Summer Research at Wooster: Rain-on-Snow in Alaska

July 13th, 2018

The following post is courtesy of Anna Cooke (’20), who worked with Dr. Alex Crawford through Wooster’s Sophomore Research Program this summer

In the heat of Ohio’s summer, it’s been a small bit of relief to turn my attention to Alaska; or more specifically, to rain on snow events in Alaska. A rain on snow event is pretty much exactly what it sounds like. It occurs when rain falls on a preexisting snowpack. For this to happen, the temperature must rise above freezing during a precipitation event. If the temperature then falls below freezing following the event, the result is a layer of ice on the surface of, in, or underneath the snowpack.

But why should those of us who live in the continental interior care?

Rain on snow, hereby referred to as ROS, has some interesting and possibly devastating effects. One such effect is on caribou populations. The diet of Alaskan caribou varies, but something that most caribou have in common is the dependence on ground foliage, such as lichens, as a winter food source (Joly et al., 2015). ROS is dangerous for caribou because of the possibility that the resulting ice layers will block this food source. Nutritional stress caused by ROS can lead to declining birth rates and calf weights. At the most extreme, mass die-offs can result from starvation (Mallory and Boyce, 2018). The resulting population decline or emigration of caribou impacts the hunters who rely on the caribou as a food source.

Fig 1: Caribou photo courtesy of Dr. Karen Alley.

Other impacts of ROS include the shutdown of airports and loss of revenue from tourism, and permafrost degradation. If enough rain infiltrates through the snowpack to its base, when it refreezes, the latent heat that is released will maintain a soil temperature of 0 degrees Celsius when it should be much colder. The resulting warming of subsurface temperatures could destabilize permafrost systems, causing slope instability and avalanches (Rennert et al., 2009).

Identifying ROS Events

If we want to mitigate the effects of ROS events, it is important that we understand where, when, and how often they occur. To do this, ROS can be identified and analyzed using climate models, satellite data, and observational data from weather stations. One difficulty in identifying ROS events is that no one agrees on just what a ROS event is. Some people define it as 3 mm of rain falling on 5 mm of snow water equivalent, or SWE, which is the amount of water present if the snowpack were to be melted. Others use different thresholds than 3 and 5 mm. Some use measures such as over 12 continuous hours of precipitation visually classified as drizzle and greater than 0.0 mm.

Despite this variation all identification strategies share one limitation: none keep track of refreezing after the precipitation event. This is an issue because ROS without refreezing does not have the same impacts as ROS followed by freezing, and if we are interested in the events most likely to have strong effects, refreezing is imperative.

I experimented with different identification strategies and thresholds trying to find a method that was restrictive enough that I wasn’t overcounting the number of events, but not so stringent that I was undercounting. The graphs below show the average number of events per year divided by season at five different weather stations in Alaska when counting events as 0.1 inches of precipitation on 0.1 inches of SWE, or 1 inch of snow depth for stations where SWE is not available. The first graph shows the total number of ROS events counted. The second graph shows the number of ROS events followed by refreezing. In all cases, fewer events are counted when refreezing is accounted for, and in several cases no more than half of ROS events are followed by refreezing. Thus, it’s likely that many studies are overestimating the number of impactful ROS events.


Fig 2: Number of rain on snow (ROS) events per year by season for (top) all events and (bottom) events followed by refreezing.

As you can see from the graph above, most ROS events seem to occur in the spring, which is defined as March, April, and May. ROS functions a bit differently depending on the season. In the fall, the temperatures are often warm enough for rain to occur, but there may not be a snowpack for the rain to fall on. In the winter, the limiting factor is not snowpack, but rain, since the precipitation that falls is more likely to be snow. In the spring, the presence of a snowpack and the increase of the temperature to allow for rain are likely. However, a refreezing event is less likely. Moreover, even if there is refreezing afterwards, the number of days that the temperature remains below freezing is likely to be lower than the number of days for a winter event.

As such, events in each season pose different threats to caribou herds. In the fall, healthy caribou which have spent the summer with plentiful food access are more likely to be weakened than killed off. However, major winter events in which the snowpack is frozen over for weeks afterwards are more likely to decimate populations. Events in the spring are also dangerous because, even though the ice is not likely to inhibit foliage access for more than one or two weeks at a time, caribou may already be weakened from harsh winters.

Since there are so many factors to take into account in the study of ROS events, more research is necessary, especially since the frequency with which events occur is likely to increase with global warming. There are ways that we can mitigate the effects of ROS on wildlife and human populations, but only if we can understand its causes and effects. The research done this summer is piece of a larger story, and it was a pleasure to add this piece to the puzzle.

Fig 3: Caribou photo courtesy of Dr. Karen Alley

Works Cited:

  • Joly, Kyle, Samuel K. Wasser, and Rebecca Booth. 2015. Non-Invasive Assessment of the Interrelationships of Diet, Pregnancy Rate, Group Composition, and Physiological and Nutritional Stress of Barren-Ground Caribou in Late Winter. PLoS One, 10 (6): 1-13 (DOI: 10.1371/journal.pone.0127586).
  • Mallory, Conor D. and Mark S. Boyce. 2018. Observed and predicted effects of climate change on Arctic caribou and reindeer. Environmental Reviews, 26 (1): 13-25.
  • Putkonen, J., T.C. Grenfell, K. Rennert, C. Bitz, P. Jacobson, and D. Russell. 2009. Rain on Snow: Little Understood Killer in the North.EOS,90 (26): 221-222.
  • Rennert, Kevin J., Gerard Roe, Jaako Putkonen, and Cecilia M. Bitz, 2009. Soil Thermal and Ecological Impacts of Rain on Snow Events in the Circumpolar Arctic. Journal of Climate,22: 2302- 2314 (DOI: 10.1175/2008JCLI2117.1).

Wooster Geologist in Wales and England (June 2018)

June 20th, 2018

I spent two weeks in wonderful places making presentations, doing research, scouting for student Independent Study projects, and seeing friends and colleagues. Here is a guide to the blog posts by date —

June 6: Bryozoologists gather in Wales
June 7: Bryozoologists on the rocks in South Wales
June 8: Last day of the Larwood meeting: Museum collections and a coal mine tour
June 9: A Smith Map in Wales
June 10: A Wooster Geologist in Wales (continued)
June 11: A narrow-gauge train trip in Mid Wales
June 12: Bored marbles, slate mines, and a castle in North Wales
June 13: Last day for this Wooster Geologist in Wales … for now
June 14: Stone cannon balls from Aberystwyth Castle
June 15: Wooster Paleontologist in London (again)

Thank you to Caroline Buttler, Tim and Caroline Palmer, and Paul Taylor for being such excellent, generous and creative hosts!

Wooster Paleontologist in London (again)

June 15th, 2018

London, England — The Natural History Museum is one of my favorite places on Earth. It is a secular cathedral of science; a celebration of life’s long history and glorious diversity. I’ve had the pleasure of working here many times, and each visit renews the enchantment. I’ve arrived to do a few days work in Paul Taylor‘s lab and the associated fossil collections.

Inside the bowels of the museum are thousands of drawers of specimens carefully preserved for research. This is an example of one drawer. It happens to be full of Ordovician bryozoans.

It may look chaotic, but this is a center of fossil bryozoan research — Paul Taylor’s office and lab. I’ve been visiting Paul in this space since 1985. Note the small patch of labelled specimens on the desk in the foreground. They’re from me.

These are specimens I brought for us to study. The brown one on the left is a bryozoan-encrusted bivalve collected this year in the Middle Jurassic of Utah. The pink-labelled specimens come from Macy Conrad’s (’18) Independent Study work, part of our team project on Upper Cretaceous bryozoans from SW France. Eventually many of these fossils will be imaged with the NHM Scanning Electron Microscope, with which Paul is a master.

This year I’m staying in a small hotel near the Earl’s Court tube station, just a 15-minute walk from the museum. Very convenient.

With this post my Wales and England travel posts end. Later I’ll write about the results of our various projects. Thank you again to my hosts Caroline Buttler, Tim & Caroline Palmer, and Paul Taylor. I am fortunate to have such friends and colleagues.

Stone cannon balls from Aberystwyth Castle

June 14th, 2018

Today I made the long train journey from Aberystwyth to London, so I have just a brief post about the spherical stone objects above. They are stone cannon balls recovered in an archaeological investigation of Aberystwyth Castle. Tim Palmer is examining them to determine from what geological units they derive. They were hand-carved to fit into the Medieval cannons used during a siege of the castle.

Caroline Palmer wrote an excellent description and interpretation of these cannon balls in her great blog Letter from Aberystwyth. She wrote of two of them: “One is of limestone from Dundry near Bristol, and the other of a dense greeny-grey sandstone which could be from Somerset or South Wales. The surface is crudely tooled and pitted and to the casual glance they look strangely like a pair of seriously decayed Galia melons. They are heavy, 5½lb and 6½lb respectively, and just under 6 inches diameter. One has scarring on its side which could have been a result of its violent impact on the castle.” Check out her post for images of Medieval cannons and accounts of how they worked.

This is the cannon ball likely made of Dundry Stone. I suspect Dundry Stone, a Middle Jurassic Limestone, is Tim’s favorite building stone. Now we need a study to see how it can withstand whacking against a castle wall!


Last day for this Wooster Geologist in Wales … for now

June 13th, 2018

Aberystwyth, Wales — My last full day in Wales with my hosts Tim and Caroline Palmer was again different from every other day in this country. I have had a stimulating diversity of experiences on this short trip. For example, today we visited the Iron Age village reconstruction of Castell Henllys in Pembrokeshire (above), which was very new to me. The roundhouses are constructed on the actual archaeological site, with even the posts placed in the ancient postholes.

Some roundhouses are left unfinished to show the post and wattle construction, the walls of which would be later daubed with mud and the characteristic round thatched roof attached.

This is one of the reconstructed rooms, complete with Celtic gear circa 2300 years ago. The village is maintained as a living museum, so fires are kept smoldering for an appropriately smoky interior.

We also spent time in St. David’s Cathedral in Pembrokeshire. Tim gave me a stone-and-history tour inside. A fee was required to take photographs, so I abstain. You’ll just have to imagine Medieval stone effigies, towering pillars, and centuries of stone memorials.

Our last stop was the small and unique St. Lawrence’s Church in Gumfreston. This church was built in the 12th century, likely on a site that had an earlier structure.

Tim, of course, set to work identifying the building stones, using a torch and handlens. He is here examining some sort of stone basin fixed between the porch and church wall. It may have held holy water.

Very near the church is a set of three springs, conveniently labelled “holy wells”. The sacred attribution to these springs goes back much earlier than the church, probably to Celtic times. The church, in fact, holds periodic Celtic Christian “services of light”, and an oak tree overhanging the springs is decorated with ribbons.

A geological question is why the water in these springs has bubbles of gas emanating from below? Is this methane from vegetation? Carbon dioxide? Is it related to a local fault system? There is actually a webpage for the Gumfreston holy wells. It says the waters are rich in carbonic acid, so carbon dioxide the bubbles may be. The site also says, “According to tradition, the uppermost spring is pure water, middle one chalybeate and lower one sulphur although all appear to be chalybeate.” Chalybeate is a new word for me. It means the water contains “salts of iron”. The website also has this classic bit of sympathetic magic: “Traditionally cures such as leg problems were associated with the upper spring due to its shape like a leg, the middle for hands and arms, and the lower for eyes.”

Otto is the Palmer’s delightful Lhasa Apso and our companion on most of our Welsh adventures. This picture was taken just before he jumped into the lower well. We can assume, then, that his eyes are now blessed.

Thank you again to Tim and Caroline Palmer, and Caroline Buttler, for making my time in Wales so enriching, educational, and fun. Just let me know when you want to see the magical sites in Ohio!

Bored marbles, slate mines, and a castle in North Wales

June 12th, 2018

Aberystwyth, Wales — Let’s start with the castle as my tour of Wales with Tim and Caroline Palmer continues. Above is the storied Harlech Castle in North Wales. It was built of sandstone blocks by Edward I in the 13th century, passing through four major conflicts: The Revolt of Madog ap Llywelyn (1294–95), the Revolt of Owain Glyndŵr (1400–09), the Wars of the Roses (1460–68), and the English Civil War (1642–47). The siege in 1468 apparently inspired the stirring song “Men of Harlech“. (Hear it and read the lyrics on this YouTube page. The song is unforgettable in the 1964 film Zulu.)

When built, Edward I made very sure Harlech Castle could be supplied by sea, so there was a water-gate on the shore. This is now the view of the ocean from the castle — it is far away, with a significant dune field along the shore. I could not find out why the shoreline retreated from the castle; it may have been a combination of sedimentation and isostatic rebound of the land in slow response to the end of glaciation.

In 1709 a ship sank off the coast of Barmouth, Wales, submerging an expensive load of 43 blocks of Carrara Marble from Italy. One two-ton block was recovered after centuries on the seafloor and sculpted by an artist (Frank Cocksey) to celebrate the millennium. It is called The Last Haul, representing three generations of fishermen pulling in a net.

It is beautiful carving … but you know I’m not showing it for the art. Check out the holes throughout!

This marble block is heavily bioeroded by marine organisms, producing the clavate borings Gastrochaenolites (by bivalves), a network of connected small chambers (Entobia, made by sponges), and long narrow cylindrical borings known as Trypanites (by worms). There is a cool story to sort out here about the pattern and rate of bioerosion in these cold seas. [UPDATE: The Curious Scribbler has a new post on these marbles with lots of information and ideas. You may even recognize some people in the images.]

Our last site of the day was the Welsh town of Blaenau Ffestiniog. Slate mining made this place, starting in the middle of the 18th century. The surrounding mountains have a rich grade of Welsh slate useful for many industrial and structural applications. The town square (above) has a monument to its slate heritage.

This mountain above Blaenau Ffestiniog has been heavily carved for its slate.

One quarry remains operational. The Welsh slate industry declined significantly during World War I and never fully recovered. Note the massive mounds of slate debris.

Slate mining produces large amounts of waste rock. Up to 90% of the slate removed from a quarry is unusable and piled up. Blaenau Ffestiniog is surrounded by man-made mountains of loose slate debris.

Thus ended another diverse day of Welsh experiences with Tim and Caroline Palmer.

A narrow-gauge train trip in Mid Wales

June 11th, 2018

Aberystwyth, Wales — Caroline Palmer provided Tim and me a wonderful experience in a scenic Welsh valley on a perfect Welsh day. She is Trustee of the nearby Hafod Estate ( … one of the finest examples in Europe of a Picturesque landscape.”) This estate is one of the places where pine martens have been re-introduced to Wales from Scotland. In that office she received three tickets (and lunches) for us to take a ride on one of the “Great Little Trains of Wales” to a celebration of a new train carriage and a Pine Marten center. It was delightful for both the natural views and the people involved.

We took the Vale of Rheidol Railway with this coal-fired steam engine pulling our narrow-gauge carriages. We sat in the open car directly behind the engine, so I could watch the crew in action and feel the occasional cool droplets condensed from the steam (and a whiff or two of coal smoke).

This was our route from Aberystwyth to Devil’s Bridge. (Map from Wikipedia.)

A view from the train traveling up the Vale of Rheidol. Very green and steep.

This valley has numerous silver and lead mines from the early 20th century and before, leaving scattered tailings piles like this one, along with significant heavy-metals pollution in some places.

We were greeted in Devil’s Bridge by the Mynach Community School Choir singing Welsh songs. They were fun. I felt the red-headed boy’s discomfort, though!

We ended the delightful day with a quick visit to the 13th century Aberystwyth Castle, a remnant of which was brilliantly lit by the setting sun.

A Wooster Geologist in Wales (continued)

June 10th, 2018

Aberystwyth, Wales — After the successful Larwood Meeting in Cardiff, I took a train to Carmarthen and met my friends Tim and Caroline Palmer for a delightful few days in Wales seeing building stones and geological sites. I’ve known Tim and Caroline since 1985, and Tim and I have published much together. Not only was I again adding to my knowledge of geology (and as always thinking of student Independent Study projects), but I was seeing old friends with whom I have much in common.

Above is Laugharne Castle in the town of Laugharne of Dylan Thomas fame. The castle was originally built by the Norman lords as part of a chain of strongholds to constrain the Welsh. You can read about the history of the site here.

The rock on which the castle was built was even more interesting, of course. It is Old Red Sandstone (Devonian), showing a facies a bit mysterious to us. It has trace fossils (Diplocraterion?), climbing ripples, and what may be dewatering structures.

One of my favorite activities is to go into Medieval churches with Tim and study the building stones and other stonework. Here is Tim examining an effigy in the Llanfihangel Abercywyn church interior. Tim is an expert on building stones in Great Britain, especially the sedimentary ones used most often in Medieval and earlier structures.

The baptismal font is usually the oldest stone object in a church because it can survive longer than larger, more complex parts.

A very special treat was seeing this stone at the end of our day. It is a monolith 1.4 meters high inscribed with “CORBALENGI IACIT ORDOVS”. This translates to: “Here lies Corbalengi the Ordovician”. It is thus called the Corbalengi Stone. It is Celtic and probably from the sixth century. It is one of the very few inscriptions mentioning the Ordovices tribe, from whom the geological period Ordovician is named. For those of us who work in the Ordovician, this is special. We like to think of Corbalengi as the Last of the Ordovices, although there is no other evidence for this.

A closer view of the Corbalengi Stone.

A much better image of the Corbalengi Stone, taken from this site. What a great start for the second half of my explorations of Wales.

Finally, I had to add this image of driving in Wales. This is a two-way road. Tim is a superb driver, for which I’m grateful!


A Smith Map in Wales

June 9th, 2018

Cardiff, Wales — Today Caroline Buttler and I met in the National Museum Wales and worked on an Ordovician bryozoan project together. There was nothing very picturesque going on until Caroline asked if I wanted to see their original William Smith 1815 geological map of England and Wales. The map that changed the world? Of course! There is part of it carefully unfolded above.

I professionally intersected with The Map on its 200th anniversary in 2015. I participated in a celebratory symposium at the annual Geological Society of America meeting, giving a talk entitled: “William Smith as a paleontologist: his views on the origin of fossils, their preservation and the history of life.” (Geological Society of America Abstracts with Programs 47(7): 24.) It was fun and I’ve closely followed studies of Smith and his map since then. This was thus a treat! Thanks, Caroline.

Last day of the Larwood meeting: Museum collections and a coal mine tour

June 8th, 2018

Cardiff, Wales — On our last day of the Larwood Meeting, we finished up business in the morning and then had guided tours of the marine, mollusc, and fossil collections in the National Museum Wales (above).

Highlights for me included this modern gastropod shell (a cold-water whelk from Alaska) collected by my hero Captain James Cook in 1778 a year before he was killed. A quote from Cook: “Ambition leads me … farther than any other man has been before me”. James Kirk of Star Trek is partly modeled after him.

Here’s another evocative modern shell: Conus gloriamaris, once thought to be the rarest shell and thus enormously valuable.

Here is the label for the specimen. It lists the 12 known specimens at the time. It is still popular among collectors, but now much more common. The excellent mollusc type collection of the Cardiff Museum is online.

The last activity for the Larwood crew was a tour of a coal mine turned into a museum: The Big Pit. Coal in South Wales played a huge role in the Industrial Revolution, as did Welsh iron ore. This mine tells the story of coal in Wales by taking visitors underground into the workings.

We couldn’t take images in the mine itself because of fire hazards, but Hans Arne Nakrem got a shot of the group prepared to go down the shaft. We had a great time with our story-telling guide. Our walk through the tunnels was punctuated by the loud bangs of my helmet on the ceilings. (It’s not just that I’m tall — it’s also that I bend far less!)

And that was the end of the 15th Larwood Meeting. Thank you again to Caroline Buttler and her team for such an excellent event. We all learned more about our precious bryozoans, with the bonus of getting to explore parts of beautiful South Wales.

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