Bubbles from glacier ice turn up the noise in Alaska

2015-03-06 09:47
The deployment of a hydrophone in Icy Bay, Alaska. (Jeffrey Nystuen, AP)

The deployment of a hydrophone in Icy Bay, Alaska. (Jeffrey Nystuen, AP)

Multimedia   ·   User Galleries   ·   News in Pictures Send us your pictures  ·  Send us your stories

Anchorage - Glaciologist Erin Pettit began a research project to find out what humpback whales heard when a big piece of ice falls from a glacier and crashes into the ocean. But the sound generated by ice drifting in the water turned out to be just as interesting.

Acoustic research in Alaska's Icy Bay and other glacier ice-filled waters found that the fizz created by the release of pressurized air bubbles within glacier ice makes fjords the noisiest places in the ocean.

"The glacier fjord sound on a typical day for Icy Bay is louder than being in the water beneath a torrential downpour, which really surprised me," said Pettit, a researcher at the University of Alaska Fairbanks.

In a paper Pettit and fellow researchers speculate that one reason harbour seals flock to fjords with tidewater glaciers is because noisy icebergs provide acoustic camouflage, protecting seals from transient killer whales that hunt by sound.

In July 2009, the researchers deployed underwater microphones 70m deep in Icy Bay, a fjord near the top of the Alaska Panhandle just 6.5km from 5 500m Mount St Elias. They also sampled sound at nearby Yakutat Bay and at Andvord Bay in Antarctica.

Researcher Jeff Nystuen of the University of Washington's Applied Physics Laboratory, who had had used hydrophones to measure the underwater sound of rainfall, quickly realised the significance of the sound collected in the fjords, Pettit said.

"He was kind of blown away when I showed him the results of our data set," she said. "He's like, 'This is really, really loud.'"

Colleagues at the University of Texas at Austin conducted laboratory tests in acoustic tanks with Alaska glacier ice to find out how bubbles make noise.

They recorded air bubbles making a bloop, tick or pop sound as they separated from ice, a sound that lasts 10 milliseconds or less.

"The bubble rising through the water is relatively silent," Pettit said. "The bubble hitting the surface is also relatively silent."

The snow compressing to ice on a glacier creates bubbles of nearly the same size under the same pressure, Pettit said. That makes for consistent sound underwater.

"In terms of our hearing, the range of those notes is kind of that area that's on the upper half of the piano," she said. "It's centred about three-quarters of the way up to the high end of a piano."

In general, "It's kind of a combination of a babbling brook and a hissing sound," she said.

Read more on:    alaska  |  marine life  |  environment  |  research

Join the conversation!

24.com encourages commentary submitted via MyNews24. Contributions of 200 words or more will be considered for publication.

We reserve editorial discretion to decide what will be published.
Read our comments policy for guidelines on contributions.
NEXT ON NEWS24X

24.com publishes all comments posted on articles provided that they adhere to our Comments Policy. Should you wish to report a comment for editorial review, please do so by clicking the 'Report Comment' button to the right of each comment.

Comment on this story
0 comments
Comments have been closed for this article.

Inside News24

 
/News

Book flights

Compare, Book, Fly

Traffic Alerts
Traffic
There are new stories on the homepage. Click here to see them.
 
English
Afrikaans
isiZulu

Hello 

Create Profile

Creating your profile will enable you to submit photos and stories to get published on News24.


Please provide a username for your profile page:

This username must be unique, cannot be edited and will be used in the URL to your profile page across the entire 24.com network.

Settings

Location Settings

News24 allows you to edit the display of certain components based on a location. If you wish to personalise the page based on your preferences, please select a location for each component and click "Submit" in order for the changes to take affect.




Facebook Sign-In

Hi News addict,

Join the News24 Community to be involved in breaking the news.

Log in with Facebook to comment and personalise news, weather and listings.