Thursday, July 30, 2015

For the love of lava: Adventures on Tolbachik volcano

-Janine

Last month I had the amazing opportunity to do field work on Tolbachik volcano in Kamchatka, Russia. I spent a week on one of the lava flows produced during the 2012-2013 eruption and was blown away by the formations and textures that the flowing rock can create. Here are some of the features that caught my eye while I was coming to the realization of just how awesome basalt can be. I'm sure you can imagine the molten rock flowing and fracturing, then oozing out when the opportunity presents itself.

NASA Advanced Land Imager (ALI, on the Earth Observing-1 satellite) false color image showing the hot lava flow on December 1st, 2012. Image courtesy of the NASA Earth Observatory.
View of the main Tolbachik complex from camp, right next to the lava flow.




This tongue of lava formed a solid shell then the still-fluid lava inside cracked it open so it could keep moving forward.
Not too far under the crust is a bright oxidation discoloration - this tells us that it was hot! But we already knew that. This lava is crunchy to walk on and looks a lot like tree bark on the surface.
This area of lava produced folds as the surface was a little more solid than the flowing lava underneath. After this had formed the lava inflated and deflated (probably multiple times) breaking up the lava into this very sharp, very difficult to walk over lava hazard. Tolbachik is in the background.
This one reminded me of the New Zealand Koru design. There is a bit of home everywhere.
Here the solid lava surface cracked open and more fluid lava tried to squeeze upward through the fracture. Foot at the bottom for scale.
I like how this image inspires thoughts of Nightmare on Elm Street.
These are lavacicles (not a technical term) that formed by dripping lava in the top of a lava tube once the lava flowed through and emptied.
The gasses in the lava met up and joined these vesicles (holes left by the bubbles), then they were stretched as the lava was flowing. You can see different areas of folding through the lava.
This discoloration caught my attention! It was like an oil slick on the surface of the flow (clearly was not an oil slick).
This little hole (~15 cm across) is actually a doorway into a very hot (>500 degrees C) lava tube. We were drawn to it by the obvious hot air and roaring sound coming from it. Upon throwing rocks in (from a safe distance!) we didn't hear them hit the ground.
This is a classic 'ropy' texture of pahoehoe lava.
This stuff is SHARP! When lava cools quickly it is very glassy, hence the gloves.
The lava surface can have a large amount of detail and different colors.
Skylight - a hole that formed over a lava tube.
Steam is still flowing through cracks from the hot lava beneath.
Panorama of the lava flow (there is another one from the same eruption behind me) taken from one of Tolbachik's many scoria cones. You can see the different smooth (pahoehoe) and rough (a'a') lava. Tolbachik is in the upper left with the extinct Udina volcano to the right.

I have always been more of an explosive volcanologist - excited more by pyroclastic density currents and explosive eruptions. Tolbachik has opened my eyes to how fascinating and complex basaltic lava is. If you get a chance to check out a lava flow, take very sturdy and tough boots, tough gloves, and long pants to keep yourself safe. Always be very careful, as you can see there are a lot of hollow places under the glassy crust and it can have fracture networks waiting to break. Although there are hazards with every aspect of volcanoes, as we can see here, there is also great beauty. I hope these images have ignited your imagination and inspired a love for lava.






Friday, July 24, 2015

Quick tour of the urban geology of Rome

I just returned from two, very warm, weeks in Italy. The group wanted to go somewhere with volcanoes and good food, so Italy was a natural choice. While Italian geology is fascinating in its own right, that will have to be saved for a different post. Today's post is a bit of urban geology.  I found that I spent most of my time in Rome looking at the building stone, and took mostly pictures of rocks and stone. The Romans collected the most beautiful stone from their empire and then used to make buildings and show off their wealth. These stones were then scavenged from Roman sites to build the next round of impressive buildings by the Catholic Church. So when you tour buildings in Rome it includes a geologic tour of the whole Mediterranean.
While most visitors expect Rome to made of endless white marble there are a range of stone types from around the far reaches of the Roman Empire.
One of the classic stone types used to impress visitors is this deep red porphyry from Egypt. Porphyry is a crystal-rich igneous rock and is where we get the term porphyritic (for rocks with some large and some small crystals).
This stone was reserved for the most important monuments and people because of its color. 
The stone that impressed me most was the many colored breccias. A breccia is broken rock that has been cemented back together naturally. The color of the clasts and the cement can be vibrant and contrasting and make for some impressive pieces.

Many of the most famous breccias originated in Turkey.




 

Some of the multicolored stones have a metamorphic origin. Rather than being separate pieces of stone that were stuck back together, this gneiss (pronounced nice) was a solid piece of rock that was put under great pressure and heat to deform it.

In metamorphic rocks some of the elements moved from their previous crystals to form new crystals (like the big pink one) and give it a whole new texture.

Other stones have a complicated history. This one may have been a breccia that was later heated and squished (metamorphosed).

These crystals have dissolution textures on their edges which suggest that they were in contact with hot fluids (or melt) that were different than the one they formed in.
There were also many pieces made out of agate. Agate forms by the growth of minerals (silica) inside some sort of crack or void in a volcanic rock.
  

There were also lots of different types of granite. Despite what your counter top may be made of, granite is an igneous rock that is made up of large crystals of similar sizes. The composition of granite is high in silica, so you get lots of quartz and feldspar.
The abundance of the pink mineral (potassium feldspar) means this column likely came from Egypt.


There was also lots of diorite. Diorite has a similar texture to granite, but has less silica, so different minerals.
My favorite rocks though, were all local. The cheapest building materials will always be what is nearby, so you will find the base of many of the Roman (and pre-Roman structures) were all made out of local volcanic rock.

Pompeii was made with a combination of basalt bricks and blocks, clay brick, and tuff.

A tuff is a rock made of pyroclastic material (ash, pumice, crystals and bits of broken rock) that has become lithified (i.e. is now a rock). The types of rocks I study are usually tuffs so I couldn't help but take photos of lots of them.

I found tuff at the bottom of the Colosseum, in the Roman Forum, Pompeii, Herculanium, old Greek theaters in Sicily and in modern banks and gelato shops.
Residents of Pompeii also used basalt (lava) to pave their streets. This image is of a cross walk in the streets of Pompeii. The modern cities of Sicily still use basalt blocks, but they use paint for the cross walks.


Any stone can be used to make a wall, and here are some pieces of scoria mixed with some chunks of coral.
The white squares are crystals, the brown clast is scoria and the black is a patina from ~2000 years of people and weather touching this piece of the Colosseum.
The tuffs are mostly the deposits from pyroclastic flows. They form during explosive eruptions where hot gas and debris (the ash, crystals and pumice) move down hill at high speeds. Flows like this are what buried Pompeii. This image is of some of the 79 AD deposit that covered Pompeii. This material is not as lithified (still unconsolidated) so it was possible to excavate the city.


 My visit to Rome was an excellent chance to see layers of human history exposed all in one place (Greek, Roman, Medieval, Modern). It reminded me very much of the layers of rock that we use to reconstruct the history of the Earth. Seeing the walls made out of pyroclastic material in Pompeii and the pyroclastic material that buried it was a stark reminder that we have a lot to learn still about this planet, and the clues are so often right in front of, or below us.



Friday, July 3, 2015

The Ant Hill Advantage



-Alison

So for the last two weeks both Janine and I have been off on separate field adventures. This is not uncommon for geologists in the summer. School ends and we dash off for locations with rocks we cannot get at home. I plan on doing a longer post on the cool things I observed about the insides of old eroded volcanoes soon, but not just yet as the travels are not done!


Ant hill made up of volcanic minerals from the Hopi Buttes Volcanic Field, Navajo Nation, AZ, USA.
I did want to share a fun factoid about how ants help geologists when searching for specific rock types by using some examples from my recent field work. Whether or not you had an ant farm as a kid, its pretty easy to imagine the process involved in building an ant colony. The ants excavate tunnels underground and move the material from their tunnels to the surface. This material, moved grain by grain, adds up and can form a hill. As the ant colony gets larger, they bring up material from deeper underground. This helps geologists because it brings minerals to the surface that may be just out of sight. Because we live on a planet with weather (yay atmosphere!) and liquid water, the surface is constantly changing. The ants kindly bring up minerals and rocks that were buried by soil, wind blown dust, or plants and let geologists know where to look.

For example, in the Hopi Buttes Volcanic Field in the Navajo Nation, AZ, USA the deposits contain a lot of pyroxene. The old volcano insides (dikes, diatremes, etc.) stick up as obvious buttes, but the edges of these rocks are worn down and this makes it hard to figure out just how big the volcanic plumbing system was.
Buttes of black volcanic rock surrounded by red sand and siltstones of the Chinle Formation in the Hopi Buttes Volcanic Field.

To figure out where the contact between volcanic deposits and the old host rock is (in this case, sandstones and siltstones) we could use the ant hills to get a better idea of what rock was below us even in flat areas. If the hills were shiny and black, they were digging in the volcanic rocks! If they were red or pink, those were host rocks. We still dig holes to check, but they give us a head start.
Concentration of pyroxene crystals and small pieces of lava in an ant hill.

Another example was from the Dotsero Maar in Colorado, USA. We were tracking the ash deposits from the eruption (possibly as young as 5,000 years ago, making it the youngest eruption in Colorado). Ash quickly turns to soil and gets covered in plants and other debris. To check the location and thickness of the ash we needed to dig lots of holes. Kindly, ants brought up lapilli (pebble sized pieces of scoria) in areas where there were ash deposits and helped us to know where to dig. As digging in 100 F heat is hard work, we appreciated any advantage we could get.


Digging for ash deposits. We could use the ant hills full of lapilli to know we were in a good spot.

There is actually a long history of geologists using ant hills to find minerals when prospecting. And even one case where other prospectors were known to plant minerals to trick their competitors into following false trails! If you want to read a neat book about prospecting, with proper credit to ants, I suggest Barren Lands which is a good way to learn about kimberlites and diamond mining.

Next week I'm off to Italy, so that will mean even more photos and stories to share later this summer.