We’ve done our own processing on a NASA / MODIS satellite image showing a large smoke plume coming from the port city of Sendai. The image was taken from the Aqua satellite at 12:10 pm local time on March 12. The magnitude 8.9 quake struck at 2:46 pm local time on March 11, and tsunami waves crashed ashore along the northeastern coast of Japan shortly after.
The dark brown smoke plume stretches to the southeast, reaching at least 115 kilometers (73 miles) over the ocean.
Notice the bright turquoise patterns in the water; this is turbidity, quite possibly sand stirred up from the seafloor by the scouring action of the massive waves, and debris and sediment from flooded coastal areas dragged out to sea as the waves receded. Clouds and snow are bright white in this image, processed to enhance the smoke and turbidity: