It's hard to tell from this photo how tall these bizarre formations are - can you guess? Are they towering pinnacles hundred of feet high, or are they so tiny they could be crushed underfoot? Actually, they are in-between, standing 3 to 4 feet tall. These bizarre formations, known as "sand tufas," are found near the shores of California's Mono Lake.
How are sand tufas formed? Similar in appearance to the more famous calcium carbonate tufa towers along Mono Lake's shoreline, these sand tufas formed quite differently. Beneath the surface of the ancient lake, calcium-rich groundwater rose up through brine-saturated sand layers, forming cemented pillars of sand. Later, the lake waters receded, leaving this area high and dry some distance back from the water's edge. Then wind eroded away the sand layers, exposing fluted sand tufas which resemble the columns of some ancient ruined city. Only somewhat protected by their top harder layer, these delicate formations are being continually weathered completely away, and new ones are exposed.
This photograph appeared on NASA/USRA's Earth Science Picture of the Day site on November 24, 2004.