Newbie question on checkpointing

I am running 8.0.5 on linux at home. It let it run during the day just to help me study for the OCP exam. I notice in the alert log a horrendous amount of checkpointing activity. Using the tail -f command on the alert log, it appears almost constant. Can anyone tell me why, especially when there is so little activity? A log excerpt and relevant parameters below. I was expecting to see a checkpoint every 30 minutes (1800 secs.) Thanks.

SVRMGR> show parameter checkpoint

NAME                                TYPE    VALUE
----------------------------------- ------- ------------------------------
db_block_checkpoint_batch           integer 8
log_checkpoint_interval             integer 10000
log_checkpoint_timeout              integer 1800
log_checkpoints_to_alert            boolean TRUE

Sun Jun 27 18:14:18 1999
Beginning interval checkpoint up to RBA [0x26c.b.10], SCN: 0x0000.0001af45 Completed checkpoint up to RBA [0x26c.b.10], SCN: 0x0000.0001af45 Beginning interval checkpoint up to RBA [0x26c.b.10], SCN: 0x0000.0001af46 Completed checkpoint up to RBA [0x26c.b.10], SCN: 0x0000.0001af46 Beginning interval checkpoint up to RBA [0x26c.b.10], SCN: 0x0000.0001af47 Completed checkpoint up to RBA [0x26c.b.10], SCN: 0x0000.0001af47 Beginning interval checkpoint up to RBA [0x26c.b.10], SCN: 0x0000.0001af48 Completed checkpoint up to RBA [0x26c.b.10], SCN: 0x0000.0001af48 Beginning interval checkpoint up to RBA [0x26c.b.10], SCN: 0x0000.0001af49 Completed checkpoint up to RBA [0x26c.b.10], SCN: 0x0000.0001af49

etc.
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