It's All in the Waves

      Today's post is pretty much a follow up on yesterday's.  I went from a report on a hundred year old Lake Superior shipwreck just found, to going over other Great Lakes shipwrecks, and related storm damage.  I wanted to explain why the shipwrecks are so devastating during Great Lakes storms. 
      As the title of the post says, it's all in the waves.  Although looking across one of the Great Lakes pretty much looks the same as looking across an ocean the waves are completely different.  An ocean is thousands by many thousands of miles across.  You can't tell that standing from shore, because the circumference of the earth doesn't let you see past twenty miles (that's why it looks the same looking out over Lake Superior or one of the other Great Lakes - I've never been there, but I'm sure that looking across Lake Winnipeg or Lake Manitoba would give the same effect).  Not only do oceans have unbelievable amounts of surface area, but they are several miles deep as well. The Marianas Trench is about 8 miles deep.  That is some unimaginable volume.  The deepest part of Lake Superior, by comparison, is a little over 1300 feet, while the average depth is about 500 feet.  Lake Erie is very shallow by comparison to Lake Superior, and even the other Great Lakes, which have an average depth around 200 to 250 feet. 
      That much volume of water makes it behave in certain ways.  Waves of course are bigger and have a much wider arc.  Prevailing westerlies prevail, and the oceans are susceptible to the tidal forces of the moon and the sun.  Even big Lake Superior has no noticeable tide, and the winds blow across it from any direction.  Being so much shallower by comparison, the wave never reach the size or arc that they do on the oceans.  The biggest they get is about 20 feet high, and sometimes 30 feet have been reported, but that is only in storms.  20 feet is what you get on a "nice" day in the oceans when the "surf's up."  
      When you get waves that high in the Great Lakes they are more choppy.  They are still fairly narrow, compared with an ocean wave.  They still have a narrow arc.  They just get taller during a storm, but not much wider.  
      Think of your favorite fishing lake.  When you go out in your little 15 to 20 foot boat, and the winds pick up, the waves become very choppy.  If they hit your boat from the side, it has the tendency to want to roll.  When you steer your boat into the waves you hear and feel a big slap with each wave.  It is because of the shallowness of the lake the waves get taller, but not much wider.  
      The results of this principle can be seen in the pictures below. 

      An ore freighter on one of the Great Lakes on a normal day.  On an ocean on a normal day it looks pretty much the same. 

      On an ocean during a storm, the waves are huge, and often many times the length of a ship.  They ride within the waves going up them, over the peak, and back down again.  This is when many people get seasick and things roll all over in the galley and everywhere else.  Every time they hit the peak of the wave, it washes over them.  

      Lake Superior (or other Great Lakes) during a storm.  The waves get much bigger, but don't grow as wide as they do tall.  The result is that wave slapping phenomenon.  The waves slap the ship when they hit it, and then wash over.  Worse than that, in the bigger storms the ship is actually suspended between two waves.  Ships are not meant to be carried like that.  It doesn't do to well for their structural integrity.  

      The result of this stress, especially when repeated for wave after wave, is that the ship "breaks her back."  This is what happened to the Edmund Fitzgerald.  It has also happened to many other ships.  During the great storm of 1913 when the Henry B. Smith went down, many of the ships that were lost had their "backs broken."  The same thing happened to many of the ships that were lost during the storm that destroyed the S.S. Mataffa.