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The remaining questions is: Why are glaciers then not always blue? As we know, many icebergs (and snow) are white.

The key here is bubbles"bubbles". The reason is that for each ice/air interface, part of the light gets reflected and only a fraction goes through. Therefore the greater the number of bubbles a piece of ice has, the less light will be able to proceed deeper into the ice. As such, when you view light from more bubbly ice, most of it will have traveled through less ice, and thus have had less distance to obtain the blue tint. I've made this figure to help understanding the idea: light in ice with bubbles diagram

The remaining questions is: Why are glaciers then not always blue? As we know many icebergs (and snow) are white.

The key here is bubbles. The reason is that for each ice/air interface, part of the light gets reflected and only a fraction goes through. Therefore the greater the number of bubbles a piece of ice has, the less light will be able to proceed deeper into the ice. As such, when you view light from more bubbly ice, most of it will have traveled through less ice, and thus have had less distance to obtain the blue tint. I've made this figure to help understanding the idea: light in ice with bubbles diagram

The remaining questions is: Why are glaciers not always blue? As we know, many icebergs (and snow) are white.

The key here is "bubbles". The reason is that for each ice/air interface, part of the light gets reflected and only a fraction goes through. Therefore the greater the number of bubbles a piece of ice has, the less light will be able to proceed deeper into the ice. As such, when you view light from more bubbly ice, most of it will have traveled through less ice, and thus have had less distance to obtain the blue tint. I've made this figure to help understanding the idea: light in ice with bubbles diagram

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(Picture taken from peakglass.ca)

In the same way, glacier ice is blue, but that can only be appreciated if the piece of ice you are looking at is thick enough. We can see this effect in the following picture of an iceberg, where sections of different thicknesses displays a color gradient ranging from transparent to blue. ice colors

The remaining questions is: Why are glaciers then not always blue? As we know many icebergs (and deep snowssnow) are white.

However, there is a trick that can even make the blue color of seemingly-white snow noticeable. If you let a ray of light bounce on it many times, each time it will travel through a little bit of ice, getting a bit of blue tint each time, and after enough bounces it will look unquestionably blue. That's what you see when looking at the entrance of a snow cave or a crevasse in a glacier. The light that comes from deeper in the cave has bounced many more times around the walls and becomes bluer: enter image description here (Picture taken from outdoorlifenorway.com)

In the same way, glacier ice is blue, but that can only be appreciated if the piece of ice you are looking at is thick enough. We can see this effect in the following picture of an iceberg, where sections of different thicknesses displays a color gradient ranging from transparent to blue. ice colors

The remaining questions is: Why are glaciers then not always blue? As we know many icebergs (and deep snows) are white.

However, there is a trick that can even make the blue color of seemingly-white snow noticeable. If you let a ray of light bounce on it many times, each time it will travel through a little bit of ice, getting a bit of blue tint each time, and after enough bounces it will look unquestionably blue. That's what you see when looking at the entrance of a snow cave or a crevasse in a glacier. The light that comes from deeper in the cave has bounced many more times around the walls and becomes bluer: enter image description here

(Picture taken from peakglass.ca)

In the same way, glacier ice is blue, but that can only be appreciated if the piece of ice you are looking at is thick enough. We can see this effect in the following picture of an iceberg, where sections of different thicknesses displays a color gradient ranging from transparent to blue. ice colors

The remaining questions is: Why are glaciers then not always blue? As we know many icebergs (and snow) are white.

However, there is a trick that can even make the blue color of seemingly-white snow noticeable. If you let a ray of light bounce on it many times, each time it will travel through a little bit of ice, getting a bit of blue tint each time, and after enough bounces it will look unquestionably blue. That's what you see when looking at the entrance of a snow cave or a crevasse in a glacier. The light that comes from deeper in the cave has bounced many more times around the walls and becomes bluer: enter image description here (Picture taken from outdoorlifenorway.com)

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The short answer is: Because theBECAUSE THE ICE IS BLUE. 
Now we have to explain why it seemseems perfectly transparent on ice cubes and industrial ice blocks.

It havehas to do with the fact that most transparent materials are not perfectly transparent, and doinstead absorb (and/or scatter) part of the light that goes troughhits them. And when the transparency is better for one specific color (wavelength), the material will look of that color, much like a tintedhow stained glass that gives a tint to the white light that goes troughgoing through it.

Now the important fact is that this "tint" effect is stronger the thicker the material is. Let's take a standard glass as a example: When looking troughthrough the glass it seemseems perfectly transparent, because the thickness is too small to make its color noticeable. However, if you look at the edge of the glass, it looks green, something that showwhich shows that glass is indeed green, but that only became noticeable only when looking troughthrough a section thick enough.   

enter image description hereglass

In the same way, glacier ice is blue, but that can only be appreciated if the piece of ice you are looking at is thick enough. We can see this effect in the following picture of an iceberg, werewhere sections of different thicknesses shows colors gradingdisplays a color gradient ranging from transparent to blue. enter image description hereice colors

The remaining questions is: Why they are glaciers then not always blue? As we know many icebergs (and deep snows) are white. The same is trough for snow, that is ice after all.

The key here are the bubbleis bubbles. And theThe reason is that onfor each ice/air interface, part of the light gets reflected and only a fraction goes troughthrough. Therefore, the mostgreater the number of bubbles a piece of ice havehas, the less the light will be able to travel trough it before bouncing back out. Andproceed deeper into the less ice that. As such, when you view light from more bubbly ice, most of it will have gone troughtraveled through less ice, theand thus have had less distance to obtain the blue tint received. I've made this figure to help understanding the idea: enter image description herelight in ice with bubbles diagram

On the left, a piece of ice with very few bubbles allows a longer travel path troughthrough the ice, inducing a marked blue tint in the outgoing light. On the right, in contrast, if there are many bubbles the light will go bounce back right away with only a very subtle tint, or no tint at all.

Snow is the extreme of itthis, whichbecause it is mostly air (bubbles), and only some small pieces of ice, that's why it looks so white.

An interesting ramification of this, is that: those deep blue pieces of ice have started as snow. But as the snow piles up, the weight of the snow on top compacts it, squeezing the air out changing it from snow to firn until you end withfinally reach the density of being a block of ice with bubbles (which is officially the point it start to be considered ice, before it is snow or firnwith bubbles). In a big glacier, hundreds or thousands of meters of ice can exert such a pressure that the bubblesbubble spaces get compacted becoming smaller and smaller until they disappear and the air getsis dissolved ininto the ice itself. 
Therefore, this means that the more blue (and bubble-less and blue) a piece of ice is, it meansthe more it comeshas come from deeper inwithin the glacier,... meaning it also that comeshas traveled from further up in the glacier basin and it is, therefore, older. So, now you can identify deep, old ice just by its color.

To give a more familiar example of how adding bubbles can turn something transparent with a tint into something white, take the case of egg whitewhites, which is trasparentare transparent with a yellowyellowish tint. But as whyyou whip it, adding in bubbles, it begins to turn it into meringue thatwhich is perfectly white. enter image description heremaking meringue

However, there is a trick tothat can even make the blue color of the seemingly-white snow noticeable. And that is lettingIf you let a ray of light to bounce many times on it many times, each time it will travel through a little bit of ice, getting a bit of blue tint each time, and after enough timesbounces it will look unquestionably blue. That's what you see when looking at the entrance of a snow cave, or a crevasse in a glacier. The light that comes from deeper in the cave havehas bounced many more times inaround the walls becomingand becomes bluer: enter image description here

The short answer is: Because the ICE IS BLUE. Now we have to explain why it seem perfectly transparent on ice cubes and industrial ice blocks.

It have to do with the fact that most transparent materials are not perfectly transparent, and do absorb (and/or scatter) part of the light that goes trough them. And when the transparency is better for one specific color (wavelength), the material will look of that color, like a tinted glass that gives a tint to the white light that goes trough it.

Now the important fact is that "tint" effect is stronger the thicker the material is. Let's take a standard glass as a example: When looking trough the glass it seem perfectly transparent, because the thickness is too small to make its color noticeable. However, if you look at the edge of the glass, it looks green, something that show that glass is indeed green, but that became noticeable only when looking trough a section thick enough.  enter image description here

In the same way, glacier ice is blue, but that can only be appreciated if the piece of ice you are looking at is thick enough. We can see this effect in the following picture of an iceberg, were sections of different thicknesses shows colors grading from transparent to blue. enter image description here

The remaining questions is: Why they are not always blue? As we know many icebergs are white. The same is trough for snow, that is ice after all.

The key here are the bubble. And the reason is that on each ice/air interface, part of the light gets reflected and only a fraction goes trough. Therefore, the most bubbles a piece of ice have, the less the light will be able to travel trough it before bouncing back out. And the less ice that light have gone trough, the less the tint received. I've made this figure to help understanding the idea: enter image description here

On the left, a piece of ice with very few bubbles allows a longer travel path trough the ice, inducing a marked blue tint in the outgoing light. On the right, in contrast, if there are many bubbles the light will go back right away with a very subtle or no tint at all.

Snow is the extreme of it, which it is mostly air (bubbles), and some small pieces of ice, that's why it looks so white.

An interesting ramification of this, is that those deep blue pieces of ice have started as snow. But as snow piles up, the weight of the snow on top compacts it, squeezing the air out until you end with a block of ice with bubbles (which is officially the point it start to be considered ice, before it is snow or firn). In a big glacier, hundreds or thousands of meters of ice can exert such a pressure that the bubbles get compacted becoming smaller and smaller until they disappear and the air gets dissolved in the ice. Therefore, the more bubble-less and blue a piece of ice is, it means it comes from deeper in the glacier, meaning also that comes from further up in the glacier basin and it is, therefore, older. So, now you can identify deep, old ice just by its color.

To give a more familiar example of how adding bubbles can turn something transparent with a tint into something white, take the case of egg white, which is trasparent with a yellow tint. But as why whip it, adding bubbles, it to turn it into meringue that is perfectly white. enter image description here

However, there is a trick to make the color of the seemingly-white snow noticeable. And that is letting a ray of light to bounce many times on it, each time it will travel through a little bit of ice getting a bit of blue tint, and after enough times it will look unquestionably blue. That's what you see when looking at the entrance of a snow cave, or a crevasse in a glacier. The light that comes from deeper in the cave have bounced more times in the walls becoming bluer: enter image description here

The short answer is: BECAUSE THE ICE IS BLUE. 
Now we have to explain why it seems perfectly transparent on ice cubes and industrial ice blocks.

It has to do with the fact that most transparent materials are not perfectly transparent, and instead absorb (and/or scatter) part of the light that hits them. And when the transparency is better for one specific color (wavelength), the material will look that color, much like how stained glass gives a tint to the white light going through it.

Now the important fact is that this "tint" effect is stronger the thicker the material is. Let's take a standard glass as a example: When looking through the glass it seems perfectly transparent, because the thickness is too small to make its color noticeable. However, if you look at the edge of the glass, it looks green, which shows that glass is indeed green, but that only became noticeable when looking through a section thick enough. 

glass

In the same way, glacier ice is blue, but that can only be appreciated if the piece of ice you are looking at is thick enough. We can see this effect in the following picture of an iceberg, where sections of different thicknesses displays a color gradient ranging from transparent to blue. ice colors

The remaining questions is: Why are glaciers then not always blue? As we know many icebergs (and deep snows) are white.

The key here is bubbles. The reason is that for each ice/air interface, part of the light gets reflected and only a fraction goes through. Therefore the greater the number of bubbles a piece of ice has, the less light will be able to proceed deeper into the ice. As such, when you view light from more bubbly ice, most of it will have traveled through less ice, and thus have had less distance to obtain the blue tint. I've made this figure to help understanding the idea: light in ice with bubbles diagram

On the left, a piece of ice with very few bubbles allows a longer travel path through the ice, inducing a marked blue tint in the outgoing light. On the right, in contrast, if there are many bubbles the light will go bounce back right away with only a very subtle tint, or no tint at all.

Snow is the extreme of this, because it is mostly air (bubbles), and only some small pieces of ice, that's why it looks so white.

An interesting ramification of this: those deep blue pieces of ice started as snow. But as the snow piles up, the weight of the snow on top compacts it, squeezing air out changing it from snow to firn until you finally reach the density of being a block of ice (with bubbles). In a big glacier, hundreds or thousands of meters of ice can exert such a pressure that the bubble spaces get compacted smaller and smaller until they disappear and the air is dissolved into the ice itself. 
Therefore this means that the more blue (and bubble-less) a piece of ice is, the more it has come from deeper within the glacier... meaning it also has traveled from further up in the glacier basin and it is, therefore, older. So, now you can identify deep, old ice just by its color.

To give a more familiar example of how adding bubbles can turn something transparent with a tint into something white, take the case of egg whites, which are transparent with a yellowish tint. But as you whip it, adding in bubbles, it begins to turn into meringue which is perfectly white. making meringue

However, there is a trick that can even make the blue color of seemingly-white snow noticeable. If you let a ray of light bounce on it many times, each time it will travel through a little bit of ice, getting a bit of blue tint each time, and after enough bounces it will look unquestionably blue. That's what you see when looking at the entrance of a snow cave or a crevasse in a glacier. The light that comes from deeper in the cave has bounced many more times around the walls and becomes bluer: enter image description here

2 Corrected typos or spelling errors
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