Geoscientist’s Toolkit: Topographic Maps

Topographic map, excerpt from the USGS 7.5' Series (Winona West Quadrangle)
Topographic map, excerpt from the USGS 7.5′ Series (Winona West Quadrangle (31 MB PDF))

Topographic maps (sometimes just “topo maps”) can tell a lot about a place. They record the varying heights of land, from which inferences can be made about those places and their geology. For instance, despite the claims many people make about Minnesota being a flat place, the map above shows something quite different. Sure, there are no 4 km tall peaks here, but this map contains a 500′ embankment, and many stream channels cutting 300′ down from the hilltops.

With the right perspective, understanding a topographic map is fairly straightforward. Let me tell you a story about topo maps.

When I was in eighth grade, my science teacher, Ms. Fuller, was teaching us about maps and mapping. Rather than just looking at maps, we were going to make maps. On a cool, cloudy fall day, we all loaded onto a school bus for a field trip to a nearby park with a lake in it. The students had been divided into teams of three, and each was given a pair of metersticks and a long tape measure.

As we walked along the path at the water’s edge, every so often (50-100′) a team would be assigned to measure a profile up the hill. One person, Alice, would hold a meterstick upright at the path, and another, Bob, would walk directly away from the lake until his feet were level with the top of Alice’s meterstick. Here, Bob would hold his meterstick upright. The third team member, Eve, then measured and recorded the distance between the two metersticks, from the top of Alice’s to the base of Bob’s. Once that had been done, Alice would make her way through the brush, past Bob, and up the hill until her feet were level with the top of his meterstick. The distance between them was measured, and the process repeated until they had gone ~75 m away from the lake and reached the top of the hill and the edge of the park. If they had extra time, they measured another profile from a different location around the lake.

Back in the classroom, Ms. Fuller compiled the profile data into a topographic map, and added in bathymetric (depth beneath the lake surface) data from an outside source (pardon the pun). You may think that just took the interesting part out of the exercise, but let me assure you, it did not!

The following day in class, we were given a large (18″x18″?) printed copy of the topographic map. On it was a North arrow, and a bold line indicating the edge of the lake. Now the challenge was to build a model of the lake and its surroundings.

We spent the day cutting out pieces of cardboard to match the contour lines. Or rather, we cut the insides out of 18″x18″ cardboard pieces, since the lake area was generally bowl-shaped. Each layer represented a certain amount of height, probably around 3 m. In another class period or two, we had our cardboard pieces fully cut out and glued together, giving us a 3D model of the area. All that was left was to make it look nice. The water was painted one color (typically blue or white, depending on whether we were feeling wintry), and the land a different color (usually green). North arrows were added (for full points), as were horizontal and vertical scale bars (the two scales being different).

Contours on topographic maps represent places where the surface of the Earth passes through a geometric plane for a certain elevation. It’s a slice. Give the slice a width, such as the thickness of corrugated cardboard, and by putting contours together you can arrive at a model of the area.

Places where contour lines are close together are very steep: there is a great change in elevation in a short distance. Areas with few contour lines and large spacing between them are quite flat.

If you have a moment, find your local topographic map, and see what it looks like (US topo maps can be downloaded from the USGS). Alternately, you can enable the terrain overlay on Google Maps (in map mode, not satellite), but you don’t get the excitement of the quadrangle names, the 1:24,000 scale, and the magnetic north arrow.

Introduction to the Geologic Timescale and Geochronology

Geologic Time Scale. Image credit: GSA.

The Earth is pretty old.[1] Before we start talking about rocks, it is important to understand how to talk about time from scales of a human lifetime (50-100 years) to the age of the planet (~4.6 billion years). This is geochronology [Etymology: geo: Earth; chrono: time; logy: study].

Earth time is measured in units of a year, or annum (symbol: a). To this can be added metric prefixes, such as kilo (thousand), mega (million), and giga (billion). So something happening 100,000 years ago would be something which happened at 100 ka; an event 66 million years ago would be at 66 Ma, and something 2 billion years ago would be at 2 Ga. Durations of time use the same units, and it should be clear from context whether the time in question is a duration or a relative time before present.

At the top of this post is the most recently published geologic timescale. This timescale represents the best science available at the time of publication. However, as more evidence is gathered, these boundaries can be shifted around. To most people, the shift in the Cretaceous-Paleogene boundary (the break between the left-most major column and the second) from 65.5 Ma to 66.0 Ma in the newest revision of the timescale doesn’t mean much. However, if you are trying to understand causes and effects near that time period, it can make a big difference!

One major feature to notice about the geologic timescale is that it is depicted in a non-linear fashion. That is, the right-most column (Precambrian) represents 88% of Earth’s history. The Paleozoic represents 6%, and is longer than the Mesozoic and Cenozoic combined. The Cenozoic contains only the last 66.0 Ma, or 1.4% of Earth’s history.

Our ability to tell time for more recent events is better than for older ones: good geochronology has uncertainties between 1% and 0.1% of the age. For something 66 million years old, the uncertainty in age can be around 66 ka or less [2]; for something 2 billion years old, the uncertainty is likely to be closer to 2 million years. A lot can happen in 2 million years!

Getting back to the timescale chart, present-day is at the top left. As you go down the column, you are going back in time. The bottom of the column connects to the top of the column to the right of it. At the bottom of the right-most column is the earliest part of the rock record on Earth. Very little remains of this age which has not been recycled into new rock.

The divisions are made on the basis of major events in Earth history (or on big round numbers for the oldest parts). Many divisions represent shifts in the types of life (often plants or animals) found on Earth. For instance, the base of the Mesozoic is defined by the first appearance of Hindeodus parvus (a conodont, which is kind of like a modern eel) in the fossil record. The defining species tend to be marine, because marine records are usually more continuous, are more likely to be preserved, and have more species found across the globe (technical term: cosmopolitan).

Several different methods exist for determining the age of a rock: radio-isotopic dating, biostratigraphy, and paleomagnetism being the major methods employed. For sedimentary rocks younger than 50 Ma, astrochronology (or orbital tuning) can be used to match climate signals found in the rock to the Earth’s tilt, precession, and eccentricity.[3]

Radio-isotopic dating is the most reliable method.* By measuring how much radioactive decay has happened since a rock formed, and knowing the rate at which the decay occurs, the date of formation can be determined. For volcanic ash deposited in a sedimentary sequence, that formation is roughly equivalent to the eruption date.

Biostratigraphy is used when fossils are present but no suitable material for radio-isotopic dating is available. The appearance and disappearance of various species (again, usually marine species found world-wide) are used to mark time. This is relative, and subject to sampling and preservation biases, but can yield rough answers in places where otherwise there would be no answer at all. However, it is difficult to apply in the Precambrian, because there were fewer, less-complex lifeforms at that time. Most of the diversity of life on Earth post-dates the Cambrian explosion at ~541 Ma. For rocks newer than that, the fossils found within them can give a rough estimate of the age.

Paleomagnetism is used when there are recorded direction changes in the Earth’s magnetic field within a section of rock, and at least some of that rock is fairly precisely dated. By counting magnetic field reversals from a known-age point, the ages of the section in question can be determined by correlation to a well-dated section with the same reversals.

In summary, the Earth is old, and the ages of events are generally known to 0.1-1% precision. The geologic timescale is broken up into smaller parts, and the size of divisions generally decreases as modern time is approached. Units of Ma (mega-annum, million years) are appropriate for much of Earth’s history, with ka used for recent events and Ga used for the oldest parts. As we continue on our exploration of Heard Island and other topics, the geologic timescale will be a very useful tool for understanding how pieces fit together in time.

[1] Gradstein, F.M, Ogg, J.G., Schmitz, M.D., et al., 2012, The Geologic Time Scale 2012: Boston, USA, Elsevier, doi: 10.1016/B978-0-444-59425-9.00004-4.

[2] Renne, P. R., Deino, A. L., Hilgen, F. J., Kuiper, K. F., Mark, D. F., Mitchell, W. S., III, Morgan, L. E., Mundil, R., Smit, J. (2013) Time Scales of Critical Events Around the Cretaceous-Paleogene Boundary. Science 339: 684-687, doi: 10.1126/science.1230492.

[3] Kuiper, K.F., Deino, A., Hilgen, F.J., Krijgsman, W., Renne, P.R. and Wijbrans, J.R. (2008) Synchronizing the 40Ar/39Ar and astronomical clocks of Earth history. Science 320: 500-504, doi: 10.1126/science.1154339.

* Its theory and operation is more complicated than this blog post can contain. I may try to write one later which has much more of the nuance and technical details.

Geoscientist’s Toolkit: Google Maps/Earth

Glass Mountain, Siskiyou County, CA.  Image credit: Google Maps
Glass Mountain, Siskiyou County, CA. Image credit: Google Maps

One of the more useful tools available to a geoscientist these days is Google Maps (or Google Earth). The maps can show where you might want to sample, where interesting geological features are (moraines, lava flows, river deltas, etc.). Overlays show terrain (topography), and roads, to aid you in figuring out how to best access the site.

Satellite images can show larger-scale features which may be fairly easily missed from the ground. Take for example the Manicouagan Crater in Quebec. The ring-like lake is 70 km in diameter, yet from the satellite/aerial imagery looks a lot like a crater.

With Google Earth, placemarks can be used to mark where samples were collected, and notes on the collection can be stored. This makes it very easy to go back later and see the field notes at a glance.

Although I haven’t used Google Earth or Google Maps for anything particularly quantitative aside from distances between sample locations, it’s a pretty useful tool. I enjoy playing around with it, too. There are some spectacular features out there, such as the lava flows of Glass Mountain, seen above. Can you figure out the relative sequence of the flows?

Meteorology and its Application to Heard Island

Cloud vortices off Heard Island. Image credit: NASA GSFC (Terra/MODIS, 9/19/2011 for you satellite imagery junkies).

Meteorology is an important consideration for any outing, be it a trip to the grocery store or an extended expedition. You will prepare differently if the temperature is hot enough to melt butter in the shade than you would if it’s cold enough to flash-freeze a pot of boiling water.

There are two different things we will need to keep in mind for these preparations: climate and weather. Although they are related, they are fundamentally different. Climate is long-term, whereas weather is short-term. For instance, the average high temperature* for Minneapolis for January 4th is 24 F. That’s the climatological average; if you’re planning a trip to Minneapolis for January 4, 2016, that’s a ballpark of what to expect. Weather is more variable, of course. In 2015, the high temperature on January 4th was 12 F; in 2014, it was 35 F. That’s weather. Here’s an analogy: take two six-sided dice. On average, when you roll them, their sum will be seven (that’s the climate). However, you shouldn’t be surprised with a roll of three!

Last month at the Five Thirty Eight blog, Nate Silver did a great job analyzing the amount of weather at various cities across the US, and in general exploring this distinction and the limits of its usefulness. Unfortunately, his title is a bit misleading:

“Which City Has The Most Unpredictable Weather?”

His use of unpredictable has nothing to do with the skills or abilities of the local meteorologists.** Instead, it is a reflection of the variability away from the climate average. That is, if you use the climate average as a forecast, how likely is it to be correct? In some areas, such as Phoenix, AZ, the climate average high temperature is a very good predictor. In others, like Minneapolis, the departures from average can be larger and more frequent, as exemplified above.

So, now that we have that discussion out of the way, and deferring things like uncertainty to another post, what do we know about Heard Island?

Expect cool temperatures, wet weather, and plenty of wind. The vast icy waters surrounding the island keep conditions from changing much. Temperatures remain near freezing year-round, with monthly average temperatures in summer still only 5.2 C (~41 F). The ocean provides plenty of moisture too; a research expedition from 1948-1954 recorded precipitation on 75% of days at Atlas Cove, one of the more accessible parts of the island.

The volcano can make its own weather by disrupting the west-to-east winds. Windward locations tend to see more fog and rain (like the coastal parts of San Francisco), while leeward areas see more sun and warmer temperatures (like Berkeley or Palo Alto). Lenticular clouds, formed when the humid air is pushed up around the mountain, are also found at Heard Island. Other conditions can cause cloud vortices when the smooth flow of wind is disrupted while passing the island, as seen in the picture at the top of this post.

In the southern hemisphere, there is much less land to disrupt the smooth flow of air than there is in the northern hemisphere. Consequently, the winds tend to be stronger more consistent. At Atlas Cove, the average wind speeds are around 26-33.5 km/h (16-21 mph), with gusts recorded up to ~180 km/h (110 mph). That means we can expect damage similar to that found from a borderline EF1/EF2 tornado.***

In short, the climate of Heard Island is near-freezing, wet, and strongly influenced and moderated by the water around it. Be prepared for cold, snow, rain, and wind. There will be some sunshine in there too, but it won’t be the norm.

* The National Weather Service computes this over the 30-year period of 1981-2010.
** Variable would have been a more appropriate word, because devious has deviated from the sense which would be useful here.
*** Tornado categories use the Enhanced Fujita scale (0-5, 5 is strongest), and are estimates of wind speed based on damage. Obviously we’d rather use a direct measurement and have our camp sturdy enough to not have damage to use for estimating wind speed. More on the inner workings of the (enhanced) Fujita scale can be found at the NOAA Storm Prediction Center.

Global Warming, and Stephenson Glacier Retreat

Annual global surface temperature difference from the 20th century average.  2014 is the 38th straight year above average.  Image credit: NOAA.
Annual global surface temperature difference from the 20th century average. 2014 is the 38th straight year above average. Image credit: @NOAA.

Two things came to my attention today which are of particular interest.

First, NOAA has announced that globally, 2014 was the warmest year on record, and the 38th straight year of above-average temperatures. Continued action will be needed in 2015 to reverse this trend. Every delay makes fixing the situation more difficult.

Second, Mauri Pelto has written today about the retreat of Stephenson Glacier and the formation of a lagoon on Heard Island. In 1947-1948, when members of the Australian National Antarctic Research Expedition (ANARE) spent 15 months at Heard Island, they found Spit Point, on the southeast side of the island, was only accessible after crossing Stephenson Glacier. Imagery from LANDSAT shows substantial retreat, as do photographs from a 2004 expedition to Heard Island.

Landsat 2010 image, annotated by Mauri Pelto.  Arrows mark the toe of the glacier in 2001 (purple), 2010 (red), and 2013 (yellow).  Additional images are available on Mauri Pelto's blog.
Landsat 2010 image, annotated by Mauri Pelto. Arrows mark the toe of the glacier in 2001 (purple), 2010 (red), and 2013 (yellow). Additional images are available on Mauri Pelto’s blog.

Today, where once Stephenson Glacier met the ocean, there is now Stephenson Lagoon. The toe of the glacier has retreated inland, and to my eye appears to have moved about 4 km. With a warming at Atlas Cove of 1 °C over 1947-2001, the retreat is not surprising.

On an Island Far Away…

World map.  Image credit: NASA
World map. Image credit: NASA. Click for full size.

In order to better understand the project, and what I will be doing on Heard Island, it is important to know things about the island itself. Perhaps the easiest thing to talk about is where the island is.

Here’s the same world map as above, but now with additional annotation. Shown in partial transparency is the western hemisphere antipodes (opposite side of the world). A red arrow points to Heard Island, and a red circle in Saskatchewan marks Heard Island’s (approximate) antipode.

Red arrow marks location of Heard Island; red circle marks approximate location of Heard Island antipode.
Click for full size. Red arrow marks location of Heard Island; red circle marks approximate location of Heard Island antipode. Adapted from NASA.

As you can see, Heard Island (technically Heard Island and McDonald Islands) is far away from other land, and about as far from Minnesota as one can go without being in space.* There are no airports on the island. Only by sea (or helicopter for the final mile) can we reach the island. For our expedition, there will be no helicopter.

To reach the island, our team will board the Akademik Shokalskiy in Fremantle, Australia (southwest corner, near Perth) RV Braveheart in Cape Town, South Africa. We will then sail southwest southeast through the Roaring Forties and into the Furious Fifties, and about ten days after departure (weather permitting, and in that part of the world it is often inclement) we will arrive.

Heard Island is of a modest size, 20-30 km across (13-20 miles). In the center is a 9000-foot tall volcano, Big Ben, which I will elaborate on in a further post. Mantling Big Ben and flowing down to the sea are glaciers, which cover the majority of the island. In many places, the ice forms sheer cliffs where it enters the sea, making landing on the island difficult.

There is no permanent human settlement on Heard Island. An early research party stayed for fifteen months during 1947-1948 [2], and the most recent winter expedition was in 1992. It is an Australian territory, and home to one of Australia’s two active volcanoes—the other being the smaller, nearby McDonald Island.

Because Heard Island is so remote and has such active surface geology (volcano, glaciers, streams, high wind) and has no permanent inhabitants or introduced species, it has been designated a UNESCO World Heritage Site.[2]** These conditions make the island an excellent natural laboratory to study all sorts of phenomena from climate change to glaciology to biology.*** I’ll have lots more on all that coming up in future posts!

[1] Arthur Scholes, Fourteen Men, E. P. Dutton, 1952.
[2] UNESCO organization. Retrieved January 8, 2015.

* Space is much closer to Minneapolis than Heard Island, or even South Dakota.
** For more on this general topic, the Wikipedia page on the Geography of Heard Island and McDonald Islands is informative.
*** While it is unlike me to paraphrase J. D. Salinger’s Holden Caulfield (from Catcher in the Rye), if you thought it was a somewhat tricky question figuring out where ducks go in the winter, think about where these penguins go in the winter. They do migrate away from Heard Island.[1]

Update 5/14/2015: Vessel and port of departure have changed. More info here (my blog) and here (official).


Welcome to The Inquisitive Rockhopper!

Named after rockhopper penguins, which are naturally inquisitive, the title plays on the author’s affinity to hop about on rocky outcrops admiring the geology.

This draw to neat rocks has extended so far that I am going on the Heard Island Expedition to (you guessed it!) Heard Island in November and December of 2015 March and April, 2016. While there I will do some science—perhaps assisting with a population survey of rockhopper penguins and other birds—as well as lots of ham radio as VK0EK.

On this blog I intend to cover a review of the scientific knowledge so far acquired on or about Heard Island, what I hope to accomplish while I’m there, and what some of the challenges are associated with this expedition. I am also on Twitter as @i_rockhopper.

Update 5/13/2015: Expedition has been rescheduled for March/April, 2016. More info here (my blog) and here (official).