July 24 - August 6, 2006
Cruise location: Vance Seamount
Chief scientists: David Clague, MBARI
Ship: R/V Western Flyer Vehicle: ROV Tiburon
Understand the formation of calderas on submarine volcanoes
Among the questions we have: How and when do calderas form? Do they form from one large, final event or are there repeated events? How big and how violent are the eruptions; how far is material ejected and how large are the particles? How deep in the volcano does the material come from? Are the explosions driven by magmatic gas or water vapor; is hydrothermal activity in any way associated?
Our first dive will be at NESCA (Northern Escanaba Trough) on the southern Gorda Ridge, which is along our transit from Moss Landing to Axial and Vance Seamounts. We will take push-cores for volcanic glass particle distribution, collect video transects across older and younger flows, and collect hydrothermal vent clams, completing studies that were the focus of dives in 2005 (see Ridges 2005 cruise logs).
Our next two dives will be at Axial Seamount on the Juan de Fuca Ridge. We will take a series of vibracores on the east and west flanks of the volcano to sample the deposits left by explosive eruptions and determine their stratigraphy and distribution.
The final dives will be on cones of the Vance Seamount Chain. We will determine the stratigraphy of the flows and explosive deposits that built the cones by collecting rocks exposed in the collapsed caldera walls, much like a geologist on land would examine rocks in road-cuts along a highway to study the geology of the region. We also will look for hydrothermal materials as active vents, in sediment cores or the alteration of rocks.
From our discoveries of particles formed from explosive fragmentation of lava we infer that explosive volcanic eruptions have occurred in many different settings in the deep sea. These include Loihi Seamount, the Hawaiian North Arch, and the Gorda and Juan de Fuca Ridges (see our website's midocean ridge explosive eruptions page and links in that page). Like Loihi off the Big Island of Hawaii, Axial Seamount on the Juan de Fuca Ridge has abundant fragmental debris at the summit and a large caldera. Many other seamounts that are deeper than Axial and Loihi also have calderas.
Axial Seamount rises to just less than 1400m below sea level (the rest of the Juan de Fuca Ridge is greater than 2400m along much of its length). It has formed due to an over-supply of magma at this one point on the ridge. In 2005 we visited Axial's summit region with the ROV Tiburon, and found that the north flank of the summit caldera was a broad expanse of coarse volcanic sand and mud that included abundant "limu o pele" (broken walls of lava bubbles), low-temperature hydrothermal clays, and broken rock fragments. This material must be ejecta from a large eruption or series of eruptions, and probably includes debris from the event that caused the summit caldera to collapse.
The Vance Seamounts are a chain of seamounts that erupted at another point along the Juan de Fuca Ridge. The volcanic cones were carried off-axis as the underlying plate grew at the ridge, forming a line of seamounts to the northwest of the ridge. With summits barely cresting 2000m depth, these volcanoes are considerably deeper than Axial Seamount. Most of the volcanoes of the Vance chain are flat-topped cones, probably due to ponding of lava at the summits during the effusive eruptions. The cones have very large, deep calderas that resulted from the collapse of large magma chambers, which themselves were due to extensive melting of the mantle below. Several calderas are nested, which suggests that there were repeated but discrete intense eruption and collapse events. We would like to know if there are deposits from explosive eruptions, as at Axial. One of the volcanoes consists of numerous small cones stacked on top of each other, forming low, broad lava domes that may be precursors to the large, round cratered volcanoes and for some reason never fully evolved. These small cones should allow us to see what the early stages of the larger volcanoes were like and if the lava compositions are different.
The Escanaba Trough is a spreading center valley that is filled by glacial sediments released through the Columbia Gorge at the end of the last glacial period. The study area has a large young lava flow around a series of uplifted hills. These hills formed when lava was injected into the sediment and uplifted it along ring faults. The site has had long-lived hydrothermal activity and several vents are still active today. We have studied the hydrothermal vent fluids and deposits, the emplacement of the lava flow, the mildly explosive eruption that fed the flow (by mapping out the distribution of small glass particles ejected into the overlying water column, see last year’s cruise log). The one thing we have not been able to determine is when the eruption took place and therefore, how long the hydrothermal system has been active. We have collected quite a few samples with this goal, but all have turned out to be in the wrong places. We think we have the right location selected now and will collect a series of cores to determine the depth in the core where the most glass particles reside. Then using known sedimentation rates, we can calculate the age. We are also going to try another approach to determine the age of the flow, by collecting the shells (tests) of small foraminifera that live on top of the flow and radiocarbon dating the carbon they use to glue together the sand grains that make up their shells.
Submarine Volcanism project pages
Explosive eruptions at a mid-ocean ridge
- Clague, D.A., A.S. Davis, J. E. Dixon (2003) Submarine strombolian eruptions on the Gorda mid-ocean ridge, In: Explosive Subaqueous Volcanism, J.D.L. White, J.L. Smellie, and D.A. Clague (eds), Geophysical Monograph 140, American Geophysical Union, 111-128
- Davis, A.S., D.A. Clague (2003) Got glass? Glass from sediment and foraminifera tests contribute clues to volcanic history, Geology, 31:(2): 103-106
- Embly, R.W., W.W. Chadwick, Jr., D. Clague, and D. Stakes (1999) 1998 eruption of Axial Volcano: multibeam anomalies and seafloor observations, Geophysical Research Letters, 26(23): 3425-3428
- MBARI mapping program: Axial Volcano
- Clague, D.A., J.R. Reynolds, and A.S. Davis (2000) Near-ridge seamount chains in the northeastern Pacific Ocean, Journal of Geophysical Research, 105(B7): 16,541-16,561
- Davis, A.S. and D.A. Clague (2000) President Jackson Seamounts, northern Gorda Ridge: tectonomagmatic relationship between on- and off-axis volcanism, Journal of Geophysical Research, 105(B12): 27,939-27,956
- MBARI mapping program: Vance Seamounts