Tag Archives: Pictures

Heard Island’s Most Spectacular Outcrop

Head-on view of a block of Drygalski Formation (mixed volcanics and glacial sediments, here glacial sediments with volcanic clasts).  Image credit: Bill Mitchell (CC-BY).
Head-on view of a block of Drygalski Formation (mixed volcanics and glacial sediments, here glacial sediments with volcanic clasts). 53° 01.927′ S, 73° 23.704′ E. Image credit: Bill Mitchell (CC-BY).

Heard Island is home to a spectacular outcrop. It’s the coolest outcrop I’ve ever seen, besting the Bishop Tuff tablelands, the potholes along the St. Croix River at Taylor’s Falls, Zion Canyon, The Badlands, and various outcrops in Yellowstone and Grand Teton. Admittedly this outcrop doesn’t intrinsically have the scale of many of the others just mentioned—it’s a roughly car-sized block—but the power that went into creating it and the effect it created is truly amazing.

On its face (see above), it looks quite pedestrian: a block of lithified glacial till with clasts of vesicular basalt reaching up to grapefruit size. However, it’s important to consider it from a different perspective.

Side view of a block of Drygalski Formation.  From this view, it is much easier to see this is a ventifact (carved by the wind).  There is a pile of sand on leeward (left) side. Image credit: Bill Mitchell (CC-BY).
Side view of a block of Drygalski Formation. From this view, it is much easier to see this is a ventifact (carved by the wind). There is a pile of sand on leeward (left) side.
Image credit: Bill Mitchell (CC-BY).

When viewed from the side, a pile of sand in on the leeward (left, east) side of the block is evident. Additionally, the basaltic clasts of the rock face seem to be protecting the softer, tan-colored glacial matrix from the sand-blasting.

Here’s a close-up from an oblique angle:

Close-up, oblique view of the outcrop face.  Here the differential weathering (resistant grey clasts, weak tan matrix) is very apparent.  Spires of matrix are left to the leeward of the clasts, and are roughly horizontal. Image credit: Bill Mitchell (CC-BY).
Close-up, oblique view of the outcrop face. Here the differential weathering (resistant grey clasts, weak tan matrix) is very apparent. Spires of matrix are left to the leeward of the clasts, and are roughly horizontal.
Image credit: Bill Mitchell (CC-BY).

In the oblique view, the volcanic clasts making up the face of the outcrop are seen sheltering the matrix directly to the leeward from mechanical erosion. To tie all of these views together, I took a short video (embedded below).

This outcrop is located on the edge of a volcanic sand plain roughly 1.5×1.5 km. Strong westerly winds are present most of the time (9 m/s is average, measured at a site nearby).[1] In fact, the audio which accompanies the video is mostly wind noise, though there’s a little unintelligible chatter with my field partner, Carlos. Winds when the recording was made were “moderate” (for Heard Island) and from the west, exactly the kind of winds that shaped this outcrop. At the time of the recording, the winds weren’t strong enough to kick up much sand, nor were ice pellets falling from the sky, but on a gustier, stormier day, the face of this outcrop will take a beating.

Looking toward the ventifact outcrop from Windy City, Heard Island.  Although the outcrop itself is hidden behind the small reddish rise at center, this image illustrates the expanse of vegetation-free sand plain. Image credit: Bill Mitchell (CC-BY).
Looking toward the ventifact outcrop from Windy City, Heard Island. Although the outcrop itself is hidden behind the small reddish rise at center, this image illustrates the expanse of vegetation-free sand plain.
Image credit: Bill Mitchell (CC-BY).

In my travels and geo-adventures, I’ve seen differential weathering and ventifacts (outcrops shaped by wind), but never so strikingly combined as at this outcrop on Heard Island. That’s why I can confidently say it’s the coolest outcrop I’ve seen on Heard Island or anywhere else in the world.

[1] Thost, D., Allison, I. “The climate of Heard Island” in Heard Island: Southern Ocean Sentinel, ed by K. Green and E. Woehler. Surrey Beatty & Sons, Chipping Norton 2005, p. 52-68.

Windy City Gigapan

Processing the Windy City gigapan.  Image credit: Bill Mitchell (CC-BY).
Processing the Windy City gigapan. Image credit: Bill Mitchell (CC-BY).

This is the third in a series of three posts about the gigapan images taken on Heard Island (1: Big Ben, 2: Azorella Peninsula), with more information about the Windy City gigapan.

Windy City is located about 200 meters south of Atlas Cove, in the northwest portion of Heard Island. It comes from a fin of Drygalski Formation rocks, which are a mix of glacial sediments and volcanics, and is mostly surrounded by sand and gravel plains.

Looking closely at the outcrop, there are a number of interesting things to observe. First, there are the striking roughly-horizontal marks, which are particularly evident toward the base of the outcrop. Second, the outcrop is made of massive, fine-grained jointed rocks with few vesicles. Third, there are quite a few fractures within the rock, with discolorations along many of the cracks.

All of these observations combine into a remarkable tale of how Windy City has been formed. The massive, fine-grained, and jointed appearance leads to the conclusion that we are looking at a volcanic outcrop, rather than glacial sediments. Fracturing and discoloration have been brought on by weathering from the very wet, near-freezing environment. Finally, the wind has been a huge factor! Sand, gravel, snow, and graupel (ice pellets) have all been blasted against the side of this outcrop, primarily from the west (at right). On Heard Island, a 9 m/s wind is typical, with maximum recorded gusts exceeding 50 m/s on three days during the 1948-1954 period.[1] The high winds sandblast the outcrop, leading to the horizontal striations.

Here are a few wider-angle shots for context, and with better light than I ended up with for the gigapan.

Windy City outcrop, viewed from the north.  The gigapan image covers from my right arm to roughly the center of this image.  Image credit: Carlos Nascimento
Windy City outcrop, viewed from the north. The gigapan image covers from my right arm to roughly the center of this image. Image credit: Carlos Nascimento

Looking eastward at Windy City, with a person for scale.  The gigapanned portion of the outcrop is at right, but two spires of similarly eroded rock outcrop further to the north of the photographed portion.  The stake coming out from the outcrop is a marker for one of our temperature/light intensity sensors. Image credit: Carlos Nascimento
Looking eastward at Windy City, with a person for scale. The gigapanned portion of the outcrop is at right, but two spires of similarly eroded rock outcrop further to the north of the photographed portion. The stake coming out from the outcrop is a marker for one of our temperature/light intensity sensors.
Image credit: Carlos Nascimento

I also managed a close-up shot of one of the pieces of float.

Float rock at Windy City.  The 1:1000 metric scale at right is effectively a mm scale.  Some olive/green crystals are visible, mostly 1-5 mm in their longest dimension, which are likely olivine (possibly clinopyroxene). Image credit: Bill Mitchell (CC-BY).
Float rock at Windy City. The 1:1000 metric scale at right is effectively a mm scale. Some olive/green crystals are visible, mostly 1-5 mm in their longest dimension, which are likely olivine (possibly clinopyroxene).
Image credit: Bill Mitchell (CC-BY).

[1] Thost, D., Allison, I. “The climate of Heard Island” in Heard Island: Southern Ocean Sentinel, ed by K. Green and E. Woehler. Surrey Beatty & Sons, Chipping Norton 2005, p. 52-68.

When Counting Gets Difficult, Part 2

Prion sp., March 22, 2016, seen just west of Heard Island.  Image credit: Bill Mitchell.
Prion sp., March 22, 2016, seen just west of Heard Island. Image credit: Bill Mitchell.

Earlier I posed a question: suppose a group of 40 birds are identified to genus level (prion sp.). Four photographs of random birds are identified to species level, all of one species that was expected to be in the minority (fulmar prion) and likely would be present in mixed flocks. How many birds of the 40 should be upgraded from genus-level ID to species-level ID?

Clearly there is a minimum of one fulmar prion present, because it was identified in the photographs. With four photographs and 40 birds, the chance of randomly catching the same bird all four times is quite small, so the number of fulmar prions is probably much higher than 1. At the same time, it would not be reasonable from a sample of our photographs to say all 40 were fulmar prions.

If we have four photographs of fulmar prions (A), what is the minimum number of non-fulmar prions (B) needed in a 40-prion flock to have a 95% chance of photographing at least one non-fulmar prion?

To answer this question, I used a Monte Carlo simulation, which I wrote in R. I generated 40-element combinations of A and B ranging from all A to all B. Then for each of those populations, I ran 100,000 trials, sampling 4 random birds from each population (with replacement). By tracking the proportion of trials for each population that had at least one B, it becomes possible to find the 95% confidence limit.

pop_size <- 40  # Set the population size
sample_n <- 4  # Set the number of samples (photographs)
n_trials <- 100000  # Set the number of trials for each population

x <- seq(0:pop_size)  # Create a vector of the numbers from 0 to pop_size (i.e. how many B in population)

sample_from_pop <- function(population, sample_size, n_trials){
	# Run Monte Carlo sampling, taking sample_size samples (with replacement)
                # from population (vector of TRUE/FALSE), repeating n_trials times
	# population: vector of TRUE/FALSE representing e.g. species A (TRUE) and B (FALSE)
	# sample_size: the number of members of the population to inspect
	# n_trials: the number of times to repeat the sampling
	my_count <- 0
	for(k in 1:n_trials){  # Repeat sampling n_trials times
		my_results <- sample(population, sample_size, replace=TRUE)  # Get the samples
		if(FALSE %in% my_results){  # Look for whether it had species B
			my_count <- my_count + 1  # Add one to the count if it did
		}
	}
	return(my_count/n_trials)  # Return the proportion of trials detecting species B
}

create_pop <- function(n,N){  # Make the populations
	return(append(rep(TRUE,N-n),rep(FALSE,n)))  # Populations have N-n repetitions of TRUE (sp. A), n reps of FALSE (sp. B)
}

mypops <- lapply(0:pop_size, create_pop, pop_size)  # Create populations for sampling

# Apply the sampling function to the populations, recording the proportion of trials sampling at least one of species B
my_percentages <- sapply(mypops, sample_from_pop, sample_size=sample_n, n_trials=n_trials)

My simulation results showed that with 22 or more birds of species B (non-fulmar prions), there was a >95% that they would be detected. In other words, from my photographic data, there is a 95% probability that the flock of 40 prions contained no fewer than 19 fulmar prions.

Let’s take a look at it graphically.

library(ggplot2)

mydata <- data.frame(my_percentages, 0:pop_size)  # Make a data.frame with the results and the # of species B
names(mydata) <- c("DetProb", "B")  # Rename the columns to something friendly and vaguely descriptive

p <- ggplot(mydata2, aes(x=B,y=DetProb)) + geom_point() # Create the basic ggplot2 scatterplot
p <- p + geom_hline(yintercept=0.95)  # Add a horizontal line at 95%
p <- p + theme_bw() + labs(x="# of species B (pop. 40)", y="Detection probability of B")  # Tidy up the presentation and labeling
print(p)  # Display it!
Results of the Monte Carlo simulation.  At left is all A, while at right is a population with all B.  The horizontal line is the 95% probability line.  Points above the line have a >95% chance of detecting species B.
Results of the Monte Carlo simulation. At left is all A, while at right is a population with all B. The horizontal line is the 95% probability line. Points above the line have a >95% chance of detecting species B.

With 22 or more non-fulmar prions, there’s a >95% chance one would be photographed. With 19 fulmar prions and 21 non-fulmar prions, there’s a >5% chance the non-fulmar prions would be missed. So our minimum number of fulmar prions is 19. I may have seen a flock of 40 fulmar prions, but there aren’t enough observations to say with statistical confidence that they were all fulmar prions.

When Counting is Difficult

A fulmar prion glides swiftly over the swell of the Southern Ocean.  Image credit: Bill Mitchell (CC-BY)
A fulmar prion glides swiftly over the swell of the Southern Ocean. Image credit: Bill Mitchell (CC-BY)

During the Heard Island Expedition, including the nearly three weeks at sea on the Southern Ocean, I made a few observations for a citizen science project: eBird. It’s a pretty simple system: identify and count all the birds you see in a small area and/or time period, then submit your list to a centralized database. That database is used for research, and keeps track of your life/year/county lists. With so few observations in the southern Indian Ocean in March and April (and no penguins on my life list before the expedition), I figured I would make a few counts.

On its face, identifying and counting birds is straightforward. Get a good look, maybe a photograph, and count (or estimate) the number present of that species.

It gets more difficult when you go outside your usual spot, particularly when the biome is much different. Although I have some familiarity with the Sibley Guide for North American birds, I’ve never payed very close attention to the seabird section, and have never birded at sea before. All the birds I expected to see on this expedition would be life birds, and that changes things a bit. I would have to observe very closely, and photograph where I could.

Before the expedition, I read up on the birds I would likely find on the island. In addition to four species of penguins, there were three species of albatross (wandering, black-browed, and light-mantled sooty) and two species of prions (Antarctic and fulmar). Albatrosses are large and the species near Heard are readily distinguished. Prions, however, can be quite difficult even with good observations. They’re not quite to the level of the Empidonax flycatchers, but close.

At sea, we usually had prions flying near the ship. I took pictures, knowing that I might be able to get help with ID if I needed it—and of course I needed it.

That’s where the problem started: I had a count where I had observed 40 prions flying around the ship, which I identified only to genus level. From my reading on Heard Island, I knew that breeding populations for prions on Heard Island were generally larger Antarctic prions than fulmar prions, with an estimate of a 10:1 margin. I had four clear pictures of individual birds, which my helpful eBird reviewer was able to get to an expert for further identification. All four were fulmar prions.

With 40 birds identified to genus level, and four photos of random birds identified to species level as a species expected to be a minor proportion, how many of the original 40 birds can I reasonably assign as fulmar prions?

I have an answer to this question, which I will post next week.

Azorella Peninsula Gigapan

Processing the Azorella Peninsula gigapan.  Image credit: Bill Mitchell (CC-BY).
Processing the Azorella Peninsula gigapan. Image credit: Bill Mitchell (CC-BY).

This is the second in a series of three posts about the gigapan images taken on Heard Island (1: Big Ben, 3: Windy City), with more information about the Azorella Peninsula gigapan.

The Azorella Peninsula is on the northern edge of the main part of Heard Island, east of the Laurens Peninsula. It forms the eastern boundary of Atlas Cove (Laurens Peninsula forms the western boundary; see map below). At the west end of the Azorella Peninsula’s southern margin is the heritage zone around the ANARE campsite, two water-tank shelters, a green “apple” shelter, and the area where our expedition made camp. That many of the camps are all in the same area is no accident: Atlas Cove is probably the best harbor on the island (though still not sheltered from a northerly swell), there is a convenient beach for boat landings, and a small step up of elevation from the lava flows of the Azorella Peninsula provides higher ground than the sometimes-inundated Nullarbor.

Heard Island Map, 1985. Image credit: excerpt from the Division of National Mapping.
Heard Island Map, 1985. Image credit: excerpt from the Division of National Mapping.

Getting a gigapan here was not as straightforward as I had hoped. Although there were plenty of pahoehoe flow tops, cracks where a flow had deflated and collapsed in on itself, and other lava flow features, few of them were of a scale and in a location which enabled them to be nicely gigapanned with the tripod I had. With another 3–5 m of elevation, the gigapan would be spectacular.

As it was, there were some additional features besides the lava flows which I wanted to include. For one, the landscape has significant erosional processes happening, and there are sandy areas which get washed when it rains. Even more than the rain, though, the wind creates eolian features. Many of the small rocks have a little dune in their lee, and often the Kerguelen cabbage and Azorella moss grow on the leeward side of rock barriers as well. Some of this organization is visible in the gigapan.

At the top right of the Gigapan image, and lost to the fog and overexposure of the image, is a strongly layered prominence: Corinth Head. Although I would have liked to go see this outcrop up close, our permit did not allow that—the area is a major nesting site for burrowing seabirds, and in places there are lava tubes with thin ceilings which may give way underfoot.

Corinth Head, Heard Island, viewed from the south (further east than the Gigapan was taken).  Layering is clearly visible, and is likely of igneous origin.  Image credit: Bill Mitchell (CC-BY).
Corinth Head, Heard Island, viewed from the south (further east than the Gigapan was taken). Layering is clearly visible, and is likely of igneous origin. Image credit: Bill Mitchell (CC-BY).

Where the Azorella Peninsula lava flow field meets the Nullarbor, there was a little flow which caught my eye. There, one flow clearly traveled through an older channel or tube. Weathering has removed some of the older flow, giving a cross-sectional view of the dark vesicular rock.

Lava flows of the Azorella Peninsula meet the Nullarbor.  An older, grey unit is visible with a redder unit in the middle.  Notebook is 19 cm wide.  Image credit: Bill Mitchell (CC-BY).
Lava flows of the Azorella Peninsula meet the Nullarbor. An older, grey unit is visible with a redder unit in the middle. Notebook is 19 cm wide. Image credit: Bill Mitchell (CC-BY).

Some lava tubes showed obvious signs of deflation or lava tube collapse. The one seen below had eolian features nearby, and the Kerguelen cabbage and Azorella moss can be seen growing on the leeward side of the rocks. An elephant seal is also present.

Deflated lava flow beside the Nullarbor on the Azorella Peninsula, Heard Island.  Some eolian features are present.  Note the Azorella moss and Kerguelen cabbage at right, in the lee of the solid rocks.  The tan mass at right is an elephant seal.  Notebook is 12x19 cm.  Image credit: Bill Mitchell (CC-BY).
Deflated lava flow beside the Nullarbor on the Azorella Peninsula, Heard Island. Some eolian features are present. Note the Azorella moss and Kerguelen cabbage at right, in the lee of the solid rocks. The tan mass at right is an elephant seal. Notebook is 12×19 cm. Image credit: Bill Mitchell (CC-BY).

Finally, here is another example of a collapsed lava tube, which shows off a cross-section of the top of the lava tube as well as some pahoehoe flow tops.

A collapsed lava tube on the Azorella Peninsula, Heard Island, gives a cross-sectional view of the roof of the lava tube.  Kerguelen cabbage plants in foreground are roughly 25 cm across.  Several pahoehoe flow tops are visible: small-scale in the foreground, and large-scale in the center toward the top of the image.  Image credit: Bill Mitchell (CC-BY).
A collapsed lava tube on the Azorella Peninsula, Heard Island, gives a cross-sectional view of the roof of the lava tube. Kerguelen cabbage plants in foreground are roughly 25 cm across. Several pahoehoe flow tops are visible: small-scale in the foreground, and large-scale in the center toward the top of the image. Image credit: Bill Mitchell (CC-BY).

Pictures from the Field

Standing just outside the tents at Atlas Cove, Heard Island, on a clear evening.  Note that there is no incandescence from lava on Mawson Peak.  Image credit: Adam Brown.
Standing just outside the tents at Atlas Cove, Heard Island, on a clear evening. Note that there is no incandescence from lava on Mawson Peak. Image credit: Adam Brown.

A few days have gone by, and they have been busy! We’ve been fortunate in that when the weather has been poor, the radio propagation has been good. A fair bit of windy, drizzly weather has been present this week, and we have managed to make more than 50,000 contacts with stations all around the world.

Unfortunately, the weather has meant I haven’t had the opportunity to take more gigapans. I am prepared for wet weather, and this morning I went a few hundred meters across the lake which had formed in front of camp (ankle deep) to Wharf Point, the point inside Atlas Cove. There on the cobbles lining the beach I did a stationary count of the birds in the hummocks nearby, on the water, and along the beach. It took about 10 minutes, and I managed to get the list recorded in a weatherproof notebook for upload later. Getting out of the tent and away from things for a while was a welcome change.

Inside the operating tent are many tables with radio equipment.  We have six stations set up, two of which are outside the frame to the left.  The galley is just barely showing on the right, and I'm standing in the front door.  The sleeping tent is through a little hallway.  From left to right, by leftmost extent of the head, we have Adam, Dave Lloyd, Jim, Vadym, Ken, Arliss, and Hans-Peter.  Image credit: Bill Mitchell (CC-BY)
Inside the operating tent are many tables with radio equipment. We have six stations set up, two of which are outside the frame to the left. The galley is just barely showing on the right, and I’m standing in the front door. The sleeping tent is through a little hallway. From left to right, by leftmost extent of the head, we have Adam, Dave Lloyd, Jim, Vadym, Ken, Arliss, and Hans-Peter. Image credit: Bill Mitchell (CC-BY).
The sleeping tent, which sleeps 14.  Although there are windows, they are kept shuttered all day.  It's a good place to sleep, but not particularly warm.  Image credit: Bill Mitchell (CC-BY).
The sleeping tent, which sleeps 14. Although there are windows, they are kept shuttered all day. It’s a good place to sleep, but not particularly warm. Image credit: Bill Mitchell (CC-BY).

One thing which has been abundantly clear on this expedition is that if you want to do something that depends on the weather, be prepared to do it. The weather can shift very rapidly (especially if it’s permissive weather), so “I’ll just wait until later” often won’t cut it. If you see Big Ben and want a photograph of it, get your camera and shoot. There may not be another chance. This evening I didn’t immediately take a picture when there was a clear, starry sky. I at least saw the starry sky, but did not get the photograph. With only a bit more than a week to go, I hope I can still get that picture.

In the afternoon a few days ago, the weather cleared enough to get a view of Mawson Peak atop Big Ben. I quickly grabbed the camera, put on the telephoto lens, and got a few pictures of the summit. Indeed, there was a small plume indicating (at minimum) hydrothermal activity or venting, but possibly a small active lava flow.

Mawson Peak with a small plume indicating volcanic activity.  Image credit: Bill Mitchell (CC-BY).
Mawson Peak with a small plume indicating volcanic activity. Image credit: Bill Mitchell (CC-BY).

Heard Island’s mood changes with the weather, and the effect that has on the landscape can be quite striking. The picture at the top of this post and the one immediately below are taken in pretty similar places looking in similar directions. What a difference the weather makes!

Antenna Lake, Atlas Cove, Heard Island.  Rain fell fast enough to flood much of the low-lying volcanic sand plain near our camp.  We were glad not to have camped there, and the antennas still worked.  It looks quite other-worldly, with the dark, broken lava flows and fog concealing the mountain.  Image credit: Bill Mitchell (CC-BY).
Antenna Lake, Atlas Cove, Heard Island. Rain fell fast enough to flood much of the low-lying volcanic sand plain near our camp. We were glad not to have camped there, and the antennas still worked. It looks quite other-worldly, with the dark, broken lava flows and fog concealing the mountain. Image credit: Bill Mitchell (CC-BY).
Camp seen on a rainy, dreary day typical of Heard Island.  Image credit: Bill Mitchell (CC-BY).
Camp seen on a rainy, dreary day typical of Heard Island. Image credit: Bill Mitchell (CC-BY).

Finally, the king penguins make tracks as they walk around on the wet sandy ground.

King penguin tracks in the sand of the nullarbor, Heard Island.  Each track is roughly 8 cm in length.  Image credit: Bill Mitchell (CC-BY).
King penguin tracks in the sand of the nullarbor, Heard Island. Each track is roughly 8 cm in length. Image credit: Bill Mitchell (CC-BY).