IPY/NSTA Web Seminar:

The Fragile Ice

LIVE INTERACTIVE LEARNING @ YOUR DESKTOP

Thursday, May 3, 2007

7:00 p.m. to 8:00 p.m. Eastern time

Snow: a Winter’s Tale- or -

Evidence of the Past from Snow on the Ground

Mary Albert, Ph.D.Army Cold Regions Research & Engineering Laboratory

andDartmouth Thayer School of Engineering

International Polar Year

Take the pulse of the poles. Biggest effort in 50 years

• Arctic observing network• Life in extreme environments• Polar ice sheets• Education and outreach• www.us-ipy.gov (U.S.)• www.ipy.org (International)

A “beehive” of activity

Snow characteristicsAntarctica from space

BPRC Ohio State

M. Albert for NSTA 2007

Ice sheets hold evidence of changing climate. Snow in your yard has evidence of changing weather.

• What causes different layers in snow on the ground?• What causes changes in snow crystals once they are

on the ground?• How can snow on the ground give evidence of past

weather?

M. Albert for NSTA 2007

Falling Snow

M. Albert for NSTA 2007

No two snow crystals falling from the sky are alike. But are they all dendritic, like the Christmas tree ornaments?

Yes No

Falling Snow

Libbrecth & Rasmussen, 2006

The shape of falling snow crystals depends on temperature and humidity in the atmosphere.

M. Albert for NSTA 2007

Snow layer formation

M. Albert for NSTA 2007

Layers of snow on the ground are from different depositional events. They provide evidence about different snow (or rain!) storms.

Snow on the ground

Colbeck et al, 1990

Snow crystal shape changes in time due to metamorphism.

Crystals become more faceted when there is a strong temperature gradient across the layer.

M. Albert for NSTA 2007

Which layer in this snow pack has faceted crystals?

Snow on the ground

M. Albert for NSTA 2007

Snow on the ground

Colbeck et al, 1990

Snow crystals get more rounded as they experience warmer conditions.

M. Albert for NSTA 2007

A temperature gradient is a difference in temperature between two points a certain distance apart.

M. Albert for NSTA 2007

At temperatures below freezing, why would a temperature gradient cause metamorphism?

Snow crystals contract as it gets colder

Snow crystals expand as it gets colder

Water vapor moves and

condenses on crystals

Surface chemistry

changes the grain shape

This difference in vapor pressure causes the vapor to diffuse from the region of higher vapor pressure to the region of lower vapor pressure.

Warmer air can hold more water vapor than colder air.

So warmer air has higher vapor pressure than colder air.

warmercolder

M. Albert for NSTA 2007

warmercolder

M. Albert for NSTA 2007

Summary

Do snow crystals change when there is no change in temperature?

Yes No

M. Albert for NSTA 2007

M. Albert for NSTA 2007

M. Albert for NSTA 2007

M. Albert for NSTA 2007

How do snow layers behave throughout the winter and into spring?

M. Albert for NSTA 2007

Sprayed-on dye helps to show snow layering

Before After

M. Albert for NSTA 2007

(m)

M. Albert for NSTA 2007

Air

tem

per

atu

re

(C)

Some of the layers are labeled.

Which layer(s) will change first due to changing weather?

Layer 1 Layer 7 All of them

M. Albert for NSTA 2007

When the snow melts, do all layers melt at the same time ?

Surface snow changes the most in response to changing weather.

M. Albert for NSTA 2007

The top layer shows the most change due to changing weather.

M. Albert for NSTA 2007

During much of the melt season, surface melt percolates through melt channels in the snow.

M. Albert for NSTA 2007

Subsurface layers remain intact through much of the winter, providing evidence about the storm that created them.

M. Albert for NSTA 2007

Evidence of the Past in Snow• Snow on the ground gives evidence of past weather.

• The snow near the top of the snow pack changes first, in response to changes in the weather.

• Snow crystal properties give evidence of warming or cooling weather in the recent past.

• The International Classification for Snow on the Ground (Colbeck et al 1990) is a guide you can use for metamorphism clues: http://www.crrel.usace.army.mil/techpub/CRREL_Reports/reports/Seasonal_Snow.pdf

• Understanding how nature works helps us to use clues to learn about the past.

• You can be a weather detective with your class by making notes of daily weather & snowfall over time. Then dig a snow pit and look at the snow layers to see how the evidence of weather found in the snow pack correlates with your notes of the observed weather.

M. Albert for NSTA 2007

NASA

M. Albert for NSTA 2007

Ice sheets hold evidence of past climate.The surface conditions reflect current climate, and layers within in

the ice contain evidence of the past. Evidence of climate thousands to hundreds of thousands of years ago hides deep in the ice sheet, waiting for ice coring science to unlock the clues.

Follow IPY science on these web sites:

www.ipy.govwww.ipy.org

Follow our scientific traverse across Antarctica at:

http://traverse.npolar.no

See teachers in the field at:www.polartrec.com

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