Barchan Block Puzzle

Out on the erg a barchan dune walks a few metres a year, and the caravan trays walk with it. Fill a row of glazed tiles and it falls back to sand; send that sand into the right gap and the whole tray settles in a rush.

A block puzzle on an 8x8 board: cleared blocks turn to sand and fall into the gaps below, setting off cascades. 30 Journey stages and races.

Three pieces wait beside the board. Drag one onto the board; a shadow shows where it will land and lights every row and column it will complete. A full row or column clears, and every cleared block that had an empty cell right under it crumbles into sand; a block resting on another block or on the floor has nowhere to pour, so its sand blows away, which is why a full column always clears clean. Sand always falls until it rests on a block, on other sand or on the floor, including sand that was lying on a line that just cleared; glazed blocks stay where you put them. Sand fills lines like any block, so a clear can finish the row below it and clear again: a cascade, and every step of it multiplies the points. Clearing on consecutive moves builds a streak that multiplies them again; the streak survives two moves without a clear and breaks on the third. When all three pieces are placed, three new ones arrive, and bigger shapes come more often as the run goes on. The run ends when none of the pieces fits anywhere. Journey mode has 30 stages in five places, each with its own starting board, a goal and a fixed number of pieces. On a keyboard, 1 to 3 picks a piece, the arrow keys move it and Enter or Space places it.