Gregg Lab Research

Triggering Eruption of Large Silicic Volcanic Systems

Posted on 08.25.2015 | Read More
Photo from the May 18, 1980 Mt. St. Helen’s eruption in Washington State (usgs.gov). The 1980 eruption  of Mt. St. Helens was a little over 1 cubic km of eruptive volume, yet had a significant impact in the region (e.g., 57 human fatalities, 12 million salmon and more than 7000 large game lost).  In comparison, the Huckleberry ridge eruption in Yellowstone (~ 2 Mya) erupted over 2000 cubic km, which makes Mt. St. Helens 1980 look tiny.

Throughout Earth’s history, there are records of very large eruptions, sometimes referred to as “supervolcanic eruptions” (depending on who you ask!). These eruptions, which are > 500 cubic km (or more than 500 times the size of Mt. St. Helens) have a severe impact on not only the region where the eruption occurs, but also across the globe. Ash clouds from eruptions of this size cover the Earth and can have a lasting effect on global climate. Understanding how and why these eruptions occur is not only import for assessing and mitigating current hazards at smaller systems, but also for understanding the evolution of volcanic systems in general.

Observations of precursory deformation during volcanic crises

Posted on 08.25.2015 | Read More
Inflation of six volcanoes revealed by an averaged 2006-2009 ground velocity map of west Sunda, Indonesia, from ALOS InSAR. Positive velocity (red colors) represents movement towards the satellite (inflation). Insets: zoom into the six inflating volcanoes. Three erupted (Sinabung, Kerinci and Slamet). From Chaussard & Amelung [2012].

Breakthrough technological advances in the form of near-real time geodetic observations from Interferometric synthetic aperture radar (InSAR) can provide critical early warning of volcanic activity. Eruptions are typically preceded by the ascent of new magma to shallow storage levels, resulting in swelling of the ground surface, which is observable with satellites. However, there are only few examples in which InSAR contributed to crises assessment, largely because not enough observations were available, because the interpretation of inflation in terms of eruption potential was ambiguous, and because it was difficult to resolve small changes because of the InSAR noise.

Interdisciplinary Studies of the 8° 20'N Seamount Chain, EPR

Posted on 08.25.2015 | Read More
Map of the East Pacific Rise between the Clipperton and Siqueiros Transform Faults showing the location of the 8 20’ Seamounts. We will be conducting a field experiment here in the winter of 2016 to better understand crustal accretion at mid-ocean ridges.

Understanding how melts are generated and focused across hundreds of kilometers through the upper mantle to the narrow mid-ocean ridge (MOR) axis is fundamental to understanding how most of Earth’s lithosphere is formed. Significant advancements have been made in the use of geodynamic models to investigate mantle melting and melt transport in 3D. However, the lack of comprehensive off-axis geophysical and correlative geochemical data presents a critical information gap that needs to be filled before progress can be made in refining these models. 

3D melt transport and crustal accretion at mid-ocean ridges

Posted on 08.25.2015 | Read More
Model output showing the depth to the top of a melt surface for a model of a segmented oceanic transform fault. The plate boundary is indicated by the white line. Black arrows show melt migration pathways and illustrate how melt formed in the mantle will flow either to the ridge or into the transform fault, where it will be erupted.

The process of generating melt beneath mid-ocean ridges becomes inherently more complex in the vicinity of transform fault offsets. Melt generation within the mantle beneath mid-ocean ridges is generally thought as a relatively two dimensional process that is a function of spreading rate. As the mantle rises beneath mid-ocean ridges, the pressure decreases and this triggers the onset of melting (i.e., decompression melting). Once the melt is generated and there is enough of it present, it will begin to coalesce and form pathways so it can continue to move up towards the spreading center. How much melt is generated and where it is generated within the mantle is a function of the thermal structure (and/or spreading rate) and starting composition.

Gravity structure of segmented oceanic transform faults

Posted on 08.25.2015 | Read More
Conceptual diagram to illustrate the processes, which may contribute to the gravity anomalies observed at intermediate and fast-slipping transform faults. Some processes include: intra-transform volcanism, propagation of dikes from nearby ridge axis, hydrothermal alteration, and variations in porosity.

Analysis of gravity from transform faults across the globe indicates that there may be a spreading rate dependence on the crustal structure of transform faults. Using a combination of three-dimensional mantle flow and thermal models and satellite gravity analyses, we found that as spreading rate increases to intermediate spreading rates, transform faults appear to have thickened crust. As this was a very strange finding, I also ran a variety of 2D forward gravity models to try to figure out what processes were impacting the gravity signal we observed. We explored a variety of possibilities including porosity variations, serpentinization, variations in thermal expansion, variations in thermal structure, etc, and found that the easiest way to produce the anomalies we observed is by overall thickening of the crust. 

Earthquake Triggering at Oceanic Transform Faults

Posted on 08.25.2015 | Read More
Modified USGS Map illustrating the mid-ocean ridge system. Dark lines are oceanic transform faults. Oceanic transform faults have a large effect on how new crust is formed and also affects spreading at mid-ocean ridges.

Three-fifths of the Earth’s surface is comprised of oceanic crust, all of which has been formed at mid-ocean ridges. The mid-ocean ridge system on Earth, is often compared to the seams of a baseball wrapping around the planet. One of the most ubiquitous features along the ridge system are the transform fault offsets, which, in our baseball analogy, are the stitches. There are more then 150 transform fault offsets around the world, but as the majority are thousands of meters beneath under water, only a handful have been studied in detail.