Nice game, although perhaps a bit too hard, the best I did was reaching the point where yellow part of the volcano is a circle with a radius of about 4 or 5 pixels. Speaking of which, it would be nice to add a distance counter/indicator, i.e. something to track "score". And, speaking of addition, it would also be nice to have easy/medium/hard option (which should be trivial to implement e.g. by starting out with different number of hearts and/or different debris density (i.e. spawn rate)).
I acknowledge that the game is currently unfinished, so I hope some of these suggestions might be helpful for further development. :)
Overall, it is fun and challenging to play. Well done! :)