Brilliant white ice fills the right half of this image. It is fast ice, and derives its name from the fact that it holds fast to the shore. This ice is thick enough to completely hide the underlying seawater, hence its brilliant white color.

Trapped within the fast ice, and stuck along the edge of it, are icebergs. Icebergs form by calving office shelves – thick slabs of ice attached to the coast. Ice shelves can range in thickness from tens to hundreds of meters, and the icebergs that calve off of them can tower over nearby sea ice. One iceberg, drenched with melt water, has toppled and shattered (image upper right). The water-saturated ice leaves a blue tinge.

The icebergs along the edge of the fast ice are likely grounded on the shallow sea floor, and their presence may help hold the fast ice in place.

Farther out to sea is pack ice that drifts with winds and currents. Much thinner than the fast ice, the translucent pack ice appears in shades of blue-gray.

The pack ice includes some newly formed sea ice. As seawater starts to freeze, it forms tiny crystals known as frazil (image center). Although the individual crystals are only millimeters across, enough of them assembled together are visible from space. Constantly moved by ocean currents, frazil often appears in delicate swirls. Frazil crystals can coalesce into thin sheets of ice known as nilas (image top). Sheets of nilas often slide over each other, eventually merging into thicker layers of ice.

A series of tropical storms and heavy monsoon rains combined to make 2011 the worst flood season on the lower Mekong River since 2000. Floods swept across Cambodia, impacting 17 of the country’s 24 provinces. As of October 18, at least 207 people have died in the floods and 34,000 families have been evacuated, said the Cambodian Red Cross.

These images compare seasonal flooding along the Mekong River and the Tonle Sap (Tônlé Sab) on October 18, 2011, and October 26, 2006. Taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Aqua and Terra satellites, the images include both infrared and visible light to increase the contrast between water and land. Water is black or dark blue, while the surrounding plant-covered land is green. Clouds are pale blue and white. Both the Tonle Sap and the Sen River flood Kompong Thom, one of the most severely impacted provinces in Cambodia. The Mekong River is also swollen in 2011 compared to 2006.

Devastating though the flood is, Southeast Asia revolves around the Mekong’s seasonal floods. Eighty to ninety percent of the river’s flow occurs during the flood season, which runs from June to November. This flush of water creates wetland habitats and draws nutrients from land into the river to feed a diverse fish population. The floods can damage crops, but they also lay down nutrient-rich soil that naturally fertilizes fields. The Mekong River Commission estimates that the annual flood causes 60 to 70 million dollars in damage, but brings 8 to 10 billion dollars into the economies of Southeast Asia.