There's only an option to completely delete your tumblr, but what you could do is set it private instead. with private feature, you'll need to enter a password to view the page. you don't have to give it to anyone if you don't want anyone seeing your tumblr. in case you don't know how: you can set your tumblr private by going to "settings" below "customize appearance" from your dashboard. scroll down to the bottom and tick the box where it says "password protect this blog"