Design a wordless educational illustration explaining how a river meander becomes an oxbow lake for middle-school students. Arrange four clearly separated stages from left to right: a gently curving channel, increasing outer-bank erosion and inner-bank deposition, floodwater cutting through the narrow neck, and sediment sealing the abandoned bend into an isolated oxbow lake. Keep the same overhead scale and water-flow direction in every stage. Use clean arrows, granular bank textures, and color changes to communicate current, erosion, deposition, cutoff, and sealing without labels. Compose the image in landscape 4:3 on a warm-white background with polished flat editorial shapes and subtle paper texture. Use blue-green water, sandy brown deposits, and soft green floodplain for easy comparison. Keep the geomorphology scientifically plausible. No readable text, letters, numbers, logos, watermark, buildings, people, or decorative icons.