoyant mantle upwelling cells to propagate, reestablishing the original linear axis

A large rockslide was released from the inner Askja caldera into Lake Askja, Iceland, on 21 July 2014. Upon entering the lake, it caused a large tsunami that traveled about ~3 km across the lake and inundated the shore with vertical runup measuring up to 60–80 m. Following the event, comprehensive field data were collected, including GPS measurements of the inundation and multibeam echo soundings of the lake bathymetry. Using this exhaustive data set, numerical modeling of the tsunami has been conducted using both a nonlinear shallow water model and a Boussinesq-type model that includes frequency dispersion. To constrain unknown landslide parameters, a global optimization algorithm, Differential Evolution, was employed, resulting in a parameter set that minimized the deviation from measured inundation. The tsunami model of Lake Askja is the first example where we have been able to utilize field data to show that frequency dispersion is needed to explain the tsunami wave radiation pattern and that shallow water theory falls short. We were able to fit the trend in tsunami runup observations around the entire lake using the Boussinesq model. In contrast, the shallow water model gave a different runup pattern and produced pronounced offsets in certain areas. The well-documented Lake Askja tsunami thus provided a unique opportunity to explore and capture the essential physics of landslide tsunami generation and propagation through numerical modeling. Moreover, the study of the event is important because this dispersive nature is likely to occur for other subaerial impact tsunamis. Unique field data set on joint landslide deposit and tsunami runup presentedFirst model to show that frequency dispersion is needed to closely reproduce runup field dataOptimization procedure used to retrofit the likely landslide dynamics

The 2014–2015 Bárðarbunga‐Veiðivötn fissure eruption at Holuhraun produced about 1.5 km3of lava, making it the largest eruption in Iceland in more than 200 years. Over the course of the eruption, daily volcanic sulfur dioxide (SO2) emissions exceeded daily SO2emissions from all anthropogenic sources in Europe in 2010 by at least a factor of 3. We present surface air quality observations from across Northern Europe together with satellite remote sensing data and model simulations of volcanic SO2for September 2014. We show that volcanic SO2was transported in the lowermost troposphere over long distances and detected by air quality monitoring stations up to 2750 km away from the source. Using retrievals from the Ozone Monitoring Instrument (OMI) and the Infrared Atmospheric Sounding Interferometer (IASI), we calculate an average daily SO2mass burden of 99 ± 49 kilotons (kt) of SO2from OMI and 61 ± 18 kt of SO2from IASI for September 2014. This volcanic burden is at least a factor of 2 greater than the average SO2mass burden between 2007 and 2009 due to anthropogenic emissions from the whole of Europe. Combining the observational data with model simulations using the United Kingdom Met Office's Numerical Atmospheric‐dispersion Modelling Environment model, we are able to constrain SO2emission rates to up to 120 kilotons per day (kt/d) during early September 2014, followed by a decrease to 20–60 kt/d between 6 and 22 September 2014, followed by a renewed increase to 60–120 kt/d until the end of September 2014. Based on these fluxes, we estimate that the eruption emitted a total of 2.0 ± 0.6 Tg of SO2during September 2014, in good agreement with ground‐based remote sensing and petrological estimates. Although satellite‐derived and model‐simulated vertical column densities of SO2agree well, the model simulations are biased low by up to a factor of 8 when compared to surface observations of volcanic SO2on 6–7 September 2014 in Ireland. These biases are mainly due to relatively small horizontal and vertical positional errors in the simulations of the volcanic plume occurring over transport distances of thousands of kilometers. Although the volcanic air pollution episodes were transient and lava‐dominated volcanic eruptions are sporadic events, the observations suggest that (i) during an eruption, volcanic SO2measurements should be assimilated for near real‐time air quality forecasting and (ii) existing air quality monitoring networks should be retained or extended to monitor SO2and other volcanic pollutants. The 2014–2015 Icelandic fissure eruption at Bárðarbunga affected air quality in far fieldSatellite‐derived average daily SO2burden of 99 ± 49 kt (OMI) and 61 ± 18 kt (IASI) in September 2014We calculate a total release of 2.0 ± 0.6 Tg of SO2for September 2014 and fluxes up to 120 kt/d

The 2011 eruption of a 20-km-high volcanic plume from Grímsvötn Volcano, Iceland, led to the closure of northern European airspace. Geodetic measurements from the volcano reveal a correlation between plume height, surface deformation and magma-chamber pressure, with a delay of an hour, implying that volcanic-plume behaviour can be predicted before eruption onset.

Between 24 March and 5 June 2010, the Hyperion hyperspectral imager and Advanced Land Imager (ALI) on NASA's Earth Observing 1(EO-1) spacecraft obtained an unprecedented sequence of 50 observation pairs of the eruptions at Fimmvörðuháls and Eyjafjallajökull, Iceland. This high acquisition rate was possible only through the use of data flow streamlined by using the autonomously operating NASA Volcano Sensor Web (VSW). The VSW incorporates notifications of volcanic activity from multiple sources to retask EO-1and process Hyperion data to extract eruption parameters from high spatial and spectral resolution visible and short-wavelength infrared data. Physical changes in eruption style and magnitude were charted as the eruptions ran their course. Rapid data downlink and automatic data-processing algorithms generated a variety of products which are compared with estimates from ground-based observations and post-eruption in situ measurements. Estimates of effusion rate from heat loss measurements underestimate actual effusion rate (while still following broad eruption rate trends) but are closer to in situ estimates for effusive eruptions (Fimmvörðuháls) than explosive, ash-rich eruptions (Eyjafjallajökull). During the later stages of the 2010 eruption, VSW-generated products were rapidly delivered to end-users in Iceland to aid in the assessment of risk and hazard. The success of the VSW led to Icelandic Meteorological Office (IMO) in situ sensors being incorporated into the VSW, and in May 2011 an IMO seismic alert autonomously triggered EO-1observations of a new eruption at Grímsvötn volcano. Finally, the VSW demonstrates an autonomy-driven, multi-asset, spacecraft retasking and data processing system that maximizes science return, a desirable capability for future NASA missions. An autonomous sensor web observed the 2010 Eyjafjallajokull eruptionsHyperion revealed the waxing and waning of activity during two eruptionsEffusion rates were underestimated but broadly followed actual activity

Volcanic hazards from Pico de Orizaba volcano are presented here tor the first time. Some 1.3 million people live within the hazard zone, which in the most severe case would encompass the Mexican Gulf coast, east of the volcano. Three major cities located in the eastern part of the hazard zone account for 800 000 of this population and about 200 000 people live within a 20 km radius of the volcano. Probability calculations are presented as an attempt to quantify the hazards in the surroundings of the volcano. Such quantification can be of use in planning for future land use within the hazard zones.