I successfully passed my defense on Oct. 17th, and had a wonderful celebration with many friends and family. I expect to receive my Ph.D. in several weeks, after completing revisions to my dissertation. Many thanks to all those who supported me from near and far during this exciting time!
I’ll be defending my Ph.D. dissertation in just two weeks–on Thursday, October 17th, at 8:30 am, in the Elvey Auditorium of the Geophysical Institute at UAF. My title is “Seismicity, seawater and seasonality: new insights into iceberg calving from Yahtse Glacier, Alaska.”
During my talk, I’ll describe some of the new things my advisers, collaborators and I have learned about iceberg calving by studying glacier seismicity and the fjord water properties at Yahtse Glacier in southern Alaska. Some highlights: The implosion of huge air bubbles in the fjord after iceberg calving produces icequakes detected hundreds of miles from the glacier terminus! Seawater in front of Yahtse reaches over 50 degrees F and can melt the glacier front at over 30 feet per day! Glacier termini are delicate– variations in the tides trigger variations in the rate of iceberg calving. But when the seawater is coldest in winter, very few icebergs fall into the fjord!
All of this helps us better understand one of the really major ways in which huge glaciers lose ice, and track iceberg calving remotely and automatically. So many thanks to my family, friends and coworkers who have helped to make this work happen.
I hope to see you there if you can make it!
My friend, Bob McNabb, has written a summary of the paper Chris Larsen, Shad O’Neel, and I just published in Earth and Planetary Science Letters. You can read Bob’s review here.
In his summary, Bob describes some of the more significant results of our work and how these results affect our understanding of the behavior of ocean-ending glaciers. The full paper, in which we describe our observations and calculations of the ocean’s melting of the below-sea-level glacier terminus, is posted here. Bob is a post-doctoral researcher in glaciology at the University of Alaska Fairbanks, where he studies tidewater glaciers.
The Yahtse Glacier Project’s latest study will be published in the journal Earth and Planetary Science Letters.
In this study, Chris Larsen, Shad O’Neel and I show that melting below the sea surface can control the rate at which ice is lost from Yahtse Glacier’s toe. We estimate that warm ocean water melts back the submarine terminus at over 9 meters per day, and may reasonably equal 17 m/d. 17 m/d is the rate at which ice flows into the terminus region. Thus, during our observation period, any ice fracturing off the end of the glacier terminus (iceberg calving) may be the result of an iceberg having its foundation melted out from beneath it.
We also found that our late July measurements are fairly typical from an annual perspective. In September, when the ocean water is warmer and the amount of melt and rain water released at the glacier terminus is greater, we expect that submarine melt are even greater than the rates we report.
The accepted pre-print is available here.
We’re mid-way through 2.5 weeks of work at three adjacent ocean-terminating outlets of the Greenland Ice Sheet and our project is off to a great start.
I’m presently working with researchers from the Univ of Texas at Austin and the Univ of Kansas to try and understand why three adjacent glaciers on the northern west coast of Greenland have behaved so differently over the last decade. I’m leading the seismic component of our project- other team members are heading up the deployment of GPS receivers, weather stations, and the collection of a broad suite of oceanographic measurements. Our work is based out of Uummannak, a beautiful town with very friendly people at the foot of a jagged mountain. The water offshore is full of enormous icebergs and the far walls of the fjords consist of 4000′ cliffs. The town and its surroundings are an amazing place to work.
Our hard work and the early efforts by the lead scientists who got this work funded will really pay off next year when we recover the data that will be collected for us between now and then. In the mean time, my hard work will continue in Alaska when I return in mid-August to continue my research on Yahtse Glacier and complete my Ph.D.
While standing between streams of glacier meltwater, I lectured to our undergraduate students on the importance of liquid water on glacier motion, and how rapidly the link between hydrology and basal sliding can change. Afterwards, we hiked up into the alpine tundra for an overview of Kennicott Glacier, Hidden Creek Lake, and Mt. Blackburn, the 5th tallest mountain in the US. From that overlook, we discussed the 2008 Nature Geoscience paper that I published following fieldwork at this site.
I find this teaching to be great fun, and our students are consistently excited to learn about the spectacular landscape through which we’re traveling. The gorgeous weather we enjoyed certainly didn’t hurt anything! This was my 7th straight year of teaching in Alaska’s Wrangell Mountains.
I will be co-convening topical sessions on Ice-Ocean-Sediment Interactions and Seismicity of the Cryosphere.
My co-conveners for the Ice-Ocean-Sediment Interactions session (session OS010) are Katie Boldt (Univ. of Wash.), Carlos Moffat (Univ. of Concepcion, Chile), and Martin Truffer (Univ. of Alaska Fairbanks). In this session, we’ll be exploring how glaciers, the ocean, and sediment on the seafloor and glacier bed interact to control glacier flow, iceberg calving and melt of the submarine portion of glacier termini.
For the Seismicity of the Cryosphere (C027), my co-convener is Brad Lipovsky (Stanford). In this session, presentations will focus on how seismic waves (like those produced by earthquakes) can be studied to learn more about how the frozen earth works. Topics will include iceberg calving, sea ice and river ice fracture and grinding, water motion through ice, and friction between glaciers and the ground they move over.
You can read the descriptions for these two sessions here. The AGU Fall Meeting takes place each December in San Francisco.
The national morning show has produced a short video segment describing UAF’s aerial surveying of Alaska’s glaciers.
During the glacier surveying work I described in my last post (June 3rd), our UAF team was joined by the TODAY show. They put together this story, which aired nationally on Sunday, June 9th.
In late May, I traveled to southeast Alaska as part of a team measuring the changing size of Alaska’s glaciers.
The vast majority of Alaska’s glaciers are getting smaller. There is significant on-the-ground, geological evidence for this and in-depth studies of individual glaciers have told a consistent story of diminishing ice. However, Alaska’s glaciers are found in at least 10 separate mountain ranges that span an extreme range of climates. Measuring how quickly all these glaciers are changing size, and quantifying their effect on sea level rise, is impossible from the ground.
My graduate supervisor, Chris Larsen, as well as Martin Truffer, also at the University of Alaska Fairbanks (UAF), are presently answering these questions in one of the best ways possible: by flying over Alaska’s glaciers with a scanning laser and a radar to measure the size, shape, and thickness of Alaska’s glaciers. They fly their instruments approximately 1000 ft above the surface of representative glaciers every year or couple of years. The laser bounces light beams off the surface of a glacier that enables Chris and his team to measure the height and size of the glacier. Martin’s radar sends radio waves through the glacier that bounce off the bottom of the glacier and allows him to identify the glacier thicknesses. By making the laser measurements in the same place, year-after-year, Chris is able to tell how quickly these glaciers are changing their size. On average, Alaska’s glaciers are losing about 2 feet of ice thickness each year.
However, this decrease in glacier size is neither constant (i.e., the same from year to year) nor uniform (i.e., different glaciers are changing size at different rates). This multi-decade project, most recently funded by NASA’s Operation IceBridge mission, also allows Chris to learn more about the factors that make one glacier shed mass faster than another. When Martin’s radar results are included, they can make direct comparisons between the thickness of a glacier and changes in that same glacier thickness. Other interesting factors are glacier size, steepness, location, and whether a glacier ends in the ocean. All of these elements can effect changes in glacier size. And how these factors contribute or delay the wastage of Alaska’s glaciers is a topic that glaciologists are presently working hard to understand.
I recently joined Chris and Martin on their field work, along with glaciologist Evan Burgess, to survey some of the snowiest, most heavily glacierized locations in Alaska: the St. Elias Range, and the Stikine Icefield. A few of my pictures are below. I really enjoyed seeing so many different variations on the same theme. It was clear that many of the glaciers were getting smaller, but they are all get smaller in different ways: through thinning, slowing down the rate at which they flow, or becoming shorter.
I will continue my research on the behavior of ocean-terminating glaciers as a postdoctoral fellow in 2014.
I’m very excited to have accepted a postdoctoral fellowship at the University of Texas. I’ll be working with a great team to learn why three neighboring glaciers on the west coast of Greenland have behaved so differently over the last 10 or so years. I start with them this winter.