Tourists watch chinstrap penguins atop an iceberg in Antarctica in this undated photo.

This cruise season during the Southern Hemisphere summer—roughly November through February—more than 30,000 people are expected to visit the southernmost continent on 50 different ships, according to the International Association of Antarctic Tour Operators, a trade group.

When the ship crews are counted the total number exceeds 50,000.

The tourism boom increases the chances of accidents in the icy waters such as the Explorer sinking, says Jon Bowermaster, a National Geographic Society Expeditions Council grantee who was onboard the first vessel to arrive on the accident scene.

(National Geographic News is owned by the National Geographic Society.)

• More Photos in the News
• Today's Top 15 Most Popular Stories
• Free Email Newsletter: "Focus on Photography"