3-Feb Iceberg Ahoy
The sea is calm again but with a big rolling swell. Outside the temperature is still dropping. It’s below zero today and the sea temperature is just below one degree. A light snow is falling and we now have to wear full cold weather gear if we wish to venture out on deck. This includes the thick felt gumboot liners, at least two or three pairs of gloves, and thermal underwear.
We find out at breakfast that the “Iceberg ahoy!” call came from the bridge watch at 0200 hours. Our powerful iceberg searchlights picked up the first decent sized iceberg, about the size of a house. The latitude of the sighting is 64 south and the winner is Ed, I think.
We guessed that 64 in French must be something like “Soixante Quattro” so at our morning toolbox meeting our little mascot penguin gets told of his new name. (Better find someone on board who can speak the French lingo to make sure we spell it properly). But our little mascot didn’t like his new name and would rather be called “SQ” for short instead.
Lindsay, the second engineer, hollers me from down below at 0930 hours - ”Iceberg, iceberg”. I charge out on deck for my first encounter with an iceberg.
Outside it feels like Christmas, lightly snowing and in the grey gloomy mist is my iceberg. This ice block looked huge to me, about the size of a house but apparently it was a little one. Lindsay made me take a photo of it, being my first one; I’ll remember this one he said. As it was too small to warrant a name by the NIC (National Iceberg Centre), I decided to officially name it AM01 (my initials and my first one). A fascination for icebergs was to be born this day and I started to learn about these magnificent pieces of natural sculpture. I discovered that they are timeless but living works of art.
An iceberg actually begins as snow. Originally conceived millions of years ago in the middle of Antarctica, it snowed and this snow formed a granular laver called ‘neve’. This is compressed to denser ‘firn’ and as even new layers fall on top, the firn gets compressed yet even further, forcing out more air bubbles. Pure Glacial ice is 200 times denser than fresh snow. In fact the complete layer of ice is so thick and the weight so heavy that it depresses the whole continent by 1km.
The build-up of ice over Antarctica is like a giant pancake, and the ice becomes fluid like very slow moving treacle and it so journeys to the sea in a glacier. When the glacier meets the coast it either enters one of the ice shelves or forms and ice tongue out into the sea. At the seaward end of the glacier or ice shelf, the ice, being lighter than seawater, starts to hinge and gets worked on by tidal and storm action. This action causes large chunks to break off, called ‘calving’ and so icebergs are born and set free to the sea to be continually sculptured by nature into beautiful new forms.
Icebergs form mostly during the spring and summer, when warmer weather increases the rate of calving. An iceberg floats because it is less dense than water, the density of pure ice is about 920 kg/m³, and that of sea water about 1025 kg/m. Thus usually 7/8 of a new iceberg is underwater with the most dense and heaviest part of it being the core. When the lighter top including more recent snow gets washed off, it becomes even denser and as little as only 1/10 it might show above water.
An iceberg can live for many years and during its lifetime, it can tumble and upturn many times as its centre of gravity changes due to the underneath part being sculptured by the sea. 93% of the world's mass of icebergs is found surrounding the Antarctic and if it all melted, it would raise the sea levels by 60 meters.
ICEBERG SHAPE CLASSIFICATION
Officially there are two basic types of iceberg forms: ‘Tabular’ and ‘Non-tabular’.
Tabular: An iceberg with steep sides and flattop. Most Antarctic icebergs start off as tabular and this is the shape that they are in when they have just broken off from a glacier or an ice shelf.
Non-tabular: Describes all other icebergs that are not tabular. This category is further subdivided to include the specific shapes described below. If no other description applies, the iceberg is simply referred to as a non-tabular but we are free to invent new names for these if we want to.
Non-tabular Iceberg Shape Classifications
Blocky: Basically small tabular icebergs. An iceberg with steep, vertical sides and a flat top. It differs from tabular icebergs in that its shape is more like a block than a flat sheet.
Dome: An iceberg with a rounded top. This includes the policeman’s helmet shaped one we saw.
Pinnacle: An iceberg with one or more sharp peaks.
Wedge: An iceberg with a steep edge on one side and a slope on the opposite side.
Dry-Dock: An iceberg that has eroded so that a slot or channel is formed. The castle-like icebergs we saw would probably fit into this category.
Interestingly, the amazing forms of icebergs encountered are not due to melting from the top but instead due to erosion by the warmer seawater underneath. Wave action can erode out magnificent caves at sea level and gradually as this happens the iceberg gets lighter and slowly rises. While this erosion is occurring from below, the top has remained relatively still in tack and the center of gravity subsequently shifts. The iceberg then reaches a point where it becomes unbalanced and, with a thundering crash, topples over. They may then for the first time reveal and show off the magnificent freshly sea sculptured forms.
This sculpturing and topsy-turvy action can happen several times during the life of an iceberg.
As well as shape description an iceberg is further classified by its size as follows.
Growler– less than 1m high & 5m long (named by early sailors who often heard a growling as hey bob in the water)
Bergy Bit 1-4 m high & 5 – 14m high
Small 5-15m high 5-14 m long
Medium 16-45m high 61-122 m long
Large 46-75m high 123-213 m long
Very Large Over 75m high Over 213m long
The sea is calm again but with a big rolling swell. Outside the temperature is still dropping. It’s below zero today and the sea temperature is just below one degree. A light snow is falling and we now have to wear full cold weather gear if we wish to venture out on deck. This includes the thick felt gumboot liners, at least two or three pairs of gloves, and thermal underwear.
We find out at breakfast that the “Iceberg ahoy!” call came from the bridge watch at 0200 hours. Our powerful iceberg searchlights picked up the first decent sized iceberg, about the size of a house. The latitude of the sighting is 64 south and the winner is Ed, I think.
We guessed that 64 in French must be something like “Soixante Quattro” so at our morning toolbox meeting our little mascot penguin gets told of his new name. (Better find someone on board who can speak the French lingo to make sure we spell it properly). But our little mascot didn’t like his new name and would rather be called “SQ” for short instead.
Lindsay, the second engineer, hollers me from down below at 0930 hours - ”Iceberg, iceberg”. I charge out on deck for my first encounter with an iceberg.
Outside it feels like Christmas, lightly snowing and in the grey gloomy mist is my iceberg. This ice block looked huge to me, about the size of a house but apparently it was a little one. Lindsay made me take a photo of it, being my first one; I’ll remember this one he said. As it was too small to warrant a name by the NIC (National Iceberg Centre), I decided to officially name it AM01 (my initials and my first one). A fascination for icebergs was to be born this day and I started to learn about these magnificent pieces of natural sculpture. I discovered that they are timeless but living works of art.
An iceberg actually begins as snow. Originally conceived millions of years ago in the middle of Antarctica, it snowed and this snow formed a granular laver called ‘neve’. This is compressed to denser ‘firn’ and as even new layers fall on top, the firn gets compressed yet even further, forcing out more air bubbles. Pure Glacial ice is 200 times denser than fresh snow. In fact the complete layer of ice is so thick and the weight so heavy that it depresses the whole continent by 1km.
The build-up of ice over Antarctica is like a giant pancake, and the ice becomes fluid like very slow moving treacle and it so journeys to the sea in a glacier. When the glacier meets the coast it either enters one of the ice shelves or forms and ice tongue out into the sea. At the seaward end of the glacier or ice shelf, the ice, being lighter than seawater, starts to hinge and gets worked on by tidal and storm action. This action causes large chunks to break off, called ‘calving’ and so icebergs are born and set free to the sea to be continually sculptured by nature into beautiful new forms.
Icebergs form mostly during the spring and summer, when warmer weather increases the rate of calving. An iceberg floats because it is less dense than water, the density of pure ice is about 920 kg/m³, and that of sea water about 1025 kg/m. Thus usually 7/8 of a new iceberg is underwater with the most dense and heaviest part of it being the core. When the lighter top including more recent snow gets washed off, it becomes even denser and as little as only 1/10 it might show above water.
An iceberg can live for many years and during its lifetime, it can tumble and upturn many times as its centre of gravity changes due to the underneath part being sculptured by the sea. 93% of the world's mass of icebergs is found surrounding the Antarctic and if it all melted, it would raise the sea levels by 60 meters.
ICEBERG SHAPE CLASSIFICATION
Officially there are two basic types of iceberg forms: ‘Tabular’ and ‘Non-tabular’.
Tabular: An iceberg with steep sides and flattop. Most Antarctic icebergs start off as tabular and this is the shape that they are in when they have just broken off from a glacier or an ice shelf.
Non-tabular: Describes all other icebergs that are not tabular. This category is further subdivided to include the specific shapes described below. If no other description applies, the iceberg is simply referred to as a non-tabular but we are free to invent new names for these if we want to.
Non-tabular Iceberg Shape Classifications
Blocky: Basically small tabular icebergs. An iceberg with steep, vertical sides and a flat top. It differs from tabular icebergs in that its shape is more like a block than a flat sheet.
Dome: An iceberg with a rounded top. This includes the policeman’s helmet shaped one we saw.
Pinnacle: An iceberg with one or more sharp peaks.
Wedge: An iceberg with a steep edge on one side and a slope on the opposite side.
Dry-Dock: An iceberg that has eroded so that a slot or channel is formed. The castle-like icebergs we saw would probably fit into this category.
Interestingly, the amazing forms of icebergs encountered are not due to melting from the top but instead due to erosion by the warmer seawater underneath. Wave action can erode out magnificent caves at sea level and gradually as this happens the iceberg gets lighter and slowly rises. While this erosion is occurring from below, the top has remained relatively still in tack and the center of gravity subsequently shifts. The iceberg then reaches a point where it becomes unbalanced and, with a thundering crash, topples over. They may then for the first time reveal and show off the magnificent freshly sea sculptured forms.
This sculpturing and topsy-turvy action can happen several times during the life of an iceberg.
As well as shape description an iceberg is further classified by its size as follows.
Growler– less than 1m high & 5m long (named by early sailors who often heard a growling as hey bob in the water)
Bergy Bit 1-4 m high & 5 – 14m high
Small 5-15m high 5-14 m long
Medium 16-45m high 61-122 m long
Large 46-75m high 123-213 m long
Very Large Over 75m high Over 213m long
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