Geology topics

D. Sarah Stamps

Publications and source records attributed to D. Sarah Stamps.

6 recordsLinked to original sources

USGS2026

Inflation at Ol Doinyo Lengai driven by shallow magma intrusion during the 2022–2023 uplift episode in an early-phase continental rift

The active stratovolcano Ol Doinyo Lengai is located in the magma-rich, early-phase continental Natron Rift, which is part of the larger East African Rift System. Since 2016, a geodetic network comprising 7 Global Navigation Satellite Navigation (GNSS) and 2 seismic stations has been deployed to monitor inflation and deflation around this volcano. Between March 2022 and August 2023, millimeter-precision GNSS data detected a non-eruptive uplift episode at Ol Doinyo Lengai. In this work, we explore potential drivers of the uplift event by inverting GNSS data using the open-source software package dMODELS developed by the US Geological Survey. We assess four mathematical models (spherical, sill-like, spheroid, dislocation/dike) and find the best-fit solution is consistent with an intrusion of magma from a shallow, sill-like source at approximately 3.1 ± 2.2 km depth below the summit with a volume change of 0.99 ± 0.22 × 10 6 m 3 . Although continuous GNSS observations of surface motions at Ol Doinyo Lengai are relatively short, having only begun in 2016, this work contributes to our understanding of the ongoing magmatic processes and its long-term deformation cycle, allowing for improved volcanic hazards assessment and comparisons with global volcanic systems.

Ol Doinyo Lengai↗

USGS2026

dMODELS, a MATLAB software package for modeling crustal deformation near volcanic centers and active faults using Global Navigation Satellite System data—User guide

dMODELS is a MATLAB software package that implements the most common analytical models used to interpret deformation measurements near faults and active volcanic centers. This manual focuses on inversion of deformation data from the Global Navigation Satellite System (GNSS). The included case studies emphasize the GNSS inversion component of the software. Source models include pressurized spherical, spheroidal, and horizontal sill (penny-crack) magma reservoirs in a homogeneous, elastic, isotropic, flat half-space. A topography correction is available for the spherical source. Dikes and faults are described following the mathematical notation for the rectangular dislocations in a homogeneous, elastic, flat half-space. Equations have been reviewed for typographical errors present in the original literature and verified against finite-element method numerical models. GNSS data from the 2006 eruption at Augustine Volcano, Alaska; the 1998–2000 unrest at Taal Volcano, Philippines; and the 2009 earthquake in L’Aquila, Italy, are used to demonstrate the application of the software package.

Techniques and Methods↗

USGS2026

Role of volcano-tectonic interactions during early-phase magma-assisted continental rifting

We study volcanic-tectonic interactions during the early phase of rifting in the Natron Rift, a magmatic segment of the East African Rift System. We use the open-source crustal deformation modeling code, PyLith, to model deflation during the 2007–2008 explosive eruptions and inflation during 2016–2023. We compare predictions of surface displacements resulting from magma reservoir inflation from 3D models with and without topography and homogeneous and heterogeneous material properties against Global Navigation Satellite System displacements from 2016 to 2023. We prefer the model with heterogeneous material properties and topography for fitting the observed displacements. Including topography improves the fit to GNSS data and modulates stress changes from shallow magma sources. Our numerical modeling of Coulomb stress changes suggests that deflation of a magma reservoir under the active Ol Doinyo Lengai volcano could trigger oblique normal slip on the Natron Fault with Coulomb stress increases exceeding ∼0.1 MPa on the volcano-adjacent fault segment. Fault slip on the Natron Fault is less likely during inflation of the magma reservoir because normal compressive stress increases on the fault. We also demonstrate that Coulomb stress changes are sensitive to the inclusion of topography in our model, particularly because the depth of the magma reservoir is similar to the amplitude of the topographic relief.

Ol Doinyo Lenga↗

USGS2025

Present-day vertical land motions (VLM) of the Chesapeake Bay region derived from robust network imaging of global navigation satellite system (GNSS) observations

The Chesapeake Bay region (defined as longitudes − 78° to -74° and latitudes 36.5° to 40°) experiences the highest rates of relative sea-level rise (RSLR) on the Atlantic Coast. Regional land subsidence influences RSLR, however quantified rates of vertical land motions (VLM) are inconsistent in published solutions. For 5 years from 2019 to 2023, new Global Navigation Satellite System (GNSS) campaign data were collected at over 60 sites across the Chesapeake Bay region annually. These data were processed and combined with continuous GNSS data (120 stations) from the region covering the same time-period using GAMIT-GLOBK to produce 3D velocities and their associated uncertainties. We use the Robust Network Imaging algorithm to interpolate GNSS-derived VLM to produce a new regional VLM solution of the Chesapeake Bay region. We find that land subsidence is ubiquitous throughout the region with rates varying from − 2.97 to -0.40 mm/yr. In major cities across the Chesapeake Bay region, VLM rates are − 1.1 ± 1.6 mm/yr (1-sigma) for Washington DC, -0.8 ± 1.4 mm/yr for Baltimore, MD, -2.4 ± 0.5 mm/yr for Ocean City, MD, and − 2.3 ± 1.0 mm/yr for Hampton, VA. When we compare our VLM rates with a geodetic-based solution from 1974, we observe meaningful shifts in the locations and rates of maximum subsidence. The results of this work underscore that regular monitoring of VLM and can be used to improve projections of relative sea-level changes as well as the associated coastal hazards for communities in the Chesapeake Bay region.

Delaware, Maryland, New Jeresy, Pennsylvania, Virg↗

USGS2023

Elucidating the magma plumbing system of Ol Doinyo Lengai (Natron Rift, Tanzania) Using satellite geodesy and numerical modeling

Ol Doinyo Lengai, located in the southern Eastern Branch of the East African Rift had several eruptive episodes with ash falls and lava flows (VEI 3) that caused damage to the nearby communities between 2007 and 2010. The volcano is remote and access is difficult. Although this volcano has been studied for decades, its plumbing system is still poorly understood, in part, because of the lack of precise observations of surface deformation during periods of quiet and unrest. This study investigates the volcanic plumbing system of Ol Doinyo Lengai and its surroundings using data from the network of permanent Global Navigation Satellite System (GNSS) sites monitoring the volcano (the TZVOLCANO network) around the flanks of the volcano and Interferometric Synthetic Aperture Radar (InSAR) observations. We constrain surface motions using 6 GNSS sites distributed around Ol Doinyo Lengai, operating between 2016 and 2021, and InSAR data covering nearly the same time period. Because of the complex local tectonics, the interpretation of the deformation pattern is not straightforward. We first invert the GNSS deformation and InSAR observations independently to infer potential deformation sources. Then we perform a joint inversion of both GNSS and InSAR datasets to verify our findings. We compare the results from the joint inversion with the results from inverting each dataset independently. The GNSS, InSAR, and joint inversion results point to a deflating source, located east of Ol Doinyo Lengai and southwest of the dormant volcano Gelai at a depth of 3.49 ± 0.03 km (GNSS inversion), 5.2 ± 1.2 km (InSAR inversion) and 3.49 ± 0.06 km (joint inversion) relative to the summit (vent) and with a volume change ∆V of −0.04 ± 0.05 × 10 6 m 3 (GNSS inversion), −0.39 ± 0.29 × 10 6 m 3 (InSAR inversion), and − 0.04 ± 0.01 × 10 6 m 3 (joint inversion). Although this is non-unique modeling of geodetic datasets with small signals, the inversion results suggest that Ol Doinyo Lengai could be fed by an offset multi-reservoir system that includes a shallow magma reservoir (<5 km) east of Ol Doinyo Lengai, possibly connected to a deeper magma reservoir.

Natron Rift, Ol Doinyo Lengai↗

USGS2022

GPS data from 2019 and 2020 campaigns in the Chesapeake Bay region towards quantifying vertical land motions

The Chesapeake Bay is a region along the eastern coast of the United States where sea-level rise is confounded with poorly resolved rates of land subsidence, thus new constraints on vertical land motions (VLM) in the region are warranted. In this paper, we provide a description of two campaign-style Global Positioning System (GPS) datasets, explain the methods used in data collection and validation, and present the experiment designed to quantify a new baseline of VLM in the Chesapeake Bay region of eastern North America. Data from GPS campaigns in 2019 and 2020 are presented as ASCII RINEX2.11 files and logsheets for each observation from the campaigns. Data were quality checked using the open-source program TEQC, resulting in average multipath 1 and 2 values of 0.68 and 0.57, respectively. All data are archived and publicly available for open access at the geodesy facility UNAVCO to abide by Findable, Accessible, Interoperable, Reusable (FAIR) data principles.

Chesapeake Bay area↗