If you live in the northeast part of the United States, guess what?  We are moving south!

Seriously, the northeast part of the continent that contains the United States is slowly drifting to the south.  Well in reality it is going in many different directions but the overall shift seems to be toward the equator.  See the map below to get an idea of what I am saying. The arrows indicate the direction the crust is moving. 

So I am guessing at this point you are wondering how in the world this could be happening? The answer is simple on one level but overwhelmingly complex on another. 

I will give the easy answer first:
The Earth is trying to fix itself after being stepped on for thousands of years. 

And now the more complex answer: 
The last of the massive ice age glaciers, which receded 10,000 years ago, caused the crust of the Earth to compress under their weight. 

Around 110,000 years ago the Earth began to cool and glaciers, or giant and slow moving flows of ice that are created by compacted snow on sides of mountains, took over a huge amount of real estate in the northern hemisphere.  See the map below to understand the extent of the ice sheet that originated at the north pole of the Earth. 

As you can see the glaciers reached their maximum around 18,000 years ago.  Soon after this glacial max a period of warming caused the ice sheet to melt and recede back into the northern part of the hemisphere where it remains (especially in Greenland) today.

Specifically where I live in the Hudson Valley we had the Laurentide Ice Sheet.  Well over a mile of ice was stacked right over where I am sitting while I write this blog!   “The Laurentide ice sheet advanced and retreated over a period of 60,000 years. The last advance reached maximum 22,000 years ago, extending from southeastern Alberta across what are now the Great Lakes to the east coast” (New York Nature).  The Hudson Valley itself was created by the epic forces glaciers exerted to carve out the land beneath them.  In fact there were four different advances and retreats of glaciers during this time in the Hudson Valley.

Each time the glaciers advanced the pushed out the topsoil beneath them.  Ever wonder why New Jersey is called the Garden State?  It is because the glaciers took all of New York’s good topsoil for growing!

The glaciers picked up and pushed the soil to the south and in return deposited the large boulders and stones (glacial till) that we have in the Hudson Valley.  Trying to dig a hole is an hour long process where I live in Ulster County because of the amount of rocks deposited by the ice sheet. 

The glaciers did more than drop rocks and crush the Earth.  During the last ice age the present form of the Hudson River was carved out.  “Near Storm King, there is a place on the Hudson River bed that is nearly 200 feet below sea level. When the glaciers melted and the sea level rose back to normal, these streams and rivers flooded with sea water. The Hudson is in certain places like Norwegian fjords, drowned valleys” (Watertrail). 

I would love to give a number for how much glaciers weigh but after researching I cannot seem to find anything.  What I can tell you is that the pounds per square inch beneath the glacier were most likely in the thousands. 

Some may think that the Earth is too large to be dented but that is not the case at all.  The Laurentide Ice Sheet was so heavy that it crushed the crust and caused it to sag into the mantle!  When the ice melted the crust had to regain its former shape. 

Think of crushing a plastic bottle with your hands.  Your hands are the glaciers and the bottle is the Earth’s crust.  When you remove your hands some areas of the bottle spring back right away simply because there is no longer any pressure.  The other parts of the bottle do not spring back so quickly.  To fix this you have to blow into the bottle to make it pop back into place.   You blowing into the bottle represents the heat and pressure that is pushed onto the bottom of the crust by the liquid mantle inside the Earth.  When the glaciers pushed down the crust beneath them the liquid mantle was pushed out of the way by the weight of the crust above.

If you need to see a visual animation of this process to better understand it please go here. 

Let us go back to the beginning of this blog and return to the original topic- the northeast of the United States moving south.  If you have not been able to figure out why it is moving south, that is okay, because it took me a while to figure it out, too! The reality is the continent is rebounding, even today, since the glaciers left.

Scientists knew about “post-glacial rebound” for years before the measurements presented the fact that the northeast is shifting south.  They were baffled to see this result and immediately tried to explain it. The answer?  It has everything to do with the rebounding process. 

The continent is stretching horizontally as it bounces back from the compression process.  “It turns out this slow recovery is also causing a very small horizontal shift, said Eric Calais, a geophysicist at Purdue University in Indiana. The movement varies from one spot to another, but the overall effect amounts to a 1-millimeter shortening per year of the distance between Florida and the Hudson Bay in northeastern Canada. That's about an inch every 25 years” (MSNBC). 

If you had a balloon and pushed it against the wall it would have to stretch out sideways.  That process is the same one that is happening to the crust.  It is stretching sideways as it is pushed from beneath.

This rebound is not exactly a subtle process.  Many of the smaller earthquakes that occur in the northeast United States are caused by the crust trying to fix itself.  Here is a map of earthquakes in New York from 1990-2006 from the USGS.

The earthquakes around New York City and northern New York were most likely caused by faults, not by glacial rebound.  However the smaller earthquakes across the state were probably caused by the crust suddenly moving as it relaxes. 

In May of last year Maine suffered dozens of microquakes within a matter of days. “All the quakes measured below magnitude 2, and many were too small to feel. Early notification came from residents’ calls to local authorities, reporting the sound of gunshots and unexpected blasting. It was actually the sound of Earth’s crust moving” (Wired). 

When the glacier was sitting on the northeast U.S. the crust was pushed down 500 feet! 

Let me put this in perspective:  My elevation is 155 feet above sea level.  If the glacier was sitting on top of the crust where I am right now I would be below sea level.  If we somehow removed the glacier quickly and allowed the water from the ocean to flow in I would be under the Atlantic Ocean right now!

Conclusion:

The last glaciers in the northeast melted thousands of years ago.  This is a blink of the eye in geological time. The rebound process will continue for hundreds if not thousands of years to come.  The earthquakes will not be huge (over 4.0M) but I can guarantee that there will be hundreds of headlines over the next millennia as the Earth tries to heal the damage that the glaciers caused to the crust. 

Of course if another ice age comes along the crust will have to deal with this ALL over again. 

Don’t worry, though, Earth is used to it.   :-)

Thanks for reading!

- The Weather Dork

Sources:
http://watertrail.org/geology/
http://www.scotese.com
http://www.wired.com/wiredscience/2011/05/maine-earthquakes/
http://www.msnbc.msn.com/id/10498900/ns/technology_and_science-science/t/northeast-moving-south/
http://www.newyorknature.net/IceAge.html
http://www.fccj.info/gly1001/animations/Chapter6/GlacialIsostasy.html
http://www.geo.hunter.cuny.edu/bight/coast.html
http://www.usgs.gov

Last night I posted on Weather Dork an exposure of the night sky in Highland, NY.  See the image below.  

Having trouble seeing it?  It's okay! Here is a more detailed image of Orion, or, The Hunter.  

Orion has been acknowledged by different cultures around the world for thousands of years.  It is one of the most noticeable constellations in the sky due in part to the very thing that makes him famous, Orion's Belt.  

The belt is made up of three individual stars: Alnitak, Alnilam, and Mintaka.  The three stars look like they are right next to one another, right?  I know it may look this way but in reality they are many many light years (or the distance it takes to travel at the speed of light in one year) away from one another.  

Think of it this way.  You are sitting at a table and have three grapes sitting in front of you.  You take the first grape and put it one foot away from you on the table.  The next you put two feet away from you and just to the right of the first.  The final grape you set on the edge of the table on the other side and again just to the right of the other two.  Then, you kneel down and look at the grapes at eye level.  They look like they are right next to one another but in reality they are spread out over a distance.  This is the concept with the three stars that make up Orion's Belt.  

But this blog is not about Orion's Belt, it is about the two massive stars that stand out in it: Rigel and Betelgeuse.  

Let's look at a photo of the two stars to help us understand where they are in the constellation:  

Let's start with Rigel, the smallest of two:

Rigel is the brightest star in the constellation Orion and one of the brightest stars in the night sky.  It is around 850 light years away, or, if you were traveling at 700,000,000mph it would still take 850 years to get to Rigel from Earth.  Earthsky.org puts this in perspective, "In other words, the light you may see from Rigel some spring or winter night, started on its journey at least 250 years before Columbus sailed across the Atlantic!"

The star itself is called a blue supergiant. It literally is a giant! To understand the size of the Rigel we must first understand the size of our own Sun when compared with the Earth.  Look at this image:  

The Earth is just a speck of dust when compared to the star that gives us our light and warmth.  When I first learned about the size of the Sun I was shocked! It's massive! 

Then, I learned about the other stars in the universe.  Check out this image of Rigel when compared to our own Sun, or Sol.  

Rigel is extremely hot and bright, much hotter and brighter than our own star.  In fact Rigel is 60,000 times BRIGHTER than our own Sun! You'd have to wear a welding mask just to be able to function during the day.  Blue supergiants really do live up to their name.  Just like a giant they go through A LOT of food to survive.  Stars eat elements.  Specifically they take elements and fuse them to create light and heat.  Our Sun does this with hydrogen.  It fuses hydrogen to create helium.  However, there is only so much hydrogen to fuse in a star.  

Rigel has run out of fuel and is expanding.  The blue color comes from the temperature it burns at.  The hottest stars are blue and the "coolest" stars are red.  Our Sun is in the middle with a yellow color.  


Here is a close up of Rigel from space:  

Next let's talk about Betelgeuse, Rigel's BIG brother:

Betelgeuse is one of the largest and luminous starts known to the human race.  If it were at the center of our Solar System, its surface would extend past the asteroid belt possibly to the orbit of Jupiter and beyond, wholly engulfing Mercury, Venus, Earth, and Mars.  Betelgeuse is about 600 light years away so the light we see from the star today is 600 years old.   

Remember how I said Rigel was a giant?  Well Betelgeuse dwarfs Rigel! Look at this photo and keep in mind the other size comparisons from above.  

Think of it this way:

If you were to stack multiple Earths inside the Sun to fill up the entire area it would take over 1 MILLION Earths! 

BUT, if you were to fill up Betelgeuse with multiple Suns it would take 1 BILLION SUNS just to fill the inside.  


Now let's talk about the future of these stars: 
Rigel and Betelgeuse represent two very distinctive stages of a star's life.  After a star with more than 10 solar masses, or 10x the mass of our own Sun, burns through its hydrogen it will become a red supergiant.  Betelgeuse is an example of this.  

It takes a lot of fuel to allow a star to continue fusion.  Over time it will try to fuse different elements until it finally tries to fuse iron.  Iron DOES NOT allow fusion.  The result?  

A titanic explosion that will crush the core of the star into a black hole, while blasting the outer layers of the star into space.  This explosion is called a Supernova.  Supernovas shine for months until they finally burn out.  What's left?  An extremely massive neutron star that cannot support itself in space.

Think of it this way.  If you took a spoonful of a neutron star it would weigh 100,000,000 tons!  Eventually some of these stars collapse and form one of the scariest things in the universe, a black hole.  

There are additional calculations and solar masses and difficult astronomy terms that decide which stars go supernova, which stars just burn out, and which stars become black holes but it's confusing.  

I will say that our own star will not supernova.  The Sun, around 5 billion years from now, will grow to the size of a giant and engulf the Earth as it tries to fuse different elements.  Eventually it will run out of fuel and shrink/cool into a white dwarf.  Over time this white dwarf will cool and dim into a black dwarf.  Black dwarfs are theorized to become giant diamonds.  If you find yourself in space look for giant diamonds floating around! 

In conclusion, well, there's not much to say.  The Universe is a truly amazing and violent place where unimaginable explosions and births happen every single day. Betelgeuse may have already gone supernova 100 years ago.  It will take another 700 years for the light to reach us.  A supernova's light is bright enough to make night as bright as day on planet Earth.  It will last for months until it stops and Betelgeuse is gone from the night sky.  This is the cycle of the stars.  I could go on and on for hours discussing the beauty and power held without our universe but I will stop here, for now.  I hope you enjoyed this blog.  As always please feel free to comment.  

Sources:

Aside from the images and one quote which are cited I used my own knowledge of Astronomy to write this blog.