Tuesday, March 5, 2013

All About Ice Volcanoes and more

When I talk with people who are visiting the Lake Superior shoreline for the first time in the winter, I always inform them of the danger of venturing out onto the shore ice.  When shore ice develops on Lake Superior in early winter, ice volcanoes develop along the leading edge of the forming ice. Waves that roll into shore from deeper water rise up as they hit the shallows, causing water to spout up through cracks in the newly formed ice. This wave action creates the characteristic cone shape of the ice volcano.  Subsequent waves, driven by strong onshore winds, continue to travel underneath the ice and are forced up through cracks and previously formed cones.

The height of cones can vary from two feet to more than 30 feet.

Technically these ice volcanoes are called cryovolcanoes.  These are "volcanoes" that erupt volatiles such as water, ammonia or methane, instead of molten rock.   The substances erupted from these cryovolcanoes are usually liquids and form plumes, but can also be in vapour form.  After eruption, cryomagma condenses to a solid form when exposed to the very low surrounding temperature. Cryovolcanoes form on icy moons as well as on the shores of ice covered lakes.

To form ice volcanoes, the following conditions must exist:

1. Onshore winds must be sustained causing waves to be higher than three feet tall.
2. Ambient air temperatures must be below freezing.
3. There must be shore ice that has already formed, creating a thick ice shelf that extends off shore.
4. Wave energy must be concentrated into a concentrated area so that the splash can, over time, cause a cone to form. Irregularities along the leading edge of the shelf help concentrate wave energy into larger waves, thus creating taller ejections of spatter. It is at the irregularities that ice volcanoes typically form.
5. Cones at the leading edge of the ice shelf are initially open to the water.  However after the ice shelf builds away from the volcanoes, the cones remain active and become completely enclosed. Wave energy beneath the ice forces water up through cracks, openings and previously formed cones as the wave feels bottom.
6. If there are sandbars offshore, such as those off shore in Grand Marais, the dynamics of the sandbar are also conducive to cause ice volcanoes to form.

Sometimes a whole row of ice volcanoes form.

Below is a picture from the Internet, showing a partially destroyed ice volcano that displays the internal structure.
Below are some more pictures I took on the beach yesterday. 
The series of photos below zoom into the lighthouse at the end of the break wall.
The first row of ice marks the actual shoreline.
Patterns in the snow...


1 comment:

  1. These pictures are beautiful! Thanks for sharing.