What is the density of an iceberg?

Answer 1

The density can vary not only from iceberg to iceberg but also within the iceberg. Let me explain, there is a process to how a glacier forms. Take for instance snow, as it accumulates, it begins to pack due to increasing weight. The deeper snow becomes more like sand. As more and more snow accumulate on the surface, the lower levels undergo increased pressure. At a certain point, the pressure causes the sand like ice to recrystallize. This has nothing to do with melting but solely pressure. keep in mind that glaciers can grow to be several thousand feet deep. This causes tremendous pressure on the lowest levels of the glacier. It's like placing a mountain on top of bed of sand, in no time you end up with a very compact sandstone. In the case of the glacier, the tremendous pressure can cause the ice to recrystallize several times. Each time becoming more dense. Keep in mine, the deeper ice deposits will be under more pressure than the higher ones. This leads to a greater density of the ice at the bottom and decreasingly less dense ice with altitude to do less and less pressure.

Now to icebergs... these are simply pieces of the glacier that have broken off. Depending on how much pressure was exerted on the ice, the density of the bottom of the iceberg can even be greater than the density of water. Notice that icebergs are commonly pear-shaped with the largest diameter furthest below the surface. This is the most dense part of the glacier. The upper part, or tip, is less dense. There are a number of factors that play into this but lets not go there right now. A simple test you can do to prove this is to freeze a piece of ice and shape it in the form of a typical iceberg, place it in a salt water solution and notice what happens, it does just the opposite of what an iceberg does, the larger end will surface and the tip will be submerged. Also notice that it floats at the surface. This is due to the density being normal for fresh water ice which is somewhat less than the density of water.

Remember pressure causes compaction and compaction increases density. Imagine an ice sheet a couple thousand feet tall sitting on bedrock and just how much pressure that ice sitting on the bedrock is undergoing. Its the same concept as the inner core of the earth. The temperature is much greater than the outer core and yet is is a crystallized solid made up of mostly iron. Pressure alone can turn liquids into solids as well as gasses into liquids. Also keep in mind that the freezing point of salt water is lower than that of fresh water. This means you can have an iceberg of fresh water sitting in a "bath" of very cold salt water, cold enough to keep the iceberg from melting. As for the upper part of the iceberg, it will undergo weathering processes just the same as exposed rock. Wind and rain will decompose the surface of the iceberg to more of a point, leaving the base intact. Under the right conditions, you can have the top of an iceberg waste away or break off and the bottom (more dense) section sink to the floor of the ocean. Although pressure is the main contributary for the greater density found in the lower levels of glacial ice sheets, temperature also plays a roll in what crystal forms the ice takes. The process is much like that of the creation of igneous rocks only instead of heat and pressure, you have cold and pressure.