The Earth Story

This is a drone video of the landslide that occurred in Alta, Norway earlier this week. No one was hurt, and even a dog was rescued after it was able to swim back to shore.

This type of slide is thought to occur on a "Quick Clay" layer, produced as the glaciers departed at the end of the last glaciation. 15,000 years ago - Norway and Scandinavia were covered by a gigantic ice cap. The weight of this ice cap actually pressed down the Earth's crust - like using your hand to push a toy down to the bottom of the bathtub.

When the glaciers melted, the ocean returned, flooding the land you see above the water today. Those ocean waters deposited thin layers of clay and salt on the newly-submerged landscape. But, as the weight of the glaciers was also removed, the land began popping up, bringing this thin layer of ocean sediments above the surface. For the last 10,000 years, sediment from the land buried this thin clay layer, and now houses are constructed on some parts of that landscape. Today, it sometimes only takes a small event, like a rainstorm that dissolves some of the salt, to make that clay layer weak enough to trigger a slide.

-JBB

Dog sledding beneath the dark night skies of Scandinavia over the week of Christmas

Fossil meteorites

This rock is pretty darn awesome.

Thorsburg quarry in Sweden is, for the most part, a standard limestone quarry. It digs into a big unit of limestone, deposited about 480 million years ago when the land that is now Scandanavia was submerged beneath a shallow, tropical ocean. The unit is called the Orthoceratite limestone; it contains some fossils and is used as ingredients for building materials. But, decades ago, several strange rocks began being found within that unit. You’re looking at one.

It took a few decades to figure out what they were, but eventually it was realized that these are meteorites. Buried within this nearly-half-billion-year old limestone, you can find rocks that came to Earth from space. Legitimate fossil meteorites.

The rocks are all of a type called an L-Chondrite. The type itself might not be that interesting, it says things about their chemistry, but the weird thing is, they’re all the same rock type.

When we look at meteorites today, all sorts of different varieties are found. A single meteorite could have originated on one of hundreds of large bodies that formed early in the solar system; having all the meteorites have the same chemistry testifies to them all coming from the same body.

The only way this could happen is if there was a single asteroid that broke up at around this time, probably due to a giant collision within the asteroid belt. The breakup of the L-Chondrite parent body, 480 million years ago, caused a meteor shower on Earth big enough to leave remnants that we’re finding in limestone hundreds of millions of years later. I think that’s pretty awesome.

This particular specimen is owned by Chicago’s Field Museum. The rock is a few cm across, slightly larger than a golf ball (Hey Field Museum, you gotta include a scale bar in press photos!).

-JBB

Image credit: Field Museum http://www.nbcchicago.com/news/local/Field-Museum-adds-rare-meteorites-to-collection--263854301.html

Read more: http://www.geo.tu-freiberg.de/oberseminar/os07_08/ThomasMueller.pdf

raunokoivunen

-River on the border between Finland and Norway starting to freeze for the season

Despite the Solar Minimum, the night skies over the northern hemisphere in September produced some spectacular displays of the northern lights. This videographer presents the September Auroras over Finland.

Original caption:

Snowy Sweden

Aerial cinematography over forests, beaches, fields of flowers, and fjords in Finland.

Pining for the fyords? These landforms are born of ice and water. Back in the ice ages, miles thick sheets of frozen water covered Scandinavia, flowing into a glacial sea. As the ice melted, two opposing forces contended to shape the modern landscape. The sea level rose some 130 metres, drowning many river valleys worldwide, such as Sydney harbour and the Rio de la Plata estuary. Where the ice had been though, the land started to rise in response to the disappearance of the weight, which had been pushing the whole crust downwards into the asthenosphere, a process that continues to this day. Geologists were surprised to discover in the late 18th century that carved sea level markers a couple centuries old and harbours were seen to have somehow risen. It took some time for Louis Agassiz's glacial theory to be accepted, but eventually the combination of events that had shaped this land came to be understood. Loz Image credit: Air Pano.

Scandinavian Crust

This is an absolutely spectacular shot of several stages of crust formation from Kosterhavet National Park in Sweden.

The oldest rocks in this area are highly metamorphosed sedimentary rocks. They are the dark and white, wavy-interfingered rocks. Those rocks started off as sediments and then were caught up in one of several orogenies, or mountain building events, that occurred between 1 and 2 billion years ago.

The sediments are 1.7 billion years old. They were deposited in a basin and then rapidly incorporated in a growing mountain range where they were buried and heated. The heat at the bottom of the mountain range was enough that the rocks began melting. The dark part is metamorphosed gneiss that reached the upper part of the amphibolite facies; the light part is felsic minerals that melted out of the sediments and basically formed a granite. This type of high grade metamorphic rock, heated to such a high grade that they begin melting, is called a migmatite.

This migmatite is cross-cut by a dolerite dike. Dolerite is a term for a mafic, basaltic igneous rock that has slightly crystallized. Basalts are low viscosity and high temperature, so if basalt is trapped underground in a dike it starts to form tiny crystals. This slightly crystalline rock is called a dolerite, or a diabase elsewhere in the world.

Sweden represents at least 2 characterized orogenies, the Gothian orogeny starting about 1.7 billion years ago and the Sveconorwegian Orogeny from about 1.3 to 0.9 billion years ago. These orogenies probably represent continued subduction along the coast of Baltica. This long-lived subduction built mountain ranges, sent magmatic rocks like the dolerite from the mantle up into the crust, and eventually culminated in the assembly of the supercontinent Rodinia.

-JBB

Image credit: Thomas Eliasson of Geological Survey of Sweden https://flic.kr/p/8PadbZ

References: http://foreninger.uio.no/ngf/ngt/pdfs/NGT_79_1_047-056.pdf http://bit.ly/2tgvk1y