Discovery: Icy Satellites

View of Venus Faulted Volcano

Cutaway view of stresses in the lithosphere beneath a large radiating fracture system on Venus, Mbokomu Mons. Warmer colors (yellow, red) indicate high stresses at the top and bottom of the lithosphere and surrounding an inflating magma chamber at center. The red shape below the lithosphere represents a plume in the convecting mantle that pushes the lithosphere upward. This uplift creates the state of extension in the upper lithosphere that is conducive to the propagation of radial dikes from the chamber, thereby producing the radiating fractures.

Map and Modeling of 2006 Hawaiian Earthquakes

On October 15, 2006, two earthquakes shook the northwest coast of the island of Hawaii 6 minutes apart: the magnitude 6.7 Kiholo Bay event and the shallower but still unexpectedly deep magnitude 6.0 Mahukona event (see map). Their close proximity in space and time suggested a common origin, but sharp contrasts in mechanism and depth present an unusual fault/aftershock relationship. McGovern (2007) hypothesized that these "fraternal twin" earthquakes are the divergent outcomes of a single process: downward flexing of the lithosphere in response to loading by the Hawaiian volcanos Hualalai and Kohala.

Map and Modeling of 2006 Hawaiian Earthquakes

Finite element models of volcanic loading show that the initial Kiholo Bay event can be attributed to a high-stress zone in the lower lithosphere.

Map and Modeling of 2006 Hawaiian Earthquakes

However, an explanation for the depth (also within the mantle) of the Mahukona event requires models that incorporate a strong stiffness contrast between crust and mantle in order to produce peak upper lithosphere stresses at the top of the stiffer mantle's. This compressional high-stress zone also traps magma near the base of the crust, thereby explaining the seismically observed thickening from below (underplating) of Hawaiian volcanos.

Giant Volcano Landslides on Earth and Mars

A color map of topography of the island of Oahu and bathymetry of the submarine Nuuanu slide, identifying potential analogs to structures in the Olympus Mons aureole (black and white images further below).


The prominent Tuscaloosa Seamount (label 1 in color bathymetry) has dimensions very similar to large blocks in the north lobe of the Olympus Mons aureole (image b, label 1).


A close-up of the block shows lineations that resemble the raised margins of lava flows on the Olympus Mons edifice, thereby establishing a link between the block and the edifice that strongly points

Giant Volcano Landslides on Earth and Mars

A topographic rendering of the massive north aureole lobe of Olympus Mons is flanked by similar renderings for Hawaiian volcanos: the submarine Nuuanu slide north of Oahu (left) and the Hilina slump of the south flank of Kilauea volcano on the big island of Hawaii (right). The insets in the central figure show the Hawaiian examples at the same scale as Olympus Mons. The Olympus Mons north aureole is about 30 times the volume of the Nuuanu slide, comparable to the volume difference between the Olympus Mons main edifice and a Hawaiian island. However, note that the sizes of individual aureole blocks are similar to those constituting the Hawaiian landslides, suggesting that the planet-independent strength of basaltic rocks plays a role in determining block size.

Olympus Mons East Flank

Olympus Mons, the tallest volcano in the solar system at 23 km from base to summit, is located on the flank of the immense Tharsis Rise on Mars. The Olympus Mons edifice spreads outward on a deep detachment, likely rooted in phyllosilicate (clay) sediments produced in abundance in early martian history. As at Hawaii, spreading creates deformation and failure of the volcano flanks: a close-up of the eastern flank and basal escarpment of Olympus Mons shows a partially failed segment bounded by extensional faults at the top (white arrows) and compressional faults at the bottom (black arrows). If this segment were to fail completely, the resulting landslide deposit would be comparable to the volume of the aureole lobe directly east. The very young ages of local lava flows, channels (possibly water-carved), and flank deformations (less than 40 million years) suggest the existence of a warm, wet, and chemically rich subsurface environment up to the present day, making the Olympus Mons east flank a compelling astrobiological target.

Dr. Patrick McGovern's research has focused on the structure and evolution of large volcanic edifices and provinces on the terrestrial planets.

 

He approaches these problems from a quantitative mechanical perspective, calculating the immense stresses that build up in the lithosphere (mechanically strong outer layer of a planet) as a result of loads from the surface (the large volcanos themselves), the subsurface (buoyant crustal underplating and mantle plumes), and within the lithosphere (inflation of magma chambers).

 

He compares the predictions of such models to observations from imaging, topography, gravity, and spectroscopy datasets, in order to constrain the conditions (such as lithospheric thickness, magmatic supply rate, loading history, and magma chamber dimensions) that controlled the formation of a volcano.

 

Dr. Patrick McGovern

Planetary Geophysics
Patrick McGovern