Ships in the south Pacific Ocean have been alerted that groups of icebergs believed to have split off Antarctic ice shelves are drifting north toward New Zealand, officials said Tuesday.
The alert comes three years after cold weather and favorable ocean currents saw dozens of icebergs float close to New Zealand's southern shores for the first time in 75 years.
Rodney Russ, expedition leader on the tourist ship Spirit of Enderby, spotted one iceberg Monday, 57 miles (92 kilometers) northeast of Macquarie Island and heading north _ about 500 miles (800 kilometers) south of New Zealand.
The iceberg was up to 500 feet (150 meters) long and 80-90 feet (25-30 meters) high, he said. The vessel located another large iceberg on its radar and chunks of ice floating nearby, he added.
Four icebergs were spotted last week off Auckland Islands, 250 miles (400 kilometers) south of New Zealand and heading slowly toward the country.
Australian scientists reported another mass of 20 icebergs drifting north past Macquarie Island two weeks ago. Glaciologist Neal Young said satellite images showed the group of icebergs, spread over a sea area of 600 by 440 miles (1,000 kilometers by 700 kilometers), moving on ocean currents away from Antarctica.
New Zealand maritime officials have issued navigation warnings for that area.
"It's an alert to shipping to be aware these potential hazards are around and to be on the lookout for them," Maritime New Zealand spokeswoman Sophie Hazelhurst said.
Large numbers of icebergs last floated close to New Zealand in 2006, when some were visible from the coastline in the first such sighting since 1931.
It is rare for whole icebergs to drift so far north before melting, but a cold snap around southern New Zealand and favorable ocean currents have again combined to push the towering visitors to the region intact.
Icebergs are formed as the ice shelf develops. Snow falls on the ice sheet and forms more ice, which flows to the edges of the floating ice shelves. Eventually, pieces around the edge break off.