1) First of all, I wanted to plug our cruise
website:
I probably should have done this a
while ago, but for those who are interested in more details on the cruise
mission, progress, and perspectives from some of the other people onboard, feel
free to check it out. I wrote the
section on “Tools/Methods,” which is a more technical (but still accessible for
most people) explanation of the instruments we are using, including some
background on the Earth’s magnetic field, gravity, sonar systems, and some of
the steps in the data processing.
This is covered to a lesser degree in my previous post on the Scientific
Mission, but if you want more details, check it out. For any geologist-types reading this, there is also a link to the proposal for the project, which will give you all of the details and background you could possibly want.
2) I apologize in advance for the following rant: we have ~9 days left until the cruise is over
(we added one more day and now are returning on 9/15), and I
definitely have a full-on case of boat fever. Hawaii may be a small place relative to the mainland, but in
comparison this boat is beginning to feel like a floating prison. I’m ready to be back home, I’m ready
for an end to the constant ship noise, the constant motion, the extremely
repetitive daily routine, and an internet connection that doesn’t crash every 5
minutes. I also miss fresh fruits
and veggies, which ran out long ago.
Not having a single good night of sleep for almost a month does not help
much either. At this point, I’m
pretty much a robot going through the motions, each day is almost exactly
identical to the next. Part of
that is the nature of a mapping cruise, we don’t have any deck work to break up
the monotony of staring at computer screens, and our daily duties do not vary
at all. I still find some pleasure
in going outside, getting fresh air, and staring out at the endless ocean (when
it’s not wet and gray like today), but even that is starting to lose its appeal
after the 20th time. I
still have yet to see any more sea life than a few whale spouts off in the
distance, and I’ve only seen a total of ~10 stars and 2 sunsets. Although I did get tired of dredging
after a while on our cruise south of Samoa, I would love to actually see some
rocks and do something different for once. It never takes me more than 3 hours of my 8 hour shift to
finish processing all of the data for the day, so I have been doing a lot of
reading lately (528 pages over the last two days) to pass the time. I’m not entirely alone in these
feelings, everyone is usually starting to get antsy and pretty much ready to be home at this point in the
cruise, when the end is in sight but still seems so far away. I’m trying to stay positive and take it
one day at a time, but it’s getting increasingly difficult.
3) After that rant, I feel I should balance it with
a few positive thoughts and some perspective. In
general, being on the ship for so long and stuck in this repetitive routine helps
me appreciate my life in Hawaii a lot more and realize how lucky I am. Although it may be boring and feel
repetitive at times sitting in my office and reading/writing papers, processing
data, etc., I at least have nights and weekends mostly free to explore the
beautiful place I live in, swim in the ocean, hang out with an awesome group of
friends, and sleep in a bed that is more than 3” wider on either side than me. Not to mention fresh delicious food (and
beer!), and much more. Plus, I do
get paid to travel to exotic places all over the world, even if I’m only on
land for a few days, so I can’t complain too much.
In a broader sense, it helps to focus on the fact that no matter how
boring and repetitive life on the ship can be, I still have a better life than
~90+% of people in the world. It’s
petty to complain about not having fresh fruits and veggies when I have free
meals that I don’t have to clean up after, snacks and ice cream available at
any time, a roof (of a sort) over my head, a place to sleep, and money coming into my bank
account. There are millions of
people in the world that don’t even know if they’re going to eat anything today
and would gladly take the scraps that I scrape off my plate, millions more that
live in constant fear and oppression, and even in our comparatively safe and
affluent society, there are still those who do not have the luxury of steady
income and who struggle more than I can possibly imagine just to live day to
day. This is something I always
try to remember whenever I complain about some comparatively minor annoyance in
my life, but it can be easy to forget and get caught up in your own problems
and daily worries.
4) Another positive aspect is that the science is
getting more interesting as we cover more of the survey area. While we haven’t necessarily seen slam-dunk
evidence proving either of the theories, there have been some interesting and
mysterious features showing up that we are having difficulty explaining. The best and most challenging part of
science (for me) is not the data collection or processing, it’s the
interpretation. The main reason I
became a geologist is because I enjoy thinking about how the Earth works and
trying to understand the processes that form the features that we see. It’s like being a detective trying to
solve the mysteries of the Earth.
 |
| Bathymetry map of the survey area so far. Close up plot area outlined in red, Bight fracture zone labeled. |
One interesting feature which may
point toward the pulsing plume model is at the southern end of the Reykjanes
Ridge, just north of the Bight Fracture zone (which marks the southern end of
the Reykjanes Ridge and the return to the normal stair-step pattern seen along
the Mid-Atlantic Ridge to the south), it seems that the magmatic production at
the spreading center and the crustal thickness have abruptly and dramatically
decreased. The off-axis crust
looks consistently very magmatic, it reaches depths shallower than 1000 m, and
looks like it was produced by abundant volcanic activity (as opposed to
tectonic stretching and faulting).
This fabric (which we can assume is associated with relatively thick
crust) extends for over 50 km on either side of the axis, suggesting that it
has been in this mode for an extended period of time. Then, just a few km away from the active axis, there is an
extremely sharp drop to ~2500 m deep on average, and the axis doesn’t look to
be nearly as volcanically active.
This huge change could potentially be explained by a pulse in the plume
under Iceland, which would have created the shallow off-axis crust, and after
the pulse ended, the less volcanically active axis began to form with deeper,
thinner crust. I don’t quite buy
that theory or the idea that plumes actually pulse (there is no known process
that would drive the pulsation), but it seems to superficially fit the pulsing
plume model better than the propagating rift model.
Another mysterious feature is that the seafloor on the north side of the Bight Fracture Zone is much shallower than on the south side, and the transition is again extremely abrupt. Near the spreading axis, you can clearly see that the fracture zone is basically defined by an extremely sharp boundary (essentially a single fault) that separates the crust formed along each of the active spreading segments, which are offset by ~20 km. (Remember that fracture zones form where there is a lateral offset in the spreading axis). Within ~30-40 km of the southern segment, the seafloor looks relatively similar to the seafloor north of the fracture zone, but as you get further off-axis, there is a very abrupt drop of ~500-1000 m across the fracture zone trace. At this point, we don’t really even have a theory for why this abrupt drop occurs, it doesn’t fit in with either model, and it is not a normal feature of fracture zones. Typically, spreading centers get deeper toward a fracture zone on both sides because magma production wanes toward the ends of the segments.
 |
| Close up view of the Bight Fracture Zone. Rough locations of spreading segment are marked with black lines, Bight fracture zone marked a solid red line, unnamed fracture zone to the north marked with dashed red line. In the upper-right corner, you can see the abrupt change in depth just a few km away from the axis. Some of this change in depth is due to isostatic adjustment as the lithosphere cools and thickens away from the spreading center, but that doesn't quite account for the magnitude and abrupt nature of the change. Also, as you go from north of the fracture zone to south of the fracture zone, you can see a very sharp change in depth as well. We would normally expect both sides to look more similar to the south side. Another interesting feature in this plot is that the fracture zone to the north is in the process of being erased, you can see the volcanic ridges marking the spreading segments beginning to cross the fracture zone trace and starting to take on the overlapping geometry that is ubiquitous to the north. The Bight fracture zone to the south is still fully intact and can be traced continuously across. |
