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Why Some Mountain Lakes Glow Turquoise

6th grade nonfiction passage about glacier lakes and their color: 224 words, six questions, an answer key and vocabulary.

6th grade nonfiction glacier lakes and their color 224 words

Why Some Mountain Lakes Glow Turquoise

Photographs of some mountain lakes look as if someone has colored the water with paint. The lake is a bright, milky turquoise, a shade somewhere between blue and green. Yet nothing has been added to it. The color comes from rock.

High in the mountains, a glacier is a huge, slow river of ice. As it creeps downhill, it drags rocks along its bed and grinds them against the ground beneath. The grinding crushes the stone into a fine powder, called rock flour, that is as soft as flour from a kitchen.

When the glacier's ice melts, the meltwater carries the rock flour into streams, and the streams run into a lake. The grains are so tiny that they stay floating in the water for a long time instead of sinking quickly. They make the lake look cloudy, much like a drop of milk in a glass.

Sunlight is a mixture of many colors. When it strikes the floating grains, they scatter it. The grains reflect blue and green light back toward your eyes more than the other colors, and that is why the lake looks turquoise.

The color changes with the seasons. In summer, more ice melts and more rock flour pours in, so the lake is usually its brightest. In winter, when the melting slows, the water often turns clearer and darker.

Questions

  1. What is rock flour? in the text

  2. How does rock flour get into a lake? in the text

  3. Why do the grains stay floating instead of sinking quickly? in the text

  4. Which colors of light do the grains reflect most? in the text

  5. Why is the lake usually brightest in summer? think about it

  6. What clue shows that nothing was added to the water to color it? think about it

Words to know

glacier
a huge, slow-moving mass of ice on land
turquoise
a bright color between blue and green
meltwater
water that comes from melting ice or snow
scatter
to send in many different directions
powder
a very fine dust of tiny grains
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One passage, three levels

The same topic and facts written three ways, so a mixed class can read and talk about one text. Each group’s sheet shows only a shape; the key says which is which.

● Easier · 209 words · Flesch-Kincaid grade 3.3

Pictures of some mountain lakes look as if someone painted the water. The lake is a bright, milky turquoise, a color between blue and green. But nothing was added to it. The color comes from rock.

High in the mountains, a glacier is a huge, slow river of ice. As it creeps downhill, it drags rocks along the ground. The rocks grind against the ground under the ice. The grinding crushes stone into a fine powder, called rock flour. It is as soft as flour from a kitchen.

When the ice melts, the meltwater carries the rock flour into streams. The streams run into a lake. The grains are so tiny that they float in the water for a long time. They make the lake look cloudy, like a drop of milk in a glass.

Sunlight is a mix of many colors. When it hits the floating grains, they scatter it. The grains send blue and green light back to your eyes more than the other colors. That is why the lake looks turquoise.

The color changes with the seasons. In summer, more ice melts, and more rock flour pours in. The lake is usually brightest. In winter, the melting slows, and the water often turns clearer and darker.

▲ This passage · 224 words · Flesch-Kincaid grade 5.2

Photographs of some mountain lakes look as if someone has colored the water with paint. The lake is a bright, milky turquoise, a shade somewhere between blue and green. Yet nothing has been added to it. The color comes from rock.

High in the mountains, a glacier is a huge, slow river of ice. As it creeps downhill, it drags rocks along its bed and grinds them against the ground beneath. The grinding crushes the stone into a fine powder, called rock flour, that is as soft as flour from a kitchen.

When the glacier's ice melts, the meltwater carries the rock flour into streams, and the streams run into a lake. The grains are so tiny that they stay floating in the water for a long time instead of sinking quickly. They make the lake look cloudy, much like a drop of milk in a glass.

Sunlight is a mixture of many colors. When it strikes the floating grains, they scatter it. The grains reflect blue and green light back toward your eyes more than the other colors, and that is why the lake looks turquoise.

The color changes with the seasons. In summer, more ice melts and more rock flour pours in, so the lake is usually its brightest. In winter, when the melting slows, the water often turns clearer and darker.

■ Harder · 243 words · Flesch-Kincaid grade 6.9

Photographs of certain mountain lakes look as though someone has tinted the water with paint. The lake glows a brilliant, milky turquoise, a shade somewhere between blue and green. Yet nothing has been added to it whatsoever. The color comes entirely from rock.

High in the mountains, a glacier is a vast, slow river of ice. As it creeps downhill, it drags boulders and stones along its bed and grinds them against the ground beneath. This relentless grinding crushes the stone into an extremely fine powder, called rock flour, that is nearly as soft as the flour in a kitchen cupboard.

When the glacier's ice melts, the meltwater sweeps the rock flour into streams, and those streams empty into a lake. The grains are so minuscule that they remain suspended in the water for a long time rather than sinking quickly. They give the lake a cloudy appearance, much like a drop of milk stirred into a glass of water.

Sunlight is a mixture of many colors. When it strikes the suspended grains, they scatter it in every direction. The grains reflect blue and green light back toward your eyes more strongly than the other colors, and that is the reason the lake appears turquoise.

The color shifts with the seasons. In summer, more ice melts and more rock flour pours in, so the lake is generally at its brightest. In winter, when the melting slows, the water often becomes clearer and darker.

Download as one PDF

How to use it

  1. Press Read it big (or B) to put the text on the projector, or Full screen (F) to fill the whole screen.
  2. Ask the questions one at a time and use Show answer when the class has decided. A shows or hides every answer.
  3. Print student copy for the class, or Print with answers for yourself.

Ideas for class

  • Before reading, put glacier, turquoise, meltwater, scatter and powder on the board with their meanings from the Words to know section and have students predict what the text will be about.
  • Read it aloud once while students follow along, then have them reread it alone or with a partner. At a calm 100 words a minute it takes about 2 minutes to read aloud.
  • Use the Read it big button (or B) to put the text on the projector, and Show answer on one question at a time so the class commits to an answer first.
  • Question 5 asks the reader to infer. Ask students to point to the words in the passage that led them to their answer.
  • Ask students to write one question the passage did not answer, then look for the answer in a book or on a classroom screen.
  • Print the student copy for independent work and keep the answer-key copy for yourself.

Related

Questions

What reading level is "Why Some Mountain Lakes Glow Turquoise"?

It was written for 6th grade. It has 224 words and works out to a Flesch-Kincaid grade level of about 5.2. That is a formula's estimate from sentence length and syllables, and it is not a Lexile or a guided reading level, so check it against your students.

What do the questions ask?

There are six. 4 ask for something the text says directly and 2 ask the reader to work something out from clues. Each has an answer in the key, and the answers are written as a teacher would accept them, not as the only possible wording.

How long does it take to read?

About 2 minutes read aloud at 100 words a minute. For a one-minute fluency check, paste it into the fluency timer and use the word count.

Can I print it?

Yes. Print student copy gives the passage, the questions with lines to write on, and the word meanings. Print with answers gives the same page with the answers filled in. Both are made in your browser.

Is this passage from a published book?

No. It was written for Peabody Teach, so there is no book to buy and no login to read it.

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